---
title: "Square wave generator circuit"
subject: "Electronics Devices and Circuit"
chapter: 5
key: "semester_3/electronics_devices_and_circuit:square-wave-generator-circuit"
source: https://www.bctengineer.com/q/semester_3/electronics_devices_and_circuit/square-wave-generator-circuit
site: BCT Engineering
---

# Square wave generator circuit

Electronics Devices and Circuit · Chapter 5: Signal Generator and Waveform-Shaping Circuits

- Asked in: 2069 Chaitra, 2 marks
- Video: [OP-AMP as Square wave generator](https://www.youtube.com/watch?v=Wh1jU3alWMk) — WIT Solapur - Professional Learning Community
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/electronics_devices_and_circuit/square-wave-generator-circuit
- Whole chapter: https://www.bctengineer.com/md/semester_3/electronics_devices_and_circuit/chapter-5

## Question

Draw the circuit diagram of square wave generator.

## Short answer

An op-amp astable circuit with an RC timing network and positive feedback resistor divider produces a square wave; frequency f = 1/(2RC ln[(1+β)/(1-β)]). Alternatively, a 555 timer astable gives f = 1.44/[(RA+2RB)C].

## Answer

An op-amp astable multivibrator (relaxation oscillator) is a common square-wave generator.

```text
            +--------[ R ]--------+
            |                     |
            |       |\            |
            +-------|-\           |
            |       |  >----+-----+---o Vo (±Vsat)
          [C]   +---|+/     |
            |   |   |/      |
           GND  +--+--[R2]---+
                   |
                 [R1]
                   |
                  GND
```

- R and C form the timing network (R from the output to the inverting input, C to ground).
- R1 and R2 give positive feedback β = R1/(R1 + R2) to the non-inverting input.
- The output swings between +Vsat and −Vsat. The capacitor charges between ±βVsat.

Frequency: f = 1 / {2RC ln[(1 + β)/(1 − β)]}. With R1 = R2 (β = 0.5), f = 1/(2.2 RC).

Another form is the 555 timer astable circuit (RA, RB, C), which gives f = 1.44/((RA + 2RB)C).

## Check yourself

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

1. Which components form the timing network of the op-amp square wave generator?
   A. R from output to inverting input and C to ground
   B. R1 and R2
   C. Rf and R1
   D. Zener and R
   Answer: A. R and C set how fast the capacitor charges between thresholds. (Key point: Timing network)

2. What do R1 and R2 provide?
   A. Positive feedback β = R1/(R1 + R2) to the non-inverting input
   B. Negative feedback to the inverting input
   C. Biasing of the output
   D. Filtering
   Answer: A. They set the switching thresholds ±βVsat. (Key