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Design of an Instrumentation Amplifier

Explore the intricacies of designing an instrumentation amplifier, optimizing the bias voltage generation, and increasing the gain through active load and cascode circuits. Gain insight into differential pairs and current mirrors for enhanced performance. Utilize MATLAB for computations and analyze circuit performance using Norton equivalents and transconductance sweeps to achieve desired output voltages. Master the art of voltage gain calculation and peak-to-peak voltage measurements.

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Design of an Instrumentation Amplifier

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  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)

  4. 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)

  6. 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 • ro1=2.228 Mohms • ro2=5.32 Mohms • Av=-31.4 V/V • gmovergds1=44.57 • gmvoergds2=42.5 Design: If we can increase ro1, we can potentially raise the gain!

  10. Cascode Circuit

  11. Matlab Computation ro2 is 1.526 Mohms gmovergds_2=30 Mohms Rout is 55.2 Mohms

  12. Gain Calculation We should be increase the gain from 30 to 97.

  13. DC of Vout is too low! The gate bias voltage for T0=284.4 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

  16. Sweep DC Voltage Copy from Cellview Define DC voltage as a variable.

  17. Setup the Sweep

  18. Run Parametric Analysis

  19. 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

  21. 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

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