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Analog Design Contest - Texas Instruments - 13/11/2012

Wide Bandwidth 90 Degrees Phase Shifter for Lock-in

Amplifiers

DIPARTIMENTO DI ELETTRONICA

E INFORMAZIONE

Marco Vergani – Davide Bianchi Advising Professor: Giorgio Ferrari

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Analog Design Contest - Texas Instruments - 13/11/2012

90° Phase shifter for lock-in Amplifiers

IMPEDANCE MEASUREMENTS

Typical architecture: local oscillator required 90° shifter

x

x

)cos(2

A

)sin(2

A

)cos(2

tA

)cos( t

90° shifter

REFERENCE

INPUT SIGNAL

DC OUTPUT

From Hz to MHz

frequency span

BIO-APPLICATIONS MATERIAL SCIENCE OPTICS

3

Analog Design Contest - Texas Instruments - 13/11/2012

Negative feedback loop

Signal

processing

-

+ VGA

Vg

VOUT

VIN

90° Phase Shifter Concept

Single-pole filter

AIN

Variable Gain Amplifier Amplitude Recovering

Precise 90° delay

AIN -

+ VGA

VOUT

VIN

4

Analog Design Contest - Texas Instruments - 13/11/2012

90°

Single pole

circuit

Phase shift

Vin

VGA

+ -

Rint

Vg

Vout

Rint

Cint

Negative

peak

extraction

Positive

peak

extraction

90° Phase Shifter Concept

Specifications

• 90° shift

• Output amplitude independent to frequency

Proposed Solution

• Precise 90° delay through single pole network

• Input and output amplitude matching through a Variable Gain Amplifier and a DC negative feedback

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Analog Design Contest - Texas Instruments - 13/11/2012

Quasi-peak detector configuration

Asynchronous peak sampling and discharge ripple on Vg

VGA Harmonic distortion increasing at low frequency

+

-

Rint

Vg

Rint Cint

Vin

Vout

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Analog Design Contest - Texas Instruments - 13/11/2012

Synchronous peak comparison

Synchronous discharge NO RIPPLE TO BE FILTERED

NO RIPPLE

at any frequency

Asynchronous peak sampling

+

-

Vg

Rint Cint

Vin

Vout

Rint

Vg+

-

Rint

Rint Cint

Vin

Vout

Rint

+

-

Rint

Vg

Rint Cint

Vin

Vout

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Analog Design Contest - Texas Instruments - 13/11/2012

+

-

+

-

+

-

Vin

Vout

φ1

φ2

φ3R

R

R R+5V

CV

CV V

in

Time

Vout

CloseClose

CloseClose

CloseClose

Open

OpenOpen

Open

OpenOpen

1

Open

2

3

CV

CV

CV

CV

90° Phase Shifter architecture

OPA4354 Wide bandwith CMOS OTA amplifiers TLC3704 Logic ±5V push-pull linear comparators LMH6503 Linear VGA amplifier

3 ICs

90°

Phase

shift

Vin

VGA

x1 x1

+ -

CS1 CS2

φ1 φ2

φ3 φ3

Rint

Vg

Vout

Rint

SW1SW2

SW3

SW4

Cint

VA VB

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Analog Design Contest - Texas Instruments - 13/11/2012

Experimental Results & Outlook

• Phase Error < ±3° • Amplitude precision limited by mismatched

charge injection of the discrete MOSFETs switches.

4 decades frequency span: 30Hz -300kHz

Leakage from the switches Switches speed

Designing of a complete IC

embedded lock-in 90° shifter

x

x

Reference

Input

DC Real

OUTDC Imaginary

OUT

9

Analog Design Contest - Texas Instruments - 13/11/2012

Thank you for the attention

10

Analog Design Contest - Texas Instruments - 13/11/2012

Amplitude error

+

-

Rint

Vg

Rint Cint

Vin

Vout

VA

VB

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Analog Design Contest - Texas Instruments - 13/11/2012

Digital signal generation

• Required to control the switches (discrete MOSFETs) • No external clock required: synchronous with the input signal

+

-

+

-

+

-

Vin

Vout

φ1

φ2

φ3R

R

R R+5V

• Squared input sinusoids • Logic elaboration

Vin

Time

Vout

CloseClose

CloseClose

CloseClose

Open

OpenOpen

Open

OpenOpen

1

Open

2

3

Vin

Time

Vout

CloseClose

CloseClose

CloseClose

Open

OpenOpen

Open

OpenOpen

1

Open

2

3

Vin

Time

Vout

CloseClose

CloseClose

CloseClose

Open

OpenOpen

Open

OpenOpen

1

Open

2

3