ltc1992 family - low power, fully differential input ... · the ltc ®1992 product family consists...

LTC1992 Family

11992fb

TYPICAL APPLICATION

FEATURES DESCRIPTION

Low Power, Fully Differential Input/Output

Amplifier/Driver Family

The LTC®1992 product family consists of five fully differen-tial, low power amplifiers. The LTC1992 is an unconstrained fully differential amplifier. The LTC1992-1, LTC1992-2, LTC1992-5 and LTC1992-10 are fixed gain blocks (with gains of 1, 2, 5 and 10 respectively) featuring precision on-chip resistors for accurate and ultrastable gain. All of the LTC1992 parts have a separate internal common mode feedback path for outstanding output phase balancing and reduced second order harmonics. The VOCM pin sets the output common mode level independent of the input common mode level. This feature makes level shifting of signals easy.

The amplifiers’ differential inputs operate with signals ranging from rail-to-rail with a common mode level from the negative supply up to 1.3V from the positive supply. The differential input DC offset is typically 250μV. The rail-to-rail outputs sink and source 10mA. The LTC1992 is stable for all capacitive loads up to 10,000pF.

The LTC1992 can be used in single supply applications with supply voltages as low as 2.7V. It can also be used with dual supplies up to ±5V. The LTC1992 is available in an 8-pin MSOP package.

Single-Supply, Single-Ended to Differential Conversion

APPLICATIONS

n Available with Adjustable Gain or Fixed Gain of 1, 2, 5 or 10

n ±0.3% (Max) Gain Error from –40°C to 85°C n 3.5ppm/°C Gain Temperature Coefficientn 5ppm Gain Long Term Stabilityn Fully Differential Input and Outputn CLOAD Stable up to 10,000pFn Adjustable Output Common Mode Voltagen Rail-to-Rail Output Swingn Low Supply Current: 1mA (Max)n High Output Current: 10mA (Min)n Specified on a Single 2.7V to ±5V Supplyn DC Offset Voltage <2.5mV (Max)n Available in 8-Lead MSOP Package

n Differential Driver/Receivern Differential Amplificationn Single-Ended to Differential Conversionn Level Shiftingn Trimmed Phase Response for Multichannel Systems

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.

–

–+

+

5V

5V

LTC1992

3

6

VOCM

VMID 0V

2.5V

0V

VIN

0.01μF

1992 TA01a

4

5

2

7

8

110k

10k

10k

10k

5V

0V

5V

–5V

2.5V

INPUT SIGNALFROM A

±5V SYSTEM

OUTPUT SIGNALFROM A

SINGLE-SUPPLY SYSTEM

VIN(5V/DIV)

+OUT

–OUT

(2V/DIV)

5V

0V

–5V

5V

0V

1992 TA01b

LTC1992 Family

21992fb

ABSOLUTE MAXIMUM RATINGS

Total Supply Voltage (+VS to –VS) .............................12VMaximum Voltage on any Pin ................ (–VS – 0.3V) ≤ VPIN ≤ (+VS + 0.3V)Output Short-Circuit Duration (Note 3) ............ IndefiniteOperating Temperature Range (Note 5)

LTC1992CMS8/LTC1992-XCMS8/ LTC1992IMS8/LTC1992-XIMS8 ...........–40°C to 85°C LTC1992HMS8/LTC1992-XHMS8 ...... –40°C to 125°C

(Note 1)

PIN CONFIGURATION

ORDER INFORMATIONLEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION SPECIFIED TEMPERATURE RANGE

LTC1992CMS8#PBF LTC1992CMS8#TRPBF LTYU 8-Lead Plastic MSOP 0°C to 70°C

LTC1992IMS8#PBF LTC1992IMS8#TRPBF LTYU 8-Lead Plastic MSOP –40°C to 85°C

LTC1992HMS8#PBF LTC1992HMS8#TRPBF LTYU 8-Lead Plastic MSOP –40°C to 125°C

LTC1992-1CMS8#PBF LTC1992-1CMS8#TRPBF LTACJ 8-Lead Plastic MSOP 0°C to 70°C

LTC1992-1IMS8#PBF LTC1992-1IMS8#TRPBF LTACJ 8-Lead Plastic MSOP –40°C to 85°C

LTC1992-1HMS8#PBF LTC1992-1HMS8#TRPBF LTACJ 8-Lead Plastic MSOP –40°C to 125°C

LTC1992-2CMS8#PBF LTC1992-2CMS8#TRPBF LTYV 8-Lead Plastic MSOP 0°C to 70°C

LTC1992-2IMS8#PBF LTC1992-2IMS8#TRPBF LTYV 8-Lead Plastic MSOP –40°C to 85°C

LTC1992-2HMS8#PBF LTC1992-2HMS8#TRPBF LTYV 8-Lead Plastic MSOP –40°C to 125°C

LTC1992-5CMS8#PBF LTC1992-5CMS8#TRPBF LTACK 8-Lead Plastic MSOP 0°C to 70°C

LTC1992-5IMS8#PBF LTC1992-5IMS8#TRPBF LTACK 8-Lead Plastic MSOP –40°C to 85°C

LTC1992-5HMS8#PBF LTC1992-5HMS8#TRPBF LTACK 8-Lead Plastic MSOP –40°C to 125°C

LTC1992-10CMS8#PBF LTC1992-10CMS8#TRPBF LTACL 8-Lead Plastic MSOP 0°C to 70°C

LTC1992-10IMS8#PBF LTC1992-10IMS8#TRPBF LTACL 8-Lead Plastic MSOP –40°C to 85°C

LTC1992-10HMS8#PBF LTC1992-10HMS8#TRPBF LTACL 8-Lead Plastic MSOP –40°C to 125°C

Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.

Consult LTC Marketing for information on non-standard lead based finish parts.

For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/

Specified Temperature Range (Note 6) LTC1992CMS8/LTC1992-XCMS8 ............. 0°C to 70°C LTC1992IMS8/LTC1992-XIMS8 ...........–40°C to 85°C LTC1992HMS8/LTC1992-XHMS8 ...... –40°C to 125°CStorage Temperature Range ................. –65°C to 150°CLead Temperature (Soldering, 10 sec) ................... 300°C

LTC1992 LTC1992-X

1

2

3

4

–IN

VOCM+VS

+OUT

8

7

6

5

+IN

VMID–VS–OUT

TOP VIEW

MS8 PACKAGE8-LEAD PLASTIC MSOP

++

––

TJMAX = 150°C, θJA = 250°C/W

1

2

3

4

–IN

VOCM+VS

+OUT

8

7

6

5

+IN

VMID–VS–OUT

TOP VIEW

MS8 PACKAGE8-LEAD PLASTIC MSOP

++

––

TJMAX = 150°C, θJA = 250°C/W

LTC1992 Family

31992fb

ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. +VS = 5V, –VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined as (+VOUT + –VOUT)/2. VINCM is defined as (+VIN + –VIN)/2. VINDIFF is defined as (+VIN – –VIN). VOUTDIFF is defined as (+VOUT – –VOUT). Specifications applicable to all parts in the LTC1992 family.

SYMBOL PARAMETER CONDITIONS

ALL C AND I GRADE ALL H GRADE

UNITSMIN TYP MAX MIN TYP MAX

VS Supply Voltage Range l 2.7 11 2.7 11 V

IS Supply Current VS = 2.7V to 5V

VS = ±5V

l

l

0.650.750.70.8

1.01.21.21.5

0.650.80.70.9

1.01.51.21.8

mAmAmAmA

VOSDIFF Differential Offset Voltage(Input Referred) (Note 7)

VS = 2.7VVS = 5VVS = ±5V

l

l

l

±0.25±0.25±0.25

±2.5±2.5±2.5

±0.25±0.25±0.25

±4±4±4

mVmVmV

ΔVOSDIFF/ΔT Differential Offset Voltage Drift(Input Referred) (Note 7)

VS = 2.7VVS = 5VVS = ±5V

l

l

l

101010

101010

μV/°CμV/°CμV/°C

PSRR Power Supply Rejection Ratio(Input Referred) (Note 7)

VS = 2.7V to ±5V l 75 80 72 80 dB

GCM Common Mode Gain(VOUTCM/VOCM)Common Mode Gain ErrorOutput Balance (ΔVOUTCM/(ΔVOUTDIFF) VOUTDIFF = –2V to +2V

l

l

l

1±0.1–85

±0.3–60

1±0.1–85

±0.35–60

%dB

VOSCM Common Mode Offset Voltage (VOUTCM – VOCM)

VS = 2.7VVS = 5VVS = ±5V

l

l

l

±0.5±1±2

±12±15±18

±0.5±1±2

±15±17±20

mVmVmV

ΔVOSCM/ΔT Common Mode Offset Voltage Drift VS = 2.7VVS = 5VVS = ±5V

l

l

l

101010

101010

μV/°CμV/°CμV/°C

VOUTCMR Output Signal Common Mode Range(Voltage Range for the VOCM Pin)

l (–VS) + 0.5V (+VS) – 1.3V (–VS) + 0.5V (+VS) – 1.3V V

RINVOCM Input Resistance, VOCM Pin l 500 500 MΩ

IBVOCM Input Bias Current, VOCM Pin VS = 2.7V to ±5V l ±2 ±2 pA

VMID Voltage at the VMID Pin l 2.44 2.50 2.56 2.43 2.50 2.57 V

VOUT Output Voltage, High (Note 2)

VS = 2.7V, Load = 10kVS = 2.7V, Load = 5mAVS = 2.7V, Load = 10mA

l

l

l

2.602.502.29

2.692.612.52

2.602.502.29

2.692.612.52

VVV

Output Voltage, Low (Note 2)

VS = 2.7V, Load = 10kVS = 2.7V, Load = 5mAVS = 2.7V, Load = 10mA

l

l

l

0.020.100.20

0.100.250.35

0.020.100.20

0.100.250.41

VVV

Output Voltage, High (Note 2)

VS = 5V, Load = 10kVS = 5V, Load = 5mAVS = 5V, Load = 10mA

l

l

l

4.904.854.75

4.994.904.81

4.904.804.70

4.994.904.81

VVV


VS = 5V, Load = 10kVS = 5V, Load = 5mAVS = 5V, Load = 10mA

l

l

l

0.020.100.20

0.100.250.35

0.020.100.20

0.100.300.42

VVV

Output Voltage, High (Note 2)

VS = ±5V, Load = 10kVS = ±5V, Load = 5mAVS = ±5V, Load = 10mA

l

l

l

4.904.854.65

4.994.894.80

4.854.804.60

4.994.894.80

VVV


VS = ±5V, Load = 10kVS = ±5V, Load = 5mAVS = ±5V, Load = 10mA

l

l

l

–4.99–4.90–4.80

–4.90–4.75–4.65

–4.98–4.90–4.80

–4.85–4.75–4.55

VVV

LTC1992 Family

41992fb

ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. +VS = 5V, –VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined as (+VOUT + –VOUT)/2. VINCM is defined as (+VIN + –VIN)/2. VINDIFF is defined as (+VIN – –VIN). VOUTDIFF is defined as (+VOUT – –VOUT). Specifications applicable to all parts in the LTC1992 family.


ALL C AND I GRADE ALL H GRADE


ISC Output Short-Circuit Current Sourcing (Notes 2,3)

VS = 2.7V, VOUT =1.35VVS = 5V, VOUT = 2.5VVS = ±5V, VOUT = 0V

l

l

l

202020

303030

202020

303030

mAmAmA

Output Short-Circuit Current Sinking (Notes 2,3)

VS = 2.7V, VOUT =1.35VVS = 5V, VOUT = 2.5VVS = ±5V, VOUT = 0V

l

l

l

131313

303030

131313

303030

mAmAmA

AVOL Large-Signal Voltage Gain l 80 80 dB

The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. +VS = 5V, –VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined as (+VOUT + –VOUT)/2. VINCM is defined as (+VIN + –VIN)/2. VINDIFF is defined as (+VIN – –VIN). VOUTDIFF is defined as (+VOUT – –VOUT). Specifications applicable to the LTC1992 only.


