Design of an Instrumentation Amplifier

Instrumentation Amplifier

Differential Pair with Active LoadBias Voltage Generation

Anatomy of a Different Pair with Active Load

Differential Pair (Sec. 10.3)

Differential Pair with Active Load(Sec. 10.3)

Current Mirror (Section 9.2)

Bias Voltage Generation

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)

Common Source Amplifier Design

Design spec:

1 uA of bias currentAV=-30 V/V of gain.

Measure Peak to Peak Voltage

The gain is approximately 30.

Voltage Gain

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!

Cascode Circuit

Matlab Computation

ro2 is 1.526 Mohmsgmovergds_2=30 Mohms

Rout is 55.2 Mohms

Gain Calculation

We should be increase the gain from 30 to 97.

DC of Vout is too low!

The gate bias voltage for T0=284.4 mV

The gate bias voltageFor T1 is 0.33 V +0.3 V0.63 V

The output voltage doesIs only 71.87 mV What happens?

Calculate the Gain of a Circuit Using Norton Equivalent Circuit

Short Circuit Transconductrance

Sweep DC Voltage

Define DC voltage as a variable.

Copy from Cellview

Setup the Sweep

Run Parametric Analysis

Use Sweep to Zoom on the Correct Gate Bias Voltage

We want to keep the output voltage close to 0.6 V.

Adjust Gate Voltage

Gate voltage of T0:255 mV

Matlab: 284 mVWe were off by 31 mV

Vin and Vout

A faster way to calculate voltage gain is using the calculator.

A gain of 88!

Using the Calculator

Calculate Peak to Peak Voltage