digital to analog converters (dac)
DESCRIPTION
Digital to Analog Converters (DAC). Adam Fleming Mark Hunkele 3/11/2005. Outline. Purpose Types Performance Characteristics Applications. Reference Voltage. DAC. Digital Value. Analog Voltage. Purpose. To convert digital values to analog voltages - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/1.jpg)
Digital to Analog Converters (DAC)
Adam FlemingMark Hunkele
3/11/2005
![Page 2: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/2.jpg)
2
Outline
Purpose Types Performance Characteristics Applications
![Page 3: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/3.jpg)
3
Purpose
To convert digital values to analog voltages Performs inverse operation of the Analog-to-
Digital Converter (ADC)
DACDigital Value Analog Voltage
Reference Voltage
Value DigitalOUTV
![Page 4: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/4.jpg)
4
DACs
Types Binary Weighted Resistor R-2R Ladder Multiplier DAC
The reference voltage is constant and is set by the manufacturer. Non-Multiplier DAC
The reference voltage can be changed during operation. Characteristics
Comprised of switches, op-amps, and resistors Provides resistance inversely proportion to
significance of bit
![Page 5: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/5.jpg)
5
Binary Weighted ResistorRf = R
8R4R2RR Vo
-VREF
iI
LSB
MSB
![Page 6: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/6.jpg)
6
Binary RepresentationRf = R
8R4R2RR Vo
-VREF
iI
Least Significant Bit
Most Significant Bit
![Page 7: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/7.jpg)
7
Binary Representation
-VREF
Least Significant Bit
Most Significant Bit
CLEAREDSET
( 1 1 1 1 )2 = ( 15 )10
![Page 8: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/8.jpg)
8
Binary Weighted Resistor
Rf = R
8R4R2RR Vo
-VREF
iI
LSB
MSB
“Weighted Resistors” based on bit
Reduces current by a factor of 2 for each bit
![Page 9: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/9.jpg)
9
Binary Weighted Resistor
Result:
Bi = Value of Bit i
R
B
R
B
R
B
R
BVI REF 842
0123
842012
3
BBBBVRIV REFfOUT
![Page 10: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/10.jpg)
10
Binary Weighted Resistor
More Generally:
Bi = Value of Bit i
n = Number of Bits
ResolutionValue Digital2 1
REF
ini
REFOUT
V
BVV
![Page 11: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/11.jpg)
11
R-2R LadderVREF
MSB
LSB
![Page 12: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/12.jpg)
12
R-2R Ladder
Same input switch setup as Binary Weighted Resistor DAC
All bits pass through resistance of 2R
VREFMSB
LSB
![Page 13: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/13.jpg)
13
R-2R Ladder
The less significant the bit, the more resistors the signal muss pass through before reaching the op-amp
The current is divided by a factor of 2 at each node
LSB MSB
![Page 14: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/14.jpg)
14
R-2R Ladder The current is divided by a factor of 2 at each node Analysis for current from (001)2 shown below
0I
VREF
RR R R 2R
2R2R2R
Op-Amp input“Ground”
B0
20I
40I
80I
R
V
RRR
VI REFREF
32220
B1B2
![Page 15: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/15.jpg)
15
R-2R Ladder
Result:
Bi = Value of Bit i
842012 BBB
VR
RV REF
fOUT
Rf
8423012 BBB
R
VI REF
![Page 16: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/16.jpg)
16
R-2R Ladder
If Rf = 6R, VOUT is same as Binary Weighted:
Bi = Value of Bit i
12 in
iREFOUT
BVV
in
iREF B
R
VI
23
![Page 17: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/17.jpg)
17
0I
VREF
RR R R 2R
2R2R2R
Op-Amp input“Ground”
B0B2
0I
VREF
R-2R Ladder Example:
Input = (101)2
VREF = 10 V R = 2 Ω Rf = 2R
mA67.132220
R
V
RRR
VI REFREF
mA04.12800
III ampop
V17.4 fampopOUT RIV
![Page 18: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/18.jpg)
18
Pros & Cons
Binary Weighted R-2R
Pros Easily understood
Only 2 resistor values
Easier implementation
Easier to manufacture
Faster response time
Cons
Limited to ~ 8 bits
Large # of resistors
Susceptible to noise
Expensive
Greater Error
More confusing analysis
![Page 19: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/19.jpg)
19
Digital to Analog ConvertersDigital to Analog Converters
Performance Specifications
Common Applications
Presented by: Mark Hunkele
![Page 20: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/20.jpg)
20
Digital to Analog Converters
-Performance SpecificationsPerformance Specifications
Resolution Reference Voltages Settling Time Linearity Speed Errors
![Page 21: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/21.jpg)
21
Resolution: is the amount of variance in output voltage for every change of the LSB in the digital input.