LTC1992CMS8LTC1992ISM8 LTC1992HMS8


IB Input Bias Current VS = 2.7V to ±5V l 2 250 2 400 pA

IOS Input Offset Current VS = 2.7V to ±5V l 0.1 100 0.1 150 pA

RIN Input Resistance l 500 500 MΩ

CIN Input Capacitance l 3 3 pF

en Input Referred Noise Voltage Density f = 1kHz 35 35 nV/√Hz

in Input Noise Current Density f = 1kHz 1 1 fA/√Hz

VINCMR Input Signal Common Mode Range l (–VS) – 0.1V (+VS) – 1.3V (–VS) – 0.1V (+VS) – 1.3V V

CMRR Common Mode Rejection Ratio(Input Referred)

VINCM = –0.1V to 3.7V l 69 90 69 90 dB

SR Slew Rate (Note 4) l 0.5 1.5 0.5 1.5 V/μs

GBW Gain-Bandwidth Product(fTEST = 100kHz)

TA = 25°CLTC1992CMS8LTC1992IMS8/LTC1992HMS8

l

l

3.02.51.9

3.23.0

3.54.04.0

3.0

1.9

3.2 3.5

4.0

MHzMHzMHz

LTC1992 Family

51992fb

ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. +VS = 5V, –VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined as (+VOUT + –VOUT)/2. VINCM is defined as (+VIN + –VIN)/2. VINDIFF is defined as (+VIN – –VIN). VOUTDIFF is defined as (+VOUT – –VOUT). Typical values are at TA = 25°C. Specifications apply to the LTC1992-1 only.


LTC1992-1CMS8LTC1992-1ISM8 LTC1992-1HMS8


GDIFF Differential GainDifferential Gain ErrorDifferential Gain NonlinearityDifferential Gain Temperature Coefficient

l

l

1±0.1503.5

±0.31

±0.1503.5

±0.35V/V

%ppm

ppm/°C

en Input Referred Noise Voltage Density (Note 7) f = 1kHz 45 45 nV/√Hz

RIN Input Resistance, Single-Ended +IN, –IN Pins l 22.5 30 37.5 22 30 38 kΩ

VINCMR Input Signal Common Mode Range VS = 5V –0.1V to 4.9V –0.1V to 4.9V V

CMRR Common Mode Rejection Ratio (Amplifier Input Referred) (Note 7)

VINCM = –0.1V to 3.7V l 55 60 55 60 dB

SR Slew Rate (Note 4) l 0.5 1.5 0.5 1.5 V/μs

GBW Gain-Bandwidth Product fTEST = 180kHz 3 3 MHz

The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. +VS = 5V, –VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined as (+VOUT + –VOUT)/2. VINCM is defined as (+VIN + –VIN)/2. VINDIFF is defined as (+VIN – –VIN). VOUTDIFF is defined as (+VOUT – –VOUT). Typical values are at TA = 25°C. Specifications apply to the LTC1992-2 only.





l

l

2±0.1503.5

±0.32

±0.1503.5

±0.35V/V

%ppm

ppm/°C





VINCM = –0.1V to 3.7V l 55 60 55 60 dB

SR Slew Rate (Note 4) l 0.7 2 0.7 2 V/μs


LTC1992 Family

61992fb

ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. +VS = 5V, –VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined as (+VOUT + –VOUT)/2. VINCM is defined as (+VIN + –VIN)/2. VINDIFF is defined as (+VIN – –VIN). VOUTDIFF is defined as (+VOUT – –VOUT). Typical values are at TA = 25°C. Specifications apply to the LTC1992-5 only.





l

l

5±0.1503.5

±0.35

±0.1503.5

±0.35V/V

%ppm

ppm/°C





VINCM = –0.1V to 3.7V l 55 60 55 60 dB



The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. +VS = 5V, –VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined as (+VOUT + –VOUT)/2. VINCM is defined as (+VIN + –VIN)/2. VINDIFF is defined as (+VIN – –VIN). VOUTDIFF is defined as (+VOUT – –VOUT). Typical values are at TA = 25°C. Specifications apply to the LTC1992-10 only.





l

l

10±0.1503.5

±0.310

±0.1503.5

±0.35V/V

%ppm

ppm/°C





VINCM = –0.1V to 3.7V l 55 60 55 60 dB



Note 1: Stresses beyond those listed under Absolute Maximum Ratings

may cause permanent damage to the device. Exposure to any Absolute

Maximum Rating condition for extended periods may affect device

reliability and lifetime.

Note 2: Output load is connected to the midpoint of the +VS and –VS

potentials. Measurement is taken single-ended, one output loaded at a

time.

Note 3: A heat sink may be required to keep the junction temperature

below the absolute maximum when the output is shorted indefinitely.

Note 4: Differential output slew rate. Slew rate is measured single ended

and doubled to get the listed numbers.

Note 5: The LTC1992C/LTC1992-XC/LTC1992I/LTC1992-XI are guaranteed

functional over an operating temperature of –40°C to 85°C. The

LTC1992H/LTC1992-XH are guaranteed functional over the extended

operating temperature of –40°C to 125°C.

Note 6: The LTC1992C/LTC1992-XC are guaranteed to meet the specified

performance limits over the 0°C to 70°C temperature range and are

designed, characterized and expected to meet the specified performance

limits over the –40°C to 85°C temperature range but are not tested or QA

sampled at these temperatures. The LTC1992I/LTC1992-XI are guaranteed

to meet the specified performance limits over the –40°C to 85°C

temperature range. The LTC1992H/LTC1992-XH are guaranteed to meet the

specified performance limits over the –40°C to 125°C temperature range.

Note 7: Differential offset voltage, differential offset voltage drift, CMRR,

noise voltage density and PSRR are referred to the internal amplifier’s

input to allow for direct comparison of gain blocks with discrete amplifiers.

LTC1992 Family

71992fb

TYPICAL PERFORMANCE CHARACTERISTICS

Common Mode Offset Voltagevs VOCM Voltage



Output Voltage Swing vs Output Load, VS = 2.7V

Output Voltage Swing vs Output Load, VS = 5V

Supply Current vs Supply VoltageDifferential Input Offset Voltagevs Temperature (Note 7)

Common Mode Offset Voltagevs Temperature

Applicable to all parts in the LTC1992 family.

TOTAL SUPPLY VOLTAGE (V)

0

SU

PP

LY

CU

RR

EN

T (

mA

)

0.6

0.8

1.0

8

1992 G01

0.4

0.2

0.5

0.7

0.9

0.3

0.1

021 43 6 7 95 10

125°C

85°C

25°C

–40°C

TEMPERATURE (°C)

–40

0.6

0.4

0.2

0

–0.2

–0.4

–0.6

–0.8

1992 G02

25 85 125

DIF

FER

EN

TIA

L V

OS (

mV

)

VINCM = 0VVOCM = 0V

VS = ±1.35V

VS = ±2.5V

VS = ±5V

TEMPERATURE (°C)

–40–5

CO

MM

ON

MO

DE V

OS (

mV

)

–4

–2

–1

0

85

4

1992 G03

–3

25 125

1

2

3

VINCM = 0VVOCM = 0V

VS = ±5V

VS = ±1.35V

VS = ±2.5V

VOCM VOLTAGE (V)

0–20

VO

CM

VO

S (

mV

)

–15

–5

0

5

0.6 1.2 1.5 2.7

1992 G04

–10

0.3 0.9 1.8 2.1 2.4

125°C

85°C

25°C

–40°C

+VS = 2.7V–VS = 0VVINCM = 1.35V

VOCM VOLTAGE (V)

0

VO

CM

VO

S (

mV

)

–5

0

5

4

1992 G05

–10

–15

–200.5 1 1.5 2 2.5 3 3.5 4.5 5

+VS = 5V–VS = 0VVINCM = 2.5V

125°C

85°C

25°C

–40°C

VOCM VOLTAGE (V)

–5

VO

CM

VO

S (

mV

)–5

0

5

3

1992 G06

–10

–15

–20–4 –3 –2 –1 0 1 2 4 5

+VS = 5V–VS = –5VVINCM = 0V

125°C

85°C25°C

–40°C

LOAD CURRENT (mA)

–20

+S

WIN

G (

V) –

SW

ING

(V)

2.50

2.60

20

1992 G07

2.40

2.30–10 0 10–15 –5 5 15

2.70

2.45

2.55

2.35

2.65

0.4

0.6

0.2

0

0.8

0.3

0.5

0.1

0.7

–40°C

–40°C

125°C

125°C

25°C

85°C

85°C

25°C

LOAD CURRENT (mA)

–20 204.50

+S

WIN

G (

V) –

SW

ING

(V)

4.55

4.65

4.70

4.75

5.00

4.85

–10 0

1992 G08

4.60

4.90

4.95

4.80

0

0.1

0.3

0.4

0.5

1.0

0.7

0.2

0.8

0.9

0.6

10 15–15 –5 5

–40°C

–40°C

125°C

125°C

85°C

85°C25°C

25°C

LTC1992 Family

81992fb


Differential Gain vs Time(Normalized to t = 0)

Input Common Mode Overdrive Recovery (Expanded View)

Input Common Mode Overdrive Recovery (Detailed View)

Output Overdrive Recovery(Expanded View)

Output Overdrive Recovery(Detailed View)

Output Voltage Swing vs Output Load, VS = ±5V

VOCM Input Bias Currentvs VOCM Voltage

Differential Input Offset Voltage vs Time (Normalized to t = 0)

Applicable to all parts in the LTC1992 family.

LOAD CURRENT (mA)

–204.4

+S

WIN

G (

V) –

SW

ING

(V)

4.5

4.6

4.7

4.8

–10 0 10 20–15 –5 5 15

1992 G09

4.9

5.0

–5.0

–4.8

–4.6

–4.4

–4.2

–4.0

–3.8

–40°C

–40°C

125°C

125°C85°C

25°C

85°C

25°C

VOCM VOLTAGE (V)

0 0.5 1

VO

CM

IN

PU

T B

IAS

CU

RR

EN

T (

A)

1.5 2 2.5 3 3.5 4 4.5 5

1992 G10

100E-15

10E-9

1E-9

100E-12

10E-12

1E-12+VS = 5V–VS = 0VVINCM = 2.5V

125°C

85°C

25°C–40°C

TIME (HOURS)

100

80

60

40

20

0

–20

–40

–60

–80

–100

DELTA

VO

S (

μV

)

1992 G11

0 400 800 1200 1600 2000

TEMP = 35°C

TIME (HOURS)

10

8

6

4

2

0

–2

–4

–6

–8

–10

DELT

A G

AIN

(ppm

)

1992 G12

0 400 800 1200 1600 2000

TEMP = 35°C

50μs/DIV

1V

/DIV

1992 G13

BOTH INPUTS(INPUTS TIEDTOGETHER)

OUTPUTS

+VS = 2.5V–VS = –2.5VVOCM = 0VLTC1992-10 SHOWNFOR REFERENCE

1μs/DIV

1V

/DIV

1992 G14

BOTH INPUTS(INPUTS TIED TOGETHER)

OUTPUTS


50μs/DIV

1V

/DIV

1992 G15

+VS = 2.5V, –VS = –2.5V, VOCM = 0V

OUTPUTSINPUTS

LTC1992-2 SHOWN FOR REFERENCE

5μs/DIV

1V

/DIV

1992 G16

INPUTS OUTPUTS


LTC1992 Family

91992fb


Differential Input Offset Voltage vs Input Common Mode Voltage



Common Mode Rejection Ratiovs Frequency (Note 7)

Power Supply Rejection Ratiovs Frequency (Note 7) Output Balance vs Frequency

Differential Input Differential Gain vs Frequency, VS = ±2.5V

Single-Ended Input Differential Gain vs Frequency, VS = ±2.5V

Differential Phase Response vs Frequency

Applicable to the LTC1992 only.

