Design of an Instrumentation Amplifier

1
Design of an Instrumentation Amplifier
2
Instrumentation Amplifier
Bias Voltage Generation
Differential Pair with Active Load
3
Anatomy of a Different Pair with Active Load
Differential Pair with Active Load (Sec. 10.3)
Differential Pair (Sec. 10.3)
Current Mirror (Section 9.2)
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Bias Voltage Generation
5
Schedule

• Cascode (Section 9.1, 11/14)
• Current Mirror (Section 9.2.3, 11/19)
• Bias Circuitry (Handout, 11/26)
• Differential Pair (Section 10.3, 11/28)
• Differential Pair with Active Load (Section 10.6,
  12/3)
• Instrumentation Amplifier (12/5)

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Common Source Amplifier Design
Design spec 1 uA of bias current AV-30 V/V of
gain.
7
Measure Peak to Peak Voltage
The gain is approximately 30.
8
Voltage Gain
9
Design Exploration

• Initial results
• ro12.228 Mohms
• ro25.32 Mohms
• Av-31.4 V/V
• gmovergds144.57
• gmvoergds242.5

Design If we can increase ro1, we can
potentially raise the gain!
10
Cascode Circuit
11
Matlab Computation
ro2 is 1.526 Mohms gmovergds_230 Mohms Rout is
55.2 Mohms
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Gain Calculation
We should be increase the gain from 30 to 97.
13
DC of Vout is too low!
The gate bias voltage for T0284.4 mV The gate
bias voltage For T1 is 0.33 V 0.3 V 0.63 V
The output voltage does Is only 71.87 mV What
happens?
14
Calculate the Gain of a Circuit Using Norton
Equivalent Circuit
15
Short Circuit Transconductrance
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Sweep DC Voltage
Copy from Cellview
Define DC voltage as a variable.
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Setup the Sweep
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Run Parametric Analysis
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Use Sweep to Zoom on the Correct Gate Bias Voltage
We want to keep the output voltage close to 0.6 V.
20
Adjust Gate Voltage
Gate voltage of T0 255 mV Matlab 284 mV We
were off by 31 mV
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Vin and Vout
A gain of 88!
A faster way to calculate voltage gain is using
the calculator.
22
Using the Calculator
23
Calculate Peak to Peak Voltage