---
title: "Short note: CMRR, PSRR and slew rate"
subject: "Advanced Electronics"
chapter: 2
key: "semester_4/advanced_electronics:define-cmrr-psrr-slew-rate"
source: https://www.bctengineer.com/q/semester_4/advanced_electronics/define-cmrr-psrr-slew-rate
site: BCT Engineering
---

# Short note: CMRR, PSRR and slew rate

Advanced Electronics · Chapter 2: Operational Amplifier Characterization

- Asked in: 2072 Kartik, 3 marks
- Video: [PARAMETERS OF OP-AMP | offset voltage, CMRR in op-amp, SVRR in op-amp, slew rate, thermal drift](https://www.youtube.com/watch?v=i_z6ikX80fk) — Electronics Subjectified
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/advanced_electronics/define-cmrr-psrr-slew-rate
- Whole chapter: https://www.bctengineer.com/md/semester_4/advanced_electronics/chapter-2

## Question

Define the terms CMRR, PMRR (PSRR) and Slew Rate.

## Short answer

CMRR is the ratio of differential gain to common-mode gain, expressed in dB. PSRR is the change in input offset voltage per unit supply voltage change (µV/V); smaller is better. Slew rate is the maximum rate of change of output voltage, dVo/dt in V/µs.

## Answer

- **CMRR (common-mode rejection ratio):** the ratio of differential gain to common-mode gain, CMRR = |Ad/Acm|, usually in dB: CMRR = 20 log10|Ad/Acm|. It shows how well the op-amp rejects signals (noise, hum) common to both inputs. For the 741 it is about 90 dB; ideal is infinite.
- **PSRR (power supply rejection ratio, also SVRR):** the change in input offset voltage per unit change in one supply voltage, the other supply being constant: PSRR = ΔVio/ΔV, in µV/V (or dB). It shows how well the op-amp rejects supply ripple and variation. For the 741 it is 30 µV/V typical; smaller is better.
- **Slew rate (SR):** the maximum rate of change of output voltage, SR = (dVo/dt)max, in V/µs. It is set by the current charging the internal compensation capacitor (SR = Imax/C). For the 741 it is 0.5 V/µs. A sine output of peak Vm is undistorted only up to fmax = SR/(2πVm).

## Check yourself

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

1. What does CMRR of an op-amp measure?
   A. Ratio of differential gain to common-mode gain
   B. Ratio of common-mode gain to differential gain
   C. Change in offset voltage per unit supply change
   D. Maximum rate of change of output voltage
   Answer: A. CMRR = |Ad/Acm|; a high value means common-mode signals such as hum are rejected well. (Key point: CMRR definition)

2. PSRR (SVRR) of an op-amp is defined as:
   A. Change in output voltage per unit change in input current
   B. Change in input offset voltage per unit change in one supply voltage
   C. Ratio of differential gain to common-mode gain
   D. Output change per unit time
   Answer: B. PSRR = ΔVio/ΔV in µV/V, with the other supply held constant; smaller is better. (Key point: PSRR definition)

3. What sets the slew rate of an op-amp?
   A. The open-loop gain at DC
   B. The input offset voltage
   C. Maximum current available to charge the internal compensation capacitor (SR = Imax/C)
   D. The common-mode gain
   Answer: C. SR = Imax/C, so a larger charging current or smaller capacitor gives a higher slew rate. (Key point: Slew rate cause)

4. A sine output of peak Vm is undistorted only up to which frequency?
   A. fmax = SR x 2πVm
   B. fmax = 2πVm/SR
   C. fmax = SR/Vm
   D. fmax = SR/(2πVm)
   Answer: D. The maximum slope of Vm sin(2πft) is 2πfVm, which must not exceed SR. (Key point: Slew-rate limit on sine)

## Related in Advanced Electronics

- [Slew-rate distortion check, 470 kΩ/10 kΩ inverter](https://www.bctengineer.com/question.md?key=semester_4%2Fadvanced_electronics%3Aslew-rate-470k-10k) — Advanced Electronics, chapter 2, asked 3×
- [Slew-rate check for 40 dB amplifier at 20 kHz](https://www.bctengineer.com/question.md?key=semester_4%2Fadvanced_electronics%3Aslew-rate-40db-20khz) — Advanced Electronics, chapter 2
- [Slew rate expressions and constant GBP](https://www.bctengineer.com/question.md?key=semester_4%2Fadvanced_electronics%3Aslew-rate-gbp-constant) — Advanced Electronics, chapter 2
- [Slew-rate check for four input signals](https://www.bctengineer.com/question.md?key=semester_4%2Fadvanced_electronics%3Aslew-rate-multiple-signals) — Advanced Electronics, chapter 2
- [Slew-rate distortion check, 330 kΩ/10 kΩ inverter](https://www.bctengineer.com/question.md?key=semester_4%2Fadvanced_electronics%3Aslew-rate-330k-10k) — Advanced Electronics, chapter 2
- [Voltage follower square-wave output with slew rate](https://www.bctengineer.com/question.md?key=semester_4%2Fadvanced_electronics%3Avoltage-follower-square-wave) — Advanced Electronics, chapter 2