FREQUENCY (kHz)

10

–24

GA

IN (

dB

) –18

–12

–6

0

100 1000 10000

1992 G17

–30

–36

–42

–66

–60

–54

–48

6

12

CLOAD = 10000pFCLOAD = 5000pFCLOAD = 1000pFCLOAD = 500pFCLOAD = 100pFCLOAD = 50pFCLOAD = 10pF

RIN = RFB = 10k

FREQUENCY (kHz)

10

–24

GA

IN (

dB

) –18

–12

–6

0

100 1000 10000

1992 G18

–30

–36

–42

–66

–60

–54

–48

6

12


RIN = RFB = 10k

FREQUENCY (kHz)

10

PH

AS

E (

DEG

)

0

–20

–40

–60

–80

–100

–120

–140

–160

–180100 1000

1992 G37

CLOAD =10pF50pF100pF500pF1000pF5000pF10000pF

RIN = RFB = 10k

COMMON MODE VOLTAGE (V)

0

DIF

FER

EN

TIA

L V

OS (

mV

)

1922 G20

0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7

2.0

1.5

1.0

0.5

0

–0.5

–1.0

–1.5

–2.0

125°C

–40°C

25°C 85°C

+VS = 2.7V–VS = 0VVOCM = 1.35V


0 4.0

1922 G21

1.00.5 1.5 2.5 3.5 4.52.0 3.0 5.0

125°C

–40°C

85°C25°C

DIF

FER

EN

TIA

L V

OS (

mV

)

2.0

1.5

1.0

0.5

0

–0.5

–1.0

–1.5

–2.0

+VS = 5V–VS = 0VVOCM = 2.5V


–5 3

1922 G22

–3–4 –2 0 2 4–1 1 5

125°C

–40°C

85°C

DIF

FER

EN

TIA

L V

OS (

mV

)

2.0

1.5

1.0

0.5

0

–0.5

–1.0

–1.5

–2.0

25°C

+VS = 5V–VS = –5VVOCM = 0V

FREQUENCY (Hz)

40

CM

RR

(dB

)

80

120

20

60

100

100 10k 100k 1M

1992 G23

01k

ΔVAMPCM

ΔVAMPDIFF

FREQUENCY (Hz)

10

40PS

RR

(dB

)

50

60

70

80

100 1k 10k 100k 1M

1992 G24

30

20

10

0

90

100

–VS

+VS

ΔVS

ΔVAMPDIFF

FREQUENCY (Hz)

1 10

–40

OU

TP

UT B

ALA

NC

E (

dB

)

–60

–80

100 1k 10k 100k 1M

1992 G25

–20

0

–100

ΔVOUTCM

ΔVOUTDIFF

LTC1992 Family

101992fb


Single-Ended Input Large-Signal Step Response


Differential Input Small-Signal Step Response


Differential Input Large-Signal Step Response



2μs/DIV

VO

UTD

IFF

(1V

/DIV

)

1992 G26

+VS = 2.5V–VS = –2.5VVOCM = 0V+VIN = ±1.5V–VIN = 1.5VCLOAD = 0pFGAIN = 1

0V

±

20μs/DIV 1992 G27

+VS = 2.5V–VS = –2.5VVOCM = 0V+VIN = ±1.5V–VIN = 1.5VGAIN = 1

CLOAD = 10000pFCLOAD = 1000pF

VO

UTD

IFF

(1V

/DIV

)

0V

±

2μs/DIV

VO

UTD

IFF

(1V

/DIV

)

1992 G28

+VS = 5V–VS = 0VVOCM = 2.5V+VIN = 0V TO 4V–VIN = 2VCLOAD = 0pFGAIN = 1

2.5V

20μs/DIV

VO

UTD

IFF

(1V

/DIV

)

1992 G29

+VS = 5V–VS = 0VVOCM = 2.5V+VIN = 0V TO 4V–VIN = 2VGAIN = 1


2.5V

1μs/DIV

VO

UTD

IFF

(50m

V/D

IV)

1992 G30

+VS = 2.5V–VS = –2.5VVOCM = 0V+VIN = ±50mV–VIN = 50mVCLOAD = 0pFGAIN = 1

0V

±

10μs/DIV

VO

UTD

IFF

(50m

V/D

IV)

1992 G31

+VS = 2.5V–VS = –2.5VVOCM = 0V+VIN = ±50mV–VIN = 50mVGAIN = 1


0V

±

LTC1992 Family

111992fb


THD + Noise vs Frequency THD + Noise vs Amplitude

Differential Noise Voltage Densityvs Frequency

VOCM Gain vs Frequency, VS = ±2.5V

Single-Ended Input Small-Signal Step Response



FREQUENCY (kHz)

10

–15

GA

IN (

dB

)

–5

5

100 1000 10000

1992 G19

–25

–20

–10

0

–30

–35

CLOAD = 10pF TO 10000pF

1μs/DIV

VO

UTD

IFF

(50m

V/D

IV)

1992 G32

+VS = 5V–VS = 0VVOCM = 2.5V+VIN = 0V TO 200mV–VIN = 100mVCLOAD = 0pFGAIN = 1

2.5V

10μs/DIV

VO

UTD

IFF

(50m

V/D

IV)

1992 G33

+VS = 5V–VS = 0VVOCM = 2.5V+VIN = 0V TO 200mV–VIN = 100mVGAIN = 1


2.5V

FREQUENCY (Hz)

100–100

TH

D +

NO

ISE (

dB

)

–60

–50

–40

1k 10k 50k

1992 G34

–70

–80

–90

500kHz MEASUREMENT BANDWIDTH+VS = 5V–VS = –5VVOCM = 0V

VOUT = 1VP-PDIFF

VOUT = 2VP-PDIFF

VOUT = 10VP-PDIFF

VOUT = 5VP-PDIFF

INPUT SIGNAL AMPLITUDE (VP-PDIFF)

0.1–100

TH

D +

NO

ISE (

dB

)

–90

–80

–70

–60

–40

1 10 20

1992 G35

–50


50kHz20kHz

10kHz

5kHz

2kHz1kHz

FREQUENCY (Hz)

INP

UT R

EFE

RR

ED

NO

ISE (

nV

√H

z)

1000

100

10100 1000 10000

1922 G36

10

LTC1992 Family

121992fb





Differential Gain Error vs Temperature VOCM Gain vs Frequency




Applicable to the LTC1992-1 only.

FREQUENCY (kHz)

10

–24

GA

IN (

dB

) –18

–12

–6

0

100 1000 10000

1992 G38

–30

–36

–42

–66

–60

–54

–48

6

12


FREQUENCY (kHz)

10

–24

GA

IN (

dB

) –18

–12

–6

0

100 1000 10000

1992 G39

–30

–36

–42

–66

–60

–54

–48

6

12


FREQUENCY (kHz)

10

PH

AS

E (

DEG

)

0

–20

–40

–60

–80

–100

–120

–140

–160

–180100 1000

1992 G40


TEMPERATURE (°C)

–50

GA

IN E

RR

OR

(%

)

0.025

0.020

0.015

0.010

0.005

0

–0.005

–0.010

–0.015

–0.020

–0.0250 50 75

1992 G41

–25 25 100 125

FREQUENCY (kHz)

10

–15

GA

IN (

dB

)

–5

5

100 1000 10000

1992 G42

–25

–20

–10

0

–30

–35



0

DIF

FER

EN

TIA

L V

OS (

mV

)

1922 G43

0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7

5

4

3

2

1

0

–1

–2

–3

–4

–5

125°C

–40°C

85°C25°C

+VS = 2.7V–VS = 0VVOCM = 1.35V


0

1922 G44

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

125°C–40°C

85°C25°C

DIF

FER

EN

TIA

L V

OS (

mV

)

5

4

3

2

1

0

–1

–2

–3

–4

–5



–5

1922 G45

–4 –3 –2 –1 0 1 2 3 4 5

125°C

–40°C85°C

25°C

DIF

FER

EN

TIA

L V

OS (

mV

)

5

4

3

2

1

0

–1

–2

–3

–4

–5


LTC1992 Family

131992fb




Power Supply Rejection Ratiovs Frequency


Differential Input Small-Signal Step Response Output Balance vs Frequency



Common Mode Rejection Ratiovs Frequency


2μs/DIV

VO

UTD

IFF

(1V

/DIV

)

1992 G46

+VS = 2.5V–VS = –2.5VVOCM = 0V+VIN = ±1.5V–VIN = 1.5V CLOAD = 0pF

0V

±

20μs/DIV

VO

UTD

IFF

(1V

/DIV

)

1992 G47

+VS = 2.5V–VS = –2.5VVOCM = 0V+VIN = ±1.5V–VIN = 1.5V


0V

±

FREQUENCY (Hz)

30

CM

RR

(dB

)

90

100

20

10

80

50

70

60

40

100 10k 100k 1M

1992 G48

01k

ΔVAMPCM

ΔVAMPDIFF

2μs/DIV

VO

UTD

IFF

(1V

/DIV

)

1992 G49

+VS = 5V–VS = 0VVOCM = 2.5V+VIN = 0V TO 4V–VIN = 2VCLOAD = 0pF

2.5V

20μs/DIV

VO

UTD

IFF

(1V

/DIV

)

1992 G50

+VS = 5V–VS = 0VVOCM = 2.5V+VIN = 0V TO 4V–VIN = 2V


2.5V

FREQUENCY (Hz)

10

40PS

RR

(dB

)

50

60

70

80

100 1k 10k 100k 1M

1992 G51

30

20

10

0

90

100

–VS

+VS

ΔVS

ΔVAMPDIFF

1μs/DIV

VO

UTD

IFF

(50m

V/D

IV)

1992 G52

+VS = 2.5V–VS = –2.5VVOCM = 0V+VIN = ±50mV–VIN = 50mVCLOAD = 0pF

0V

±

10μs/DIV

VO

UTD

IFF

(50m

V/D

IV)

1992 G53

+VS = 2.5V–VS = –2.5VVOCM = 0V+VIN = ±50mV–VIN = 50mV


0V

±

FREQUENCY (Hz)

1 10

–40

OU

TP

UT B

ALA

NC

E (

dB

)

–60

–80

100 1k 10k 100k 1M

1992 G54

–20

0

–100

ΔVOUTCM

ΔVOUTDIFF

LTC1992 Family

141992fb




Differential Noise Voltage Density vs Frequency



1μs/DIV

VO

UTD

IFF

(50m

V/D

IV)

1992 G55

+VS = 5V–VS = 0VVOCM = 2.5V+VIN = 0V TO 200mV–VIN = 100mVCLOAD = 0pF

2.5V

10μs/DIV

VO

UTD

IFF

(50m

V/D

IV)

1992 G56

+VS = 5V–VS = 0VVOCM = 2.5V+VIN = 0V TO 200mV–VIN = 100mV


2.5V

FREQUENCY (Hz)

100 1000 10000

1922 G57

10

INP

UT R

EFE

RR

ED

NO

ISE (

nV

√H

z)

1000

100

10

FREQUENCY (Hz)