How closely can we approximate the desired output signal(Higher Res. = finer detail=smaller Voltage divisions)
A common DAC has a 8 - 12 bit Resolution
Digital to Analog Converters
-Performance Specifications
--ResolutionResolution
NLSB
VV
2Resolution Ref N = Number of bits
![Page 22: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/22.jpg)
22
Digital to Analog Converters
-Performance Specifications
-Resolution-Resolution
Better Resolution(3 bit)Poor Resolution(1 bit)
Vout
Desired Analog signal
Approximate output
2 V
olt.
Lev
els
Digital Input0 0
1
Digital Input
Vout
Desired Analog signal
Approximate output
8 V
olt.
Lev
els
000
001
010
011
100
101
110
111
110
101
100
011
010
001
000
![Page 23: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/23.jpg)
23
Reference Voltage: A specified voltage used to determine how each digital input will be assigned to each voltage division.
Types:Non-multiplier: internal, fixed, and defined by
manufacturerMultiplier: external, variable, user specified
Digital to Analog Converters
-Performance Specifications
-Reference VoltageReference Voltage
![Page 24: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/24.jpg)
24
Digital to Analog Converters
-Performance Specifications
-Reference VoltageReference Voltage
Assume 2 bit DAC
Non-Multiplier: (Vref = C)
Digital Input
Multiplier: (Vref = Asin(wt))
0
Voltage
00
01 01
00
10 10
11
0
Voltage
Digital Input00 00
01 01
10 10
11
![Page 25: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/25.jpg)
25
Settling Time: The time required for the input signal voltage to settle to the expected output voltage(within +/- VLSB).
Any change in the input state will not be reflected in the output state immediately. There is a time lag, between the two events.
Digital to Analog Converters
-Performance Specifications
-Settling Time-Settling Time
![Page 26: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/26.jpg)
26
Digital to Analog Converters
-Performance Specifications
-Settling Time-Settling Time
Analog Output Voltage
Expected Voltage
+VLSB
-VLSB
Settling timeTime
![Page 27: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/27.jpg)
27
Linearity: is the difference between the desired analog output and the actual output over the full range of expected values.
Ideally, a DAC should produce a linear relationship between a digital input and the analog output, this is not always the case.
Digital to Analog Converters
-Performance Specifications
-Linearity-Linearity
![Page 28: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/28.jpg)
28
Digital to Analog Converters
-Performance Specifications
-Linearity-Linearity
Linearity(Ideal Case)
Digital Input
Perfect Agreement
Desired/Approximate Output
Ana
log
Out
put V
olta
ge
NON-Linearity(Real World)
Ana
log
Out
put V
olta
ge
Digital Input
Desired Output
Miss-alignment
Approximate output
![Page 29: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/29.jpg)
29
Speed: Rate of conversion of a single digital input to its analog equivalent
Conversion Rate Depends on clock speed of input signalDepends on settling time of converter
Digital to Analog Converters
-Performance Specifications
-SpeedSpeed
![Page 30: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/30.jpg)
30
Non-linearityDifferential Integral
Gain Offset Non-monotonicity
Digital to Analog Converters
-Performance Specifications
-Errors-Errors
![Page 31: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/31.jpg)
31
Differential Non-Linearity: Difference in voltage step size from the previous DAC output (Ideally All DLN’s = 1 VLSB)
Digital to Analog Converters
-Performance Specifications
-Errors: Differential Non-Linearity-Errors: Differential Non-Linearity
Digital Input
Ideal Output
Ana
log
Out
put V
olta
ge
VLSB
2VLSB Diff. Non-Linearity = 2VLSB
![Page 32: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/32.jpg)
32
Integral Non-Linearity: Deviation of the actual DAC output from the ideal (Ideally all INL’s = 0)
Digital to Analog Converters
-Performance Specifications
-Errors: Integral Non-Linearity-Errors: Integral Non-Linearity
Digital Input
Ideal Output
1VLSB Int. Non-Linearity = 1VLSB
Ana
log
Out
put V
olta
ge
![Page 33: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/33.jpg)
33
Gain Error: Difference in slope of the ideal curve and the actual DAC output
Digital to Analog Converters
-Performance Specifications
-Errors: Gain-Errors: Gain
High Gain Error: Actual slope greater than ideal
Low Gain Error: Actual slope less than ideal
Digital Input
Desired/Ideal OutputA
nalo
g O
utpu
t Vol
tage
Low Gain
High Gain
![Page 34: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/34.jpg)
34
Offset Error: A constant voltage difference between the ideal DAC output and the actual. The voltage axis intercept of the DAC output curve is
different than the ideal.
