1
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
2
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
5
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
6
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
7
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
8
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
11
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