100–100

TH

D +

NO

ISE (

dB

)

–60

–50

–40

1k 10k 50k

1992 G58

–70

–80

–90


VOUT = 1VP-PDIFF

VOUT = 2VP-PDIFF

VOUT = 10VP-PDIFF

VOUT = 5VP-PDIFF


0.1–100

TH

D +

NO

ISE (

dB

)

–90

–80

–70

–60

–40

1 10 20

1992 G59

–50


50kHz20kHz

10kHz

5kHz

2kHz1kHz

LTC1992 Family

151992fb


Differential Gain Error vs Temperature

VOCM Gain vs Frequency, VS = ±2.5V

Differential Input Offset Voltage vs Input Common Mode Voltage(Note 7)







FREQUENCY (kHz)

10

–24

GA

IN (

dB

)

–18

–12

–6

0

100 1000 10000

1992 G60

–30

–36

–42

–66

–60

–54

–48

6

18

12


FREQUENCY (kHz)

10

–24

GA

IN (

dB

)

–18

–12

–6

0

100 1000 10000

1992 G61

–30

–36

–42

–66

–60

–54

–48

6

18

12


FREQUENCY (kHz)

10

PH

AS

E (

DEG

)

0

–20

–40

–60

–80

–100

–120

–140

–160

–180100 1000

1992 G62


TEMPERATURE (°C)

–50

GA

IN E

RR

OR

(%

)

0.05

0.04

0.03

0.02

0.01

0

–0.01

–0.02

–0.03

–0.04

–0.050 50 75

1992 G63

–25 25 100 125

FREQUENCY (kHz)

10

–10

GA

IN (

dB

)

–5

0

5

100 1000 10000

1992 G64

–15

–20

–25

–30



0

DIF

FER

EN

TIA

L V

OS (

mV

)

2.0

1.5

1.0

0.5

0

–0.5

–1.0

–1.5

–2.04.0

1992 G66

1.0 2.0 3.0 5.03.50.5 1.5 2.5 4.5

–40°C

125°C

25°C85°C



0

DIF

FER

EN

TIA

L V

OS (

mV

)

0

0.5

1.0

2.4

1992 G65

–0.5

–1.0

–2.00.6 1.2 1.80.3 2.70.9 1.5 2.1

–1.5

1.5

2.0+VS = 2.7V–VS = 0VVOCM = 1.35V

–40°C

25°C

125°C85°C


–5

DIF

FER

EN

TIA

L V

OS (

mV

)

2.0

1.5

1.0

0.5

0

–0.5

–1.0

–1.5

–2.03

1992 G67

–3 –1 1 52–4 –2 0 4

–40°C

125°C

25°C


85°C

LTC1992 Family

161992fb

TYPICAL PERFORMANCE CHARACTERISTICS Applicable to the LTC1992-2 only.



Power Supply Rejection Ratiovs Frequency (Note 7)






2μs/DIV 1992 G68


VO

UTD

IFF

(1V

/DIV

)

0V

±

20μs/DIV 1992 G69



VO

UTD

IFF

(1V

/DIV

)

0V

±

FREQUENCY (Hz)

30

CM

RR

(dB

)

90

100

20

10

80

50

70

60

40

100 10k 100k 1M

1992 G70

01k

ΔVAMPCM

ΔVAMPDIFF

2μs/DIV 1992 G71

+VS = 5V–VS = 0VVOCM = 2.5V+VIN = 0V TO 2V–VIN = 1VCLOAD = 0pF

VO

UTD

IFF

(1V

/DIV

)

2.5V

20μs/DIV

VO

UTD

IFF

(1V

/DIV

)

1992 G72

+VS = 5V–VS = 0VVOCM = 2.5V+VIN = 0V TO 2V–VIN = 1V


2.5V

FREQUENCY (Hz)

10

40PS

RR

(dB

)

50

60

70

80

100 1k 10k 100k 1M

1992 G73

30

20

10

0

90

100

–VS

+VS

ΔVS

ΔVAMPDIFF

2μs/DIV

VO

UTD

IFF

(50m

V/D

IV)

1992 G74


0V

±

20μs/DIV

VO

UTD

IFF

(50m

V/D

IV)

1992 G75



0V

±

FREQUENCY (Hz)

1 10

–40

OU

TP

UT B

ALA

NC

E (

dB

)

–60

–80

100 1k 10k 100k 1M

1992 G76

–20

0

–100

ΔVOUTCM

ΔVOUTDIFF

LTC1992 Family

171992fb







2μs/DIV

VO

UTD

IFF

(50m

V/D

IV)

1992 G77


2.5V

20μs/DIV

VO

UTD

IFF

(50m

V/D

IV)

1992 G78



2.5V

FREQUENCY (Hz)

100 1000 10000

1922 G79

10

INP

UT R

EFE

RR

ED

NO

ISE (

nV

√H

z)

1000

100

10

FREQUENCY (Hz)

100–100

TH

D +

NO

ISE (

dB

)

–60

–50

–40

1k 10k 50k

1992 G80

–70

–80

–90

VOUT = 1VP-PDIFF

VOUT = 2VP-PDIFF

VOUT = 10VP-PDIFF

VOUT = 5VP-PDIFF


0.1–100

TH

D +

NO

ISE (

dB

)

–90

–80

–70

–60

–40

1 10

1992 G81

–50

500kHz MEASUREMENT BANDWIDTH+VS = 5V–VS = –5VVOCM = 0V 50kHz

20kHz

10kHz

5kHz

2kHz

1kHz

LTC1992 Family

181992fb










FREQUENCY (kHz)

10

–24GA

IN (

dB

)

–18

–12

–6

0

100 1000 10000

1992 G82

–30

–36

–42

–60

–54

–48

6

24

12

30

18


FREQUENCY (kHz)

10

–24GA

IN (

dB

)

–18

–12

–6

0

100 1000 10000

1992 G83

–30

–36

–42

–60

–54

–48

6

24

12

30

18


FREQUENCY (kHz)

10

PH

AS

E (

DEG

)

0

–20

–40

–60

–80

–100

–120

–140

–160

–180100 1000

1992 G84

10pF50pF100pF500pF1000pF5000pF10000pF

CLOAD =

TEMPERATURE (°C)

–50

GA

IN E

RR

OR

(%

)

0.050

0.025

0

–0.025

–0.050

–0.075

–0.100

–0.125

–01.500 50 75

1992 G85

–25 25 100 125


0

DIF

FER

EN

TIA

L V

OS (

mV

)

1922 G87

0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7

2.0

1.5

1.0

0.5

0

–0.5

–1.0

–1.5

–2.0

125°C

–40°C

85°C25°C

+VS = 2.7V–VS = 0VVOCM = 1.35V

FREQUENCY (kHz)

10

–10

GA

IN (

dB

)

–5

0

5

100 1000 10000

1992 G86

–15

–20

–25

–30



0

1922 G88

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

125°C

–40°C

85°C25°C

DIF

FER

EN

TIA

L V

OS (

mV

)

2.0

1.5

1.0

0.5

0

–0.5

–1.0

–1.5

–2.0



–5

1922 G89

–4 –3 –2 –1 0 1 2 3 4 5

125°C

–40°C

25°C85°C

DIF

FER

EN

TIA

L V

OS (

mV

)

2.0

1.5

1.0

0.5

0

–0.5

–1.0

–1.5

–2.0


LTC1992 Family

191992fb










2μs/DIV

VO

UTD

IFF

(1V

/DIV

)

1992 G90

+VS = 2.5V–VS = –2.5VVOCM = 0V+VIN = ± 300mV–VIN = 300mVCLOAD = 0pF

0V

±

20μs/DIV 1992 G91

+VS = 2.5V–VS = –2.5VVOCM = 0V+VIN = ± 300mV–VIN = 300mV


VO

UTD

IFF

(1V

/DIV

)

0V

±

FREQUENCY (Hz)

30

CM

RR

(dB

)

90

100

20

10

80

50

70

60

40

100 10k 100k 1M

1992 G92

01k

ΔVAMPCM

ΔVAMPDIFF

2μs/DIV

VO

UTD

IFF

(1V

/DIV

)

1992 G93


2.5V

20μs/DIV 1992 G94



VO

UTD

IFF

(1V

/DIV

)

2.5V

FREQUENCY (Hz)

10

40PS

RR

(dB

)

50

60

70

80

100 10k 100k1k 1M

1992 G95

30

20

10

0

90

100

+VS

–VS

ΔVS

ΔVAMPDIFF

5μs/DIV

VO

UTD

IFF

(50m

V/D

IV)

1992 G96


0V

±

50μs/DIV

VO

UTD

IFF

(50m

V/D

IV)

1992 G97



0V

±

FREQUENCY (Hz)

1 10

–40

OU

TP

UT B

ALA

NC

E (

dB

)

–60

–80

100 1k 10k 100k 1M

1992 G98

–20

0

–100

ΔVOUTCM

ΔVOUTDIFF

LTC1992 Family

201992fb






5μs/DIV

VO

UTD

IFF

(50m

V/D

IV)

1992 G99


2.5V

50μs/DIV 1992 G100



VO

UTD

IFF

(50m

V/D

IV)

2.5V

FREQUENCY (Hz)

100 1000 10000

1922 G101

10

INP

UT R

EFE

RR

ED

NO

ISE (

nV

√H

z)

1000

100

10

FREQUENCY (Hz)

100–100

TH

D +

NO

ISE (

dB

)

–60

–50

–40

1k 10k 50k

1992 G102

–70

–80

–90

VOUT = 1VP-PDIFF

VOUT = 2VP-PDIFF

VOUT = 10VP-PDIFF

VOUT = 5VP-PDIFF



0.1–100

TH

D +

NO

ISE (

dB

)

–90

–80

–70

–60

–40

1 5

1992 G103

–50


50kHz

20kHz

10kHz

5kHz

2kHz

1kHz


LTC1992 Family

211992fb









FREQUENCY (kHz)

10

–30

GA

IN (

dB

)

–20

–10

0

10

100 1000 10000

1992 G104

–40

–50

–60

20

30

40


FREQUENCY (kHz)

10

–30

GA

IN (

dB

)–20

–10

0

10

100 1000 10000

1992 G105

–40

–50

–60

20

30

40


FREQUENCY (kHz)

10

PH

AS

E (

DEG

)

0

–20

–40

–60

–80

–100

–120

–140

–160

–180100 1000

1992 G106

10pF50pF100pF500pF1000pF5000pF10000pF

CLOAD =

TEMPERATURE (°C)

–50

GA

IN E

RR

OR

(%

)

0.050

0.025

0

–0.025

–0.050

–0.075

–0.100

–0.125

–0.150

–0.175

–0.2000 50 75

1992 G107

–25 25 100 125

FREQUENCY (kHz)10

–10

GAIN

(dB)

–5

0

5

100 1000 10000

1992 G108

–15

–20

–25

–30



0

1922 G109

0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7

125°C

–40°C

85°C25°C

DIF

FER

EN

TIA

L V

OS (

mV

)

2.0

1.5

1.0

0.5

0

–0.5

–1.0

–1.5

–2.0

+VS = 2.7V–VS = 0VVOCM = 1.35V


0

1922 G110

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

125°C

–40°C

85°C25°C

DIF

FER

EN

TIA

L V

OS (

mV

)

2.0

1.5

1.0

0.5

0

–0.5

–1.0

–1.5

–2.0



–5

1922 G111

–4 –3 –2 –1 0 1 2 3 4 5

125°C

–40°C

85°C25°C

DIF

FER

EN

TIA

L V

OS (

mV

)