Digital to Analog Converters
-Performance Specifications
-Errors: Offset-Errors: Offset
Digital Input
Desired/Ideal OutputOutput Voltage
Positive Offset
Negative Offset
![Page 35: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/35.jpg)
35
Non-Monotonic: A decrease in output voltage with an increase in the digital input
Digital to Analog Converters
-Performance Specifications
-Errors: Non-Monotonicity-Errors: Non-Monotonicity
Ana
log
Out
put V
olta
ge
Digital Input
Desired Output
Monotonic
Non-Monotonic
![Page 36: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/36.jpg)
36
Generic use Circuit Components Digital Audio Function Generators/Oscilloscopes Motor Controllers
Digital to Analog Converters
-Common ApplicationsCommon Applications
![Page 37: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/37.jpg)
37
Used when a continuous analog signal is required.
Signal from DAC can be smoothed by a Low pass filter
Digital to Analog Converters
-Common Applications
-Generic-Generic
0 bit
nth bit
n bit DAC011010010101010100101101010101011111100101000010101010111110011010101010101010101010111010101011110011000100101010101010001111
Digital Input
Filter
Piece-wise Continuous Output
Analog Continuous Output
![Page 38: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/38.jpg)
38
Voltage controlled Amplifier digital input, External Reference Voltage as control
Digitally operated attenuator External Reference Voltage as input, digital control
Programmable Filters Digitally controlled cutoff frequencies
Digital to Analog Converters
-Common Applications
-Circuit Components-Circuit Components
![Page 39: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/39.jpg)
39
CD Players MP3 Players Digital Telephone/Answering Machines
Digital to Analog Converters
-Common Applications
-Digital Audio-Digital Audio
1. http://electronics.howstuffworks.com/cd.htm2. http://accessories.us.dell.com/sna/sna.aspx?c=us&cs=19&l=en&s=dhs&~topic=odg_dj
1 2 3
3. http://www.toshiba.com/taistsd/pages/prd_dtc_digphones.html
![Page 40: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/40.jpg)
40
Digital to Analog Converters
-Common Applications
-Function Generators-Function Generators
Digital Oscilloscopes Digital Input Analog Ouput
Signal Generators Sine wave generation Square wave generation Triangle wave generation Random noise generation
1
1. http://www.electrorent.com/products/search/General_Purpose_Oscilloscopes.html
2
2. http://www.bkprecision.com/power_supplies_supply_generators.htm
![Page 41: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/41.jpg)
41
Cruise Control Valve Control Motor Control
Digital to Analog Converters
-Common Applications
-Motor Controllers-Motor Controllers
1
1. http://auto.howstuffworks.com/cruise-control.htm
2
2. http://www.emersonprocess.com/fisher/products/fieldvue/dvc/
3
3. http://www.thermionics.com/smc.htm
![Page 42: Digital to Analog Converters (DAC)](https://reader036.vdocuments.site/reader036/viewer/2022082207/568152ce550346895dc0e817/html5/thumbnails/42.jpg)
42
References
Cogdell, J.R. Foundations of Electrical Engineering. 2nd ed. Upper Saddle River, NJ: Prentice Hall, 1996.
“Simplified DAC/ADC Lecture Notes,” http://www-personal.engin.umd.umich.edu/ ~fmeral/ELECTRONICS II/ElectronicII.html
“Digital-Analog Conversion,” http://www.allaboutcircuits.com. Barton, Kim, and Neel. “Digital to Analog Converters.” Lecture, March 21, 2001.
http://www.me.gatech.edu/charles.ume/me4447Spring01/ClassNotes/dac.ppt.
Chacko, Deliou, Holst, “ME6465 DAC Lecture” Lecture, 10/ 23/2003, http://www.me.gatech.edu/mechatronics_course/
Lee, Jeelani, Beckwith, “Digital to Analog Converter” Lecture, Spring 2004, http://www.me.gatech.edu/mechatronics_course/