---
title: "Short note: Instrumentation amplifier"
subject: "Advanced Electronics"
chapter: 4
key: "semester_4/advanced_electronics:short-note-instrumentation-amplifier"
source: https://www.bctengineer.com/q/semester_4/advanced_electronics/short-note-instrumentation-amplifier
site: BCT Engineering
---

# Short note: Instrumentation amplifier

Advanced Electronics · Chapter 4: Instrumentation and Isolation Amplifiers

- Asked in: 2070 Asar, 3 marks
- Video: [Instrumentation Amplifiers Explained (Amplifiers #7)](https://www.youtube.com/watch?v=VfJ2AHO2aHg) — Aaron Danner
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/advanced_electronics/short-note-instrumentation-amplifier
- Whole chapter: https://www.bctengineer.com/md/semester_4/advanced_electronics/chapter-4

## Question

Write a short note on instrumentation amplifier.

## Short answer

An instrumentation amplifier is a precision differential amplifier with buffered high-impedance inputs, high CMRR, and gain set by a single resistor. The three-op-amp topology gives Vo = (R3/R2)*(1+2R1/RG)*(V2-V1); common-mode signals are passed with gain 1 then canceled. It is used for transducer signal conditioning such as ECG, strain gauges, and data acquisition.

## Answer

An **instrumentation amplifier (IA)** is a precision differential amplifier with buffered inputs. It amplifies small differential signals (mV or µV) from transducers such as strain gauges, thermocouples and ECG electrodes, while rejecting large common-mode noise.

**Features:**
- Very high input impedance, so it does not load the source
- High CMRR (100 dB or more)
- Gain set accurately by one resistor RG, typically 1 to 1000
- Low offset, drift and noise; low output impedance

**Three op-amp IA:**
```text
 V1->(+)A1-Vo1-[R2]-+-[R3]-+
       |R1         (-)A3---+-> Vo
       RG          (+)
       |R1          |
 V2->(+)A2-Vo2-[R2]-+-[R3]-GND
```

A1 and A2 are input buffers with gain. A3 is a difference amplifier.

```text
Vo = (R3/R2)(1 + 2R1/RG)(V2 − V1)
```

A common-mode input causes no current in RG, so it passes the first stage with gain 1 and is cancelled by A3.

**Applications:** bridge and strain-gauge amplifiers, temperature measurement, medical instruments (ECG, EEG), and data acquisition. Example ICs: AD620, INA128.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What does an IA do?
   A. Amplify small differential transducer signals while rejecting large common-mode noise
   B. Amplify noise
   C. Convert AC to DC
   D. Generate clock
   Answer: A. That is the defining use of an IA. (Key point: Purpose)

2. How is the IA gain set?
   A. By one resistor RG
   B. By the supply voltage
   C. By four matched resistors
   D. By the input source
   Answer: A. Vo = (R3/R2)(1 + 2R1/RG)(V2 - V1), varied through RG. (Key point: Gain setting)

3. A common-mode input in the 3 op-amp IA is:
   A. Passed with gain 1 in stage one and cancelled by A3
   B. Amplified 1000 times
   C. Blocked by RG
   D. Converted to a differential signal
   Answer: A. No current flows in RG, and A3 subtracts. (Key point: Common-mode handling)

## Related in Advanced Electronics

- [Design three op-amp IA with gain 20](https://www.bctengineer.com/question.md?key=semester_4%2Fadvanced_electronics%3Adesign-3opamp-ia-gain-20) — Advanced Electronics, chapter 4, asked 3×
- [Design three op-amp IA with gain 50](https://www.bctengineer.com/question.md?key=semester_4%2Fadvanced_electronics%3Adesign-3opamp-ia-gain-50) — Advanced Electronics, chapter 4, asked 3×
- [IA features; 3 op-amp IA output voltage](https://www.bctengineer.com/question.md?key=semester_4%2Fadvanced_electronics%3Aia-features-3opamp-output) — Advanced Electronics, chapter 4
- [Output voltage of two op-amp IA](https://www.bctengineer.com/question.md?key=semester_4%2Fadvanced_electronics%3Atwo-opamp-ia-output) — Advanced Electronics, chapter 4
- [Single op-amp IA with mismatched resistances](https://www.bctengineer.com/question.md?key=semester_4%2Fadvanced_electronics%3Asingle-opamp-ia-mismatched) — Advanced Electronics, chapter 4
- [Ideal IA characteristics; optically coupled isolation](https://www.bctengineer.com/question.md?key=semester_4%2Fadvanced_electronics%3Aia-ideal-optical-isolation) — Advanced Electronics, chapter 4

## Related in other subjects

- [Instrumentation amplifier and its gain](https://www.bctengineer.com/question.md?key=semester_4%2Finstrumentation_i%3Ainstrumentation-amplifier-gain) — Instrumentation I, chapter 4
- [Piezoelectric load cell and charge amplifier](https://www.bctengineer.com/question.md?key=semester_4%2Finstrumentation_and_measurement%3Apiezoelectric-load-cell-charge-numerical) — Instrumentation and Measurement, chapter 7