2.0

1.5

1.0

0.5

0

–0.5

–1.0

–1.5

–2.0


LTC1992 Family

221992fb










2μs/DIV 1992 G112


VO

UTD

IFF

(1V

/DIV

)

0V

±

20μs/DIV

VO

UTD

IFF

(1V

/DIV

)

1992 G113



0V

±

FREQUENCY (Hz)

30

CM

RR

(dB

)

90

100

20

10

80

50

70

60

40

100 10k 100k 1M

1992 G114

01k

ΔVAMPCM

ΔVAMPDIFF

2μs/DIV 1992 G115


VO

UTD

IFF

(1V

/DIV

)

2.5V

20μs/DIV

VO

UTD

IFF

(1V

/DIV

)

1992 G116



2.5V

FREQUENCY (Hz)

10

40PS

RR

(dB

)

50

60

70

80

100 10k 100k1k 1M

1992 G117

30

20

10

0

90

100

+VS

–VS

ΔVS

ΔVAMPDIFF

10μs/DIV 1992 G118


VO

UTD

IFF

(50m

V/D

IV)

0V

±

100μs/DIV

VO

UTD

IFF

(50m

V/D

IV)

1992 G119



0V

±

FREQUENCY (Hz)

1 10

–60

OU

TP

UT B

ALA

NC

E (

dB

)

100 1k 10k 100k 1M

1992 G120

–40

–20

0

–80

–100

–120

ΔVOUTCM

ΔVOUTDIFF

LTC1992 Family

231992fb






10μs/DIV 1992 G121


VO

UTD

IFF

(50m

V/D

IV)

2.5V

100μs/DIV

VO

UTD

IFF

(50m

V/D

IV)

1992 G122



2.5V

FREQUENCY (Hz)

100 1000 10000

1922 G123

10

INP

UT R

EFE

RR

ED

NO

ISE (

nV

√H

z)

1000

100

10

FREQUENCY (Hz)

100–100

TH

D +

NO

ISE (

dB

)

–60

–50

–40

1k 10k 50k

1992 G124

–70

–80

–90

VOUT = 1VP-PDIFF

VOUT = 2VP-PDIFF

VOUT = 5VP-PDIFF



0.1–100

TH

D +

NO

ISE (

dB

)

–90

–80

–70

–60

–40

1 2

1992 G125

–5050kHz

20kHz

10kHz

5kHz

2kHz

1kHz

LTC1992 Family

241992fb

PIN FUNCTIONS–IN, +IN (Pins 1, 8): Inverting and Noninverting Inputs of the Amplifier. For the LTC1992 part, these pins are connected directly to the amplifier’s P-channel MOSFET input devices. The fixed gain LTC1992-X parts have preci-sion, on-chip gain setting resistors. The input resistors are nominally 30k for the LTC1992-1, LTC1992-2 and LTC1992-5 parts. The input resistors are nominally 15k for the LTC1992-10 part.

VOCM (Pin 2): Output Common Mode Voltage Set Pin. The voltage on this pin sets the output signal’s common mode voltage level. The output common mode level is set independent of the input common mode level. This is a high impedance input and must be connected to a known and controlled voltage. It must never be left floating.

+VS, –VS (Pins 3, 6): The +VS and –VS power supply pins should be bypassed with 0.1μF capacitors to an adequate ana-log ground or ground plane. The bypass capacitors should be located as closely as possible to the supply pins.

+OUT, –OUT (Pins 4, 5): The Positive and Negative Outputs of the Amplifier. These rail-to-rail outputs are designed to drive capacitive loads as high as 10,000pF.

VMID (Pin 7): Mid-Supply Reference. This pin is connected to an on-chip resistive voltage divider to provide a mid-supply reference. This provides a convenient way to set the output common mode level at half-supply. If used for this purpose, Pin 2 will be shorted to Pin 7, Pin 7 should be bypassed with a 0.1μF capacitor to ground. If this refer-ence voltage is not used, leave the pin floating.

BLOCK DIAGRAMS (1992)

+

–

1

7

2

6

3

8

5

4

+

–200k

200k

+VS

–VS

V+

V–

30k

30k

A1

+

+

+

–

A2

+OUT

1992 BD

–IN

VMID

VOCM

+IN

–OUT

+VS

–VS

+VS

–VS

LTC1992 Family

251992fb

BLOCK DIAGRAMS (1992-X)

–

–

+

+

+VS

+VS

–IN

VMID

+IN

–VS

+VS

–VS

–VS

+OUT

–OUT

VOCM

200k

200k

RIN RFB

RIN RFB

4

5

26

1

3

7

8

1992-X BD

PART

LTC1992-1LTC1992-2LTC1992-5LTC1992-10

RIN

30k30k30k15k

RFB

30k60k150k150k

APPLICATIONS INFORMATIONTheory of Operation

The LTC1992 family consists of five fully differential, low power amplifiers. The LTC1992 is an unconstrained fully differential amplifier. The LTC1992-1, LTC1992-2, LTC1992-5 and LTC1992-10 are fixed gain blocks (with gains of 1, 2, 5 and 10 respectively) featuring precision on-chip resistors for accurate and ultra stable gain.

In many ways, a fully differential amplifier functions much like the familiar, ubiquitous op amp. However, there are several key areas where the two differ. Referring to Figure 1, an op amp has a differential input, a high open-loop gain and utilizes negative feedback (through resistors) to set the closed-loop gain and thus control the amplifier’s gain with great precision. A fully differential amplifier has all of these features plus an additional input and a complemen-tary output. The complementary output reacts to the input signal in the same manner as the other output, but in the opposite direction. Two outputs changing in an equal but opposite manner require a common reference point (i.e., opposite relative to what?). The additional input, the VOCM pin, sets this reference point. The voltage on the VOCM input directly sets the output signal’s common mode voltage and

allows the output signal’s common mode voltage to be set completely independent of the input signal’s common mode voltage. Uncoupling the input and output common mode voltages makes signal level shifting easy.

For a better understanding of the operation of a fully dif-ferential amplifier, refer to Figure 2. Here, the LTC1992 functional block diagram adds external resistors to real-ize a basic gain block. Note that the LTC1992 functional block diagram is not an exact replica of the LTC1992 circuitry. However, the Block Diagram is correct and is a very good tool for understanding the operation of fully differential amplifier circuits. Basic op amp fundamentals together with this block diagram provide all of the tools needed for understanding fully differential amplifier circuit applications.

The LTC1992 Block Diagram has two op amps, two sum-ming blocks (pay close attention the signs) and four resis-tors. Two resistors, RMID1 and RMID2, connect directly to the VMID pin and simply provide a convenient mid-supply reference. Its use is optional and it is not involved in the operation of the LTC1992’s amplifier. The LTC1992 functions through the use of two servo networks each employing

LTC1992 Family

261992fb

APPLICATIONS INFORMATION

Figure 1. Comparison of an Op Amp and a Fully Differential Amplifier

Figure 2. LTC1992 Functional Block Diagram with External Gain Setting Resistors

–

–+

+

–

–+

+

1992 F01

RIN

RIN

RFB

RFB

Fully Differential Amplifier with Negative Feedback

Fully Differential Amplifier

–VIN

+VIN

VOCM

VOCM

VOCM

–VOUT

+VOUT–

+

RIN

RFB

Op Amp with Negative Feedback

VIN

VOUT

RFB

RINGAIN = –

RFB

RINGAIN = –

+OUT

• DIFFERENTIAL INPUT• HIGH OPEN-LOOP GAIN• DIFFERENTIAL OUTPUT• VOCM INPUT SETS OUTPUT COMMON MODE LEVEL

–OUT

–IN

+IN

VOCM

–

+

Op Amp

OUTLTC1992AO

LTC1992AO

LTC1992LTC1992

• DIFFERENTIAL INPUT• HIGH OPEN-LOOP GAIN• SINGLE-ENDED OUTPUT

–IN

+IN

+

–

7

2

6

3

+

–

RMID1200k

RMID2200k

INP

INM

V+

V–

RCMP30k

RCMM30k

A1

SP

LTC1992

SM

+

+

+

–

A2

+OUT

1992 F02

–IN+VIN

–VIN

RIN

RFB

RIN

VMID

VOCM

+IN

–OUT–VOUT

+VOUT

+VS

–VS

5

4

RFB

1

8

LTC1992 Family

271992fb

APPLICATIONS INFORMATIONnegative feedback and using an op amp’s differential input to create the servo’s summing junction.

One servo controls the signal gain path. The differential input of op amp A1 creates the summing junction of this servo. Any voltage present at the input of A1 is amplified (by the op amp’s large open-loop gain), sent to the summing blocks and then onto the outputs. Taking note of the signs on the summing blocks, op amp A1’s output moves +OUT and –OUT in opposite directions. Applying a voltage step at the INM node increases the +OUT voltage while the –OUT voltage decreases. The RFB resistors connect the outputs to the appropriate inputs establishing negative feedback and closing the servo’s loop. Any servo loop always attempts to drive its error voltage to zero. In this servo, the error voltage is the voltage between the INM and INP nodes, thus A1 will force the voltages on the INP and INM nodes to be equal (within the part’s DC offset, open loop gain and bandwidth limits). The “virtual short” between the two inputs is conceptually the same as that for op amps and is critical to understanding fully differential amplifier applications.

The other servo controls the output common mode level. The differential input of op amp A2 creates the summing junction of this servo. Similar to the signal gain servo above, any voltage present at the input of A2 is amplified, sent to the summing blocks and then onto the outputs. However, in this case, both outputs move in the same direc-tion. The resistors RCMP and RCMM connect the +OUT and –OUT outputs to A2’s inverting input establishing negative feedback and closing the servo’s loop. The midpoint of resistors RCMP and RCMM derives the output’s common mode level (i.e., its average). This measure of the output’s common mode level connects to A2’s inverting input while A2’s noninverting input connects directly to the VOCM pin. A2 forces the voltages on its inverting and noninverting inputs to be equal. In other words, it forces the output common mode voltage to be equal to the voltage on the VOCM input pin.

For any fully differential amplifier application to function properly both the signal gain servo and the common mode level servo must be satisfied. When analyzing an applica-tions circuit, the INP node voltage must equal the INM node voltage and the output common mode voltage must equal

the VOCM voltage. If either of these servos is taken out of the specified areas of operation (e.g., inputs taken beyond the common mode range specifications, outputs hitting the supply rails or input signals varying faster than the part can track), the circuit will not function properly.

Fully Differential Amplifier Signal Conventions

Fully differential amplifiers have a multitude of signals and signal ranges to consider. To maintain proper operation with conventional op amps, the op amp’s inputs and its output must not hit the supply rails and the input signal’s common mode level must also be within the part’s speci-fied limits. These considerations also apply to fully dif-ferential amplifiers, but here there is an additional output to consider and common mode level shifting complicates matters. Figure 3 provides a list of the many signals and specifications as well as the naming convention. The phrase “common mode” appears in many places and often leads to confusion. The fully differential amplifier’s ability to uncouple input and output common mode levels yields great design flexibility, but also complicates matters some. For simplicity, the equations in Figure 3 also assume an ideal amplifier and perfect resistor matching. For a detailed analysis, consult the fully differential amplifier applications circuit analysis section.

Basic Applications Circuits

Most fully differential amplifier applications circuits employ symmetrical feedback networks and are familiar territory for op amp users. Symmetrical feedback networks require that the –VIN/+VOUT network is a mirror image duplicate of the +VIN/–VOUT network. Each of these half circuits is basi-cally just a standard inverting gain op amp circuit. Figure 4 shows three basic inverting gain op amp circuits and their corresponding fully differential amplifier cousins. The vast majority of fully differential amplifier circuits derive from old tried and true inverting op amp circuits. To create a fully differential amplifier circuit from an inverting op amp circuit, first simply transfer the op amp’s VIN/VOUT network to the fully differential amplifier’s –VIN/+VOUT nodes. Then, take a mirror image duplicate of the network and apply it to the fully differential amplifier’s +VIN/–VOUT nodes. Op amp users can comfortably transfer any inverting op amp circuit to a fully differential amplifier in this manner.

LTC1992 Family

281992fb

Single-Ended to Differential Conversion

One of the most important applications of fully differential amplifiers is single-ended signaling to differential signaling conversion. Many systems have a single-ended signal that must connect to an ADC with a differential input. The ADC could be run in a single-ended manner, but performance usually degrades. Fortunately, all of basic applications circuits shown in Figure 4, as well as all of the fixed gain LTC1992-X parts, are equally suitable for both differential and single-ended input signals. For single-ended input signals, connect one of the inputs to a reference voltage (e.g., ground or mid-supply) and connect the other to the signal path. There are no tradeoffs here as the part’s performance is the same with single-ended or differential

input signals. Which input is used for the signal path only affects the polarity of the differential output signal.

Signal Level Shifting

Another important application of fully differential ampli-fier is signal level shifting. Single-ended to differential conversion accompanied by a signal level shift is very commonplace when driving ADCs. As noted in the theory of operation section, fully differential amplifiers have a com-mon mode level servo that determines the output common mode level independent of the input common mode level. To set the output common mode level, simply apply the desired voltage to the VOCM input pin. The voltage range on the VOCM pin is from (–VS + 0.5V) to (+VS – 1.3V).

Figure 3. Fully Differential Amplifier Signal Conventions (Ideal Amplifier and Perfect Resistor Matching is Assumed)

–

–+

+

1992 F03

RIN

RIN

RFB

VOCMVOCM

RFB

B

B

–B

–B

–VIN

–A

–A

VINCM VOUTCMVINDIFF

4AVP-PDIFFA

A

+VIN

2AVP-P

2AVP-P

= VINDIFF = +VIN – –VIN

2BVP-P

2BVP-P

DIFFERENTIAL

INPUT VOLTAGE

= VINCM = INPUT COMMON

MODE VOLTAGE

+VOUT = • • + VOCM ; VOSCM = 0V +VIN – –VIN

+VIN + –VIN2

= VOUTDIFF = +VOUT – –VOUTDIFFERENTIAL

OUTPUT VOLTAGE

–VOUT

+VOUT

LTC1992 VOUTDIFF4BVP-PDIFF

1

2

RFBRIN

= VOUTCM = OUTPUT COMMON

MODE VOLTAGE

+VOUT + –VOUT2

( )–VOUT = • • + VOCM ; VOSCM = 0V –VIN – +VIN

1

2

RFBRIN

VOUTDIFF = VINDIFF • RFBRIN

rN ≈ (0.13nV/√Hz)

VAMPCM = VINP + VINM

2

CMRR = ; +VIN = –VINΔVAMPCMΔVAMPDIFF

OUTPUT BALANCE = ΔVOUTCMΔVOUTDIFF

eNOUT = WHERE: eNOUT = OUTPUT REFERRED NOISE VOLTAGE DENSITY

eNIN = INPUT REFERRED NOISE VOLTAGE DENSITY

(RESISTIVE NOISE IS ALREADY INCLUDED IN THE

SPECIFICATIONS FOR THE FIXED GAIN LTC1992-X PARTS)

+ 1RFBRIN

VOUTCM = VOCM

VAMPDIFF = VINP – VINM

VOSCM = VOUTCM – VOCM

( )

( )

VOSDIFFOUT = VOSDIFFIN • + 1RFBRIN( )

INM

INP

RIN • RFBRIN + RFB( )

• √eNIN2 + rN

2


LTC1992 Family

291992fb


Figure 4. Basic Fully Differential Amplifier Application Circuits (Note: Single-Ended to Differential Conversion is Easily Accomplished by Connecting One of the Input Nodes, +VIN or –VIN, to a DC Reference Level (e.g., Ground))

–

–+

+RIN

RIN

RFB

RFB

Gain Block

–VIN

+VIN

VOCM

–VOUT

+VOUT–

+

RIN

VIN

RFB

VOUT

RFB

RINGAIN =

LTC1992

–

–+

+RIN

RIN

RFB

RFB

AC Coupled Gain Block

–VIN

+VIN

VOCM

–VOUT

+VOUT–

+

RINCIN CIN

CIN

VIN

RFB

VOUT LTC1992

–

–+

+RIN

RIN

RFB

RFB

Single Pole Lowpass Filter

–VIN

+VIN

RFBRIN

P

S + P

; P =

VOCM

–VOUT

+VOUT–

+

RIN

VIN

RFB

C

VOUT

H(S) = HO •

WHERE HO =

LTC1992

C

C1

RFB • C

–

–+

+R1 R3

R3

R4

R4R1

R2

R23-Pole Lowpass Filter

–VIN

+VIN

R2

R1; P = ; O =

VOCM

–VOUT

1992 F04

+VOUT–

+

R1 R3

R4

R2

C1

C2VOUT

WHERE HO =

LTC1992

C3

C1

C1

1

R4C3

1

R2R3C1C2

C2

2

C3

2

P

S + PH(S) = HO ( ) O

2

S2 + S +O

Q O2( )

VIN

RFBRIN

; P = HO = 1

RIN • CIN

S

S + PH(S) = HO •

C2

C1

R1 • √R2R3

R1 R2 + R1 R2 + R2 R3•Q =

LTC1992 Family

301992fb

APPLICATIONS INFORMATIONThe VOCM input pin has a very high input impedance and is easily driven by even the weakest of sources. Many ADCs provide a voltage reference output that defines either its common mode level or its full-scale level. Apply the ADC’s reference potential either directly to the VOCM pin or through a resistive voltage divider depending on the reference voltage’s definition. When controlling the VOCM pin by a high impedance source, connect a bypass capacitor (1000pF to 0.1μF) from the VOCM pin to ground to lower the high frequency impedance and limit external noise coupling. Other applications will want the output biased at a midpoint of the power supplies for maximum output voltage swing. For these applications, the LTC1992 provides a mid-supply potential at the VMID pin. The VMID pin connects to a simple resistive voltage divider with two 200k resistors connected between the supply pins. To use this feature, connect the VMID pin to the VOCM pin and bypass this node with a capacitor.

One undesired effect of utilizing the level shifting function is an increase in the differential output offset voltage due to gain setting resistor mismatch. The offset is approximately the amount of level shift (VOUTCM – VINCM) multiplied by the amount of resistor mismatch. For example, a 2V level shift with 0.1% resistors will give around 2mV of output offset (2 • 0.1% = 2mV). The exact amount of offset is dependent on the application’s gain and the resistor mismatch. For a detail description, consult the Fully Differential Amplifier Applications Circuit Analysis section.

CMRR and Output Balance

One common misconception of fully differential amplifiers is that the common mode level servo guarantees an infinite common mode rejection ratio (CMRR). This is not true. The common mode level servo does, however, force the two outputs to be truly complementary (i.e., exactly opposite or 180 degrees out of phase). Output balance is a measure of how complementary the two outputs are.

At low frequencies, CMRR is primarily determined by the matching of the gain setting resistors. Like any op amp, the LTC1992 does not have infinite CMRR, however resistor mismatching of only 0.018%, halves the circuit’s CMRR. Standard 1% tolerance resistors yield a CMRR of about 40dB. For most applications, resistor matching dominates

low frequency CMRR performance. The specifications for the fixed gain LTC1992-X parts include the on-chip resistor matching effects. Also, note that an input common mode signal appears as a differential output signal reduced by the CMRR. As with op amps, at higher frequencies the CMRR degrades. Refer to the Typical Performance plots for the details of the CMRR performance over frequency.

At low frequencies, the output balance specification is determined by the matching of the on-chip RCMM and RCMP resistors. At higher frequencies, the output bal-ance degrades. Refer to the typical performance plots for the details of the output balance performance over frequency.

Input Impedance

The input impedance for a fully differential amplifier ap-plication circuit is similar to that of a standard op amp inverting amplifier. One major difference is that the input impedance is different for differential input signals and single-ended signals. Referring to Figure 3, for differential input signals the input impedance is expressed by the following expression:

RINDIFF = 2 • RIN

For single-ended signals, the input impedance is expressed by the following expression:

RINS-E = RIN

1–RFB

2 • RIN + RFB( )

The input impedance for single-ended signals is slightly higher than the RIN value since some of the input signal is fed back and appears as the amplifier’s input common mode level. This small amount of positive feedback in-creases the input impedance.

Driving Capacitive Loads

The LTC1992 family of parts is stable for all capacitive loads up to at least 10,000pF. While stability is guaranteed, the part’s performance is not unaffected by capacitive load-ing. Large capacitive loads increase output step response ringing and settling time, decrease the bandwidth and increase the frequency response peaking. Refer to the

LTC1992 Family

311992fb

APPLICATIONS INFORMATIONTypical Performance plots for small-signal step response, large-signal step response and gain over frequency to appraise the effects of capacitive loading. While the con-sequences are minor in most instances, consider these effects when designing application circuits with large capacitive loads.

Input Signal Amplitude Considerations

For application circuits to operate correctly, the amplifier must be in its linear operating range. To be in the linear operating range, the input signal’s common mode voltage must be within the part’s specified limits and the rail-to-rail outputs must stay within the supply voltage rails. Addition-ally, the fixed gain LTC1992-X parts have input protection diodes that limit the input signal to be within the supply voltage rails. The unconstrained LTC1992 uses external resistors allowing the source signals to go beyond the supply voltage rails.

When taken outside of the linear operating range, the circuit does not perform as expected, however nothing extreme occurs. Outputs driven into the supply voltage rails are simply clipped. There is no phase reversal or oscillation. Once the outputs return to the linear operating range, there is a small recovery time, then normal opera-tion proceeds. When the input common mode voltage is below the specified lower limit, on-chip protection diodes conduct and clamp the signal. Once the signal returns to the specified operating range, normal operation proceeds. If the input common mode voltage goes slightly above the specified upper limit (by no more than about 500mV), the amplifier’s open-loop gain reduces and DC offset and closed-loop gain errors increase. Return the input back to the specified range and normal performance commences. If taken well above the upper limit, the amplifier’s input stage is cut off. The gain servo is now open loop; however, the common mode servo is still functional. Output bal-ance is maintained and the outputs go to opposite supply rails. However, which output goes to which supply rail is

random. Once the input returns to the specified input common mode range, there is a small recovery time then normal operation proceeds.

The LTC1992’s input signal common mode range (VINCMR) is from (–VS – 0.1V) to (+VS – 1.3V). This specification applies to the voltage at the amplifier’s input, the INP and INM nodes of Figure 2. The specifications for the fixed gain LTC1992-X parts reflect a higher maximum limit as this specification is for the entire gain block and references the signal at the input resistors. Differential input signals and single-ended signals require a slightly different set of formulae. Differential signals separate very nicely into common mode and differential components while single ended signals do not. Refer to Figure 5 for the formulae for calculating the available signal range. Additionally, Table 1 lists some common configurations and their ap-propriate signal levels.

The LTC1992’s outputs allow rail-to-rail signal swings. The output voltage on either output is a function of the input signal’s amplitude, the gain configured and the output signal’s common mode level set by the VOCM pin. For maximum signal swing, the VOCM pin is set at the midpoint of the supply voltages. For other applications, such as an ADC driver, the required level must fall within the VOCM range of (–VS + 0.5V) to (+VS – 1.3V). For single-ended input signals, it is not always obvious which output will clip first thus both outputs are calculated and the minimum value determines the signal limit. Refer to Figure 5 for the formula and Table 1 for examples.

To ensure proper linear operation both the input common mode level and the output signal level must be within the specified limits. These same criteria are also present with standard op amps. However, with a fully differential amplifier, it is a bit more complex and old familiar op amp intuition often leads to the wrong result. This is especially true for single-ended to differential conversion with level shifting. The required calculations are a bit tedious, but are necessary to guarantee proper linear operation.

LTC1992 Family

321992fb


Figure 5. Input Signal Limitations

–

–+

+RIN

INM

NODE

INP

NODE

RIN

RFB

VOCMVOCM

A. CALCULATE VINCM MINIMUM AND MAXIMUM GIVEN RIN, RFB AND VOCM

VINCM(MAX) = (+VS – 1.3V) + (+VS – 1.3V – VOCM)

VINCM(MIN) = (–VS – 0.1V) + (–VS – 0.1V – VOCM)

B. WITH A KNOWN VINCM, RIN, RFB AND VOCM, CALCULATE COMMON MODE VOLTAGE AT INP AND INM NODES (VINCM(AMP)) AND CHECK THAT IT IS WITHIN THE SPECIFIED LIMITS.

VINCM(AMP) = = VINCM + VOCM

RFB

B

B

–B

–B

–VIN

–A

–A

VINCM VOUTCMVINDIFF

4AVP-PDIFFA

A

+VIN

2AVP-P

2AVP-P

2BVP-P

2BVP-P–VOUT

+VOUT


1

G

1

G

4

G

4

G

VINP + VINM2

G

G + 1

1

G + 1

Differential Input Signals

–

–+

+

1992 F05

RIN

INM

NODE

INP

NODE

RIN

RFB

VOCMVOCM

RFB

B

B

–B

–B

VINREF

–A

VOUTCM

VREF

AVINSIG2AVP-P

2BVP-P

2BVP-P–VOUT

+VOUT


Single-Ended Input Signals

INPUT COMMON MODE LIMITS

OUTPUT SIGNAL CLIPPING LIMIT

INPUT COMMON MODE LIMITS (NOTE: FOR THE FIXED GAIN LTC1992-X PARTS, VINREF AND VINSIG CANNOT EXCEED THE SUPPLIES)

OUTPUT SIGNAL CLIPPING LIMIT

OR

OR

VINDIFF(MAX)(VP-PDIFF) = THE LESSER VALUE OF (+VS – VOCM) OR (VOCM – –VS)

VINREF

21

GVINSIG(MAX) = 2

VINSIG(MAX) = THE LESSER VALUE OF VINREF + (+VS – VOCM) OR VINREF + (VOCM – –VS)

+VS – 1.3V – +VS – 1.3V – VOCM+( () )VINREF

21

GVINSIG(MIN) = 2 –VS – 0.1V – –VS – 0.1V – VOCM+( () )

1

G

2

G

2

G

VINSIG(MIN) = THE GREATER VALUE OF VINREF + (–VS – VOCM) OR VINREF + (VOCM – +VS) 2

G

2

G

VINSIGP-P = 2 (+VS – –VS) – 1.2V (+VS – –VS) – 1.2V+( () )

RFBRIN

G =

RFBRIN

G =

LTC1992 Family

331992fb

APPLICATIONS INFORMATIONTable 1. Input Signal Limitations for Some Common Applications

Differential Input Signal, VOCM at Typical ADC Levels. (VINCM must be within the Min and Max table values and VINDIFF must be less than the table value)

+VS

(V)

–VS

(V)

GAIN

(V/V)

VOCM

(V)

VINCM(MAX)

(V)

VINCM(MIN)

(V)

VINDIFF(MAX)

(VP-PDIFF)

VOUTDIFF(MAX)

(VP-PDIFF)

2.7 0 1 1 1.800 –1.200 4.00 4.00

2.7 0 2 1 1.600 –0.650 2.00 4.00

2.7 0 5 1 1.480 –0.320 0.80 4.00

2.7 0 10 1 1.440 –0.210 0.40 4.00

5 0 1 2 5.400 –2.200 8.00 8.00

5 0 2 2 4.550 –1.150 4.00 8.00

5 0 5 2 4.040 –0.520 1.60 8.00

5 0 10 2 3.870 –0.310 0.80 8.00

5 –5 1 2 5.400 –12.200 12.00 12.00

5 –5 2 2 4.550 –8.650 6.00 12.00

5 –5 5 2 4.040 –6.520 2.40 12.00

5 –5 10 2 3.870 –5.810 1.20 12.00

Differential Input Signal, VOCM at Mid-Supply. (VINCM must be within the Min and Max table values and VINDIFF must be less than the table value)

+VS

(V)

–VS

(V)

GAIN

(V/V)

VOCM

(V)

VINCM(MAX)

(V)

VINCM(MIN)

(V)

VINDIFF(MAX)

(VP-PDIFF)

VOUTDIFF(MAX)

(VP-PDIFF)

2.7 0 1 1.35 1.450 –1.550 5.40 5.40

2.7 0 2 1.35 1.425 –0.825 2.70 5.40

2.7 0 5 1.35 1.410 –0.390 1.08 5.40

2.7 0 10 1.35 1.405 –0.245 0.54 5.40

5 0 1 2.5 4.900 –2.700 10.00 10.00

5 0 2 2.5 4.300 –1.400 5.00 10.00

5 0 5 2.5 3.940 –0.620 2.00 10.00

5 0 10 2.5 3.820 –0.360 1.00 10.00

5 –5 1 0 7.400 –10.200 20.00 20.00

5 –5 2 0 5.550 –7.650 10.00 20.00

5 –5 5 0 4.440 –6.120 4.00 20.00

5 –5 10 0 4.070 –5.610 2.00 20.00

LTC1992 Family

341992fb

APPLICATIONS INFORMATIONTable 1. Input Signal Limitations for Some Common Applications

+VS(V)

–VS(V)

GAIN(V/V)

VOCM(V)

VINREF(V)

VINSIG(MAX)(V)

VINSIG(MIN)(V)

VINSIGP-P(MAX)(VP-P AROUND VINREF)

VOUTDIFF(MAX)(VP-PDIFF)

2.7 0 1 1.35 1.35 1.550 –1.350 0.40 0.40

2.7 0 2 1.35 1.35 1.500 0.000 0.30 0.60

2.7 0 5 1.35 1.35 1.470 0.810 0.24 1.20

2.7 0 10 1.35 1.35 1.460 1.080 0.22 2.20

5 0 1 2.5 2.5 7.300 –2.500 9.60 9.60

5 0 2 2.5 2.5 5.000 0.000 5.00 10.00

5 0 5 2.5 2.5 3.500 1.500 2.00 10.00

5 0 10 2.5 2.5 3.000 2.000 1.00 10.00

5 –5 1 0 0 10.000 –10.000 20.00 20.00

5 –5 2 0 0 5.000 –5.000 10.00 20.00

5 –5 5 0 0 2.000 –2.000 4.00 20.00

5 –5 10 0 0 1.000 –1.000 2.00 20.00

Mid-Supply Referenced Single-Ended Input Signal, VOCM at Mid-Supply. (The VINSIG Min and Max values listed account for both the input common mode limits and the output clipping)

+VS(V)

–VS(V)

GAIN(V/V)

VOCM(V)

VINREF(V)

VINSIG(MAX)(V)

VINSIG(MIN)(V)



2.7 0 1 1 1.35 2.250 –0.650 1.80 1.80

2.7 0 2 1 1.35 1.850 0.350 1.00 2.00

2.7 0 5 1 1.35 1.610 0.950 0.52 2.60

2.7 0 10 1 1.35 1.530 1.150 0.36 3.60

5 0 1 2 2.5 6.500 –1.500 8.00 8.00

5 0 2 2 2.5 4.500 0.500 4.00 8.00

5 0 5 2 2.5 3.300 1.700 1.60 8.00

5 0 10 2 2.5 2.900 2.100 0.80 8.00

5 –5 1 2 0 6.000 –6.000 12.00 12.00

5 –5 2 2 0 3.000 –3.000 6.00 12.00

5 –5 5 2 0 1.200 –1.200 2.40 12.00

5 –5 10 2 0 0.600 –0.600 1.20 12.00

Mid-Supply Referenced Single-Ended Input Signal, VOCM at Typical ADC Levels. (The VINSIG Min and Max values listed account for both the input common mode limits and the output clipping)

LTC1992 Family

351992fb


Fully Differential Amplifier Applications Circuit Analysis

All of the previous applications circuit discussions have as-sumed perfectly matched symmetrical feedback networks. To consider the effects of mismatched or asymmetrical feedback networks, the equations get a bit messier.

Figure 6 lists the basic gain equation for the differential output voltage in terms of +VIN, –VIN, VOSDIFF, VOUTCM and the feedback factors β1 and β2. The feedback factors are simply the portion of the output that is fed back to the input summing junction by the RFB-RIN resistive voltage divider. β1 and β2 have the range of zero to one. The VOUTCM term also includes its offset voltage, VOSCM, and its gain mismatch term, KCM. The KCM term is determined by the matching of the on-chip RCMP and RCMM resistors in the common mode level servo (see Figure 2).

While mathematically correct, the basic signal equation does not immediately yield any intuitive feel for fully differential amplifier application operation. However, by nulling out specific terms, some basic observations and sensitivities come forth. Setting β1 equal to β2, VOSDIFF to zero and VOUTCM to VOCM gives the old gain equation from Figure 3. The ground referenced, single-ended input signal equation yields the interesting result that the driven side feedback factor (β1) has a very different sensitivity than the grounded side (β2). The CMRR is twice the feedback factor difference divided by the feedback fac-tor sum. The differential output offset voltage has two terms. The first term is determined by the input offset term, VOSDIFF, and the application’s gain. Note that this term equates to the formula in Figure 3 when β1 equals β2. The amount of signal level shifting and the feedback factor mismatch determines the second term. This term

Table 1. Input Signal Limitations for Some Common Applications

Single Supply Ground Referenced Single-Ended Input Signal, VOCM at Mid-Supply. (The VINSIG Min and Max values listed account for both the input common mode limits and the output clipping)

Single Supply Ground Referenced Single-Ended Input Signal, VOCM at Typical ADC Reference Levels. (The VINSIG Min and Max values listed account for both the input common mode limits and the output clipping)

+VS(V)

–VS(V)

GAIN(V/V)

VOCM(V)

VINREF(V)

VINSIG(MAX)(V)

VINSIG(MIN)(V)



2.7 0 1 1.35 0 2.700 –2.700 5.40 5.40

2.7 0 2 1.35 0 1.350 –1.350 2.70 5.40

2.7 0 5 1.35 0 0.540 –0.540 1.08 5.40

2.7 0 10 1.35 0 0.270 –0.270 0.54 5.40

5 0 1 2.5 0 5.000 –5.000 10.00 10.00

5 0 2 2.5 0 2.500 –2.500 5.00 10.00

5 0 5 2.5 0 1.000 –1.000 2.00 10.00

5 0 10 2.5 0 0.500 –0.500 1.00 10.00

+VS(V)

–VS(V)

GAIN(V/V)

VOCM(V)

VINREF(V)

VINSIG(MAX)(V)

VINSIG(MIN)(V)



2.7 0 1 1 0 2.000 –2.000 4.00 4.00

2.7 0 2 1 0 1.000 –1.000 2.00 4.00

2.7 0 5 1 0 0.400 –0.400 0.80 4.00

2.7 0 10 1 0 0.200 –0.200 0.40 4.00

5 0 1 2 0 4.000 –4.000 8.00 8.00

5 0 2 2 0 2.000 –2.000 4.00 8.00

5 0 5 2 0 0.800 –0.800 1.60 8.00

5 0 10 2 0 0.400 –0.400 0.80 8.00

LTC1992 Family

361992fb


quantifies the undesired effect of signal level shifting discussed earlier in the Signal Level Shifting section.

Asymmetrical Feedback Application Circuits

The basic signal equation in Figure 6 also gives insight to another piece of intuition. The feedback factors may be deliberately set to different values. One interesting class of these application circuits sets one or both of the feedback factors to the extreme values of either zero or one. Figure 7 shows three such circuits.

At first these application circuits may look to be unstable or open loop. It is the common mode feedback loop that enables these circuits to function. While they are useful circuits, they have some shortcomings that must be con-sidered. First, due to the severe feedback factor asymmetry, the VOCM level influences the differential output voltage with about the same strength as the input signal. With this much gain in the VOCM path, differential output offset and noise increase. The large VOCM to VOUTDIFF gain also necessitates that these circuits are largely limited to dual,

split supply voltage applications with a ground referenced input signal and a grounded VOCM pin.

The top application circuit in Figure 7 yields a high input impedance, precision gain of 2 block without any external resistors. The on-chip common mode feedback servo resistors determine the gain precision (better than 0.1 percent). By using the –VOUT output alone, this circuit is also useful to get a precision, single-ended output, high input impedance inverter. To intuitively understand this circuit, consider it as a standard op amp voltage follower (delivered through the signal gain servo) with a comple-mentary output (delivered through the common mode level servo). As usual, the amplifier’s input common mode range must not be exceeded. As with a standard op amp voltage follower, the common mode signal seen at the amplifier’s input is the input signal itself. This condition limits the input signal swing, as well as the output signal swing, to be the input signal common mode range specification.

The middle circuit is largely the same as the first except that the noninverting amplifier path has gain. Note that

Figure 6. Basic Equations for Mismatched or Asymmetrical Feedback Applications Circuits

–

–+

+RIN2

RIN1

2[+VIN • (1 – 1) – (–VIN) • (1 – 2)] + 2VOSDIFF + 2VOUTCM ( 1 – 2)

1 + 2

RFB1

VOCMVOCM

VOUTDIFF =

WHERE:

• FOR GROUND REFERENCED, SINGLE-ENDED INPUT SIGNAL, LET +VIN = VINSIG AND –VIN = 0V

RFB2

–VIN

VINDIFF+VIN – –VIN

+VIN –VOUT

+VOUT

1992 F06

LTC1992 VOUTDIFF+VOUT – –VOUT

2 • VINSIG • (1 – 1) + 2VOSDIFF + 2VOUTCM ( 1 – 2)

1 + 2VOUTDIFF =

• COMMON MODE REJECTION: SET +VIN = –VIN = VINCM, VOSDIFF = 0V, VOUTCM = 0V

ΔVINCM

ΔVOUTDIFFCMRR = = 2 ; OUTPUT REFERRED

1 + 2

2 – 1

2 – 1

1 + 2

• OUTPUT DC OFFSET VOLTAGE: SET +VIN = –VIN = VINCM

VOSDIFFOUT = VOSDIFF + (VOUTCM – VINCM) 22

1 + 2

RIN1

RIN1 + RFB11 = ; 2 = ; VOSDIFF = AMPLIFIER INPUT REFERRED OFFSET VOLTAGE

VOUTCM = KCM • VOCM + VOSCM

0.999 < KCM < 1.001

RIN2

RIN2 + RFB2

LTC1992 Family

371992fb

Figure 7. Asymmetrical Feedback Application Circuits (Most Suitable in Applications with Dual, Split Supplies (e.g., ±5V), Ground Referenced Single-Ended Input Signals and VOCM Connected to Ground)

once the VOCM voltage is set to zero, the gain formula is the same as a standard noninverting op amp circuit multiplied by two to account for the complementary output. Taking RFB to zero (i.e., taking β to one) gives the same formula as the top circuit. As in the top circuit, this circuit is also useful as a single-ended output, high input impedance inverting gain block (this time with gain). The input com-mon mode considerations are similar to the top circuit’s, but are not nearly as constrained since there is now gain in the noninverting amplifier path. This circuit, with VOCM at ground, also permits a rail-to-rail output swing in most applications.

The bottom circuit is another circuit that utilizes a standard op amp configuration with a complementary output. In this case, the standard op amp circuit has an inverting con-figuration. With VOCM at zero volts, the gain formula is the same as a standard inverting op amp circuit multiplied by two to account for the complementary output. This circuit does not have any common mode level constraints as the inverting input voltage sets the input common mode level. This circuit also delivers rail-to-rail output voltage swing without any concerns.


–

–+

+ +VOUT VOUTDIFF = 2(+VIN – VOCM)

SETTING VOCM = 0V

VOUTDIFF = 2VIN

–VOUTVIN

VOCM VOCM LTC1992

–

–+

+ +VOUT

RFBRIN

VOUTDIFF = 2

SETTING VOCM = 0V

VOUTDIFF = 2VIN

–VOUTVIN

VOCM

RIN

RFB

( )+VIN ; =

= 2VIN 1 +

– VOCM1

( )1 ( )

RIN

RIN + RFB

RFB

RIN

–

–+

+ +VOUT VOUTDIFF = 2

SETTING VOCM = 0V

VOUTDIFF = 2VIN

–VOUT

1992 F07

VIN

VOCM

( )+VIN ; =

= 2VIN

+ VOCM1 –

( )1 – ( )

RIN

RIN + RFB

RFB

RIN

VOCM LTC1992

VOCM LTC1992

LTC1992 Family

381992fb

TYPICAL APPLICATIONS

Interfacing a Bipolar, Ground Referenced, Single-Ended Signal to a Unipolar Single Supply, Differential Input ADC (VIN = 0V Gives a Digital Mid-Scale Code)

Compact, Unipolar Serial Data Conversion

Zero Components, Single-Ended Adder/Subtracter

–

–+

+

LTC1992

3

6

VOCM

VMID

0.1μF

100pF

7

6

5

13.3k

40k

4

5

2

7

8

110k

10k

5V

13.3k

40k

5V

10k

10k

100Ω

100Ω

0.1μF

+INVREF VCC2

1 8

3

4

1992 TA02a

–IN

1μF

SCK

SDO

CONV

LTC1864

SERIALDATALINK

GND0VVIN

2.5V

–2.5V

–

–+

+

LTC1992-2

3

6

VOCM

VMID

0.1μF

100pF

7

6

5

4

5

2

7

8

1 100Ω

5V

100Ω

0.1μF

+INVREF VCC2

1 8

3

4

1992 TA03a

–IN

1μF

SCK

SDO

CONV

LTC1864SERIALDATALINK

GNDVIN

2.5V

0V

–

–+

+ V1 = VB + VC – VA

V2 = VB + VA – VC

VA1 4

0.1μF

3

+VS

–VS

65

2

8VC

VB VOCM LTC1992-2

0.1μF

1992 TA04

LTC1992 Family

391992fb

TYPICAL APPLICATIONS

Single-Ended to Differential Conversion Driving an ADC

2.2μF 10μF 10μF10Ω

47μF

4

6

REFCOMP

4.375V

CONTROLLOGICAND

TIMING

B15 TO B016-BIT

SAMPLINGADC

–

+10μF

5V OR3V

μPCONTROLLINES

D15 TO D0

OUTPUTBUFFERS

16-BITPARALLELBUS

11 TO 26

1992 TA06a

OGND

OVDD

28

29

1

2

AIN+

AIN–

SHDN

CS

CONVST

RD

BUSY

33

32

31

30

27

LTC1603

3 36 35 109

5V 5V

AVDD AVDD

7.5k

DVDD DGNDVREF

8

AGNDAGND

7

AGND

5

AGND

34

–5V

VSS

10μF

2.5VREF

10μF

1.75X+

+ + +

+

+

–

–+

+

5V

–5V

LTC1992-1

3

6

VOCM

VMID

VIN

100pF

4

5

2

7

8

1 100Ω

100Ω

0.1μF

0.1μF

FFT of the Output Data

SNR =85.3dBTHD = –72.1dBSINAD = –72dB

fIN = 10.0099kHzfSAMPLE = 333kHz

0

–10

–20

–30

–40

–50

–60

–70

–80

–90

–100

–110

–120

–130

–140

FREQUENCY (kHz)

0

AM

PLIT

UD

E (

dB

)

8070

1992 TA06b

2010 4030 6050 10090

LTC1992 Family

401992fb

PACKAGE DESCRIPTION

MS8 Package8-Lead Plastic MSOP

(Reference LTC DWG # 05-08-1660 Rev F)

MSOP (MS8) 0307 REV F

0.53 0.152

(.021 .006)

SEATINGPLANE

NOTE:1. DIMENSIONS IN MILLIMETER/(INCH)2. DRAWING NOT TO SCALE3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX

0.18

(.007)

0.254

(.010)

1.10

(.043)MAX

0.22 – 0.38

(.009 – .015)TYP

0.1016 0.0508

(.004 .002)

0.86

(.034)REF

0.65

(.0256)BSC

0 – 6 TYP

DETAIL “A”

DETAIL “A”

GAUGE PLANE

1 2 3 4

4.90 0.152

(.193 .006)

8 7 6 5

3.00 0.102

(.118 .004)

(NOTE 3)

3.00 0.102

(.118 .004)

(NOTE 4)

0.52

(.0205)REF

5.23(.206)MIN

3.20 – 3.45(.126 – .136)

0.889 0.127(.035 .005)

RECOMMENDED SOLDER PAD LAYOUT

0.42 0.038(.0165 .0015)

TYP

0.65(.0256)

BSC

LTC1992 Family

411992fb

Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

REVISION HISTORYREV DATE DESCRIPTION PAGE NUMBER

A 7/10 Updated Part Markings 2

B 6/11 Revised Features

Updated to Specified Temperature Range in Absolute Maximum Ratings and Order Information

Revised Block Diagram

Revised subtitle in Figure 5 of Applications Information section

1

2

24

32

LTC1992 Family

421992fb

Linear Technology Corporation1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2005

LT 0611 REV A • PRINTED IN USA

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TYPICAL APPLICATION

PART NUMBER DESCRIPTION COMMENTS

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LT6600-X Differential In/Out Amplifier Lowpass Filter Very Low Noise, Standard Differential Amplifier Pinout

BNC

VINP

–

–+

+1 4 7

8

11

4

12

17

13

14

16

0.1μF

V+

1/2 LTC1043

3

5V

–5V

65

2

8VOCM

7

BNC

VINP

VOCM

VMIDLTC1992

0.1μF

0.1μF

CLKV–

0.1μF

1992 TA05a

0.1μF

CLK

0.1μF

–

–+

+1 4

3

65

2

8VOCM

7VMID

LTC1992BNC

VOUTM

BNC

VOUTP

60kHz LOW PASS FILTER SAMPLER 2kHz LOWPASS FILTER

9.53k

9.53k

9.53k

37.4k 60.4k

37.4k 60.4k

9.53k 8.87k

8.87k

75k

75k

120pF

120pF

390pF

390pF

330pF

180pF

0.1μF10k

Balanced Frequency Converter (Suitable for Frequencies up to 50kHz)

0V

0V

0V

0V

200μs/DIV

VINP = 24kHz(1V/DIV)

VOUTP = 1kHz(0.5V/DIV)VOUTM = 1kHz(0.5V/DIV)

CLK = 25kHz(LOGIC SQUARE WAVE)(5V/DIV)

1992 TA05b

ltc1992 family - low power, fully differential input ... · the ltc ®1992 product family consists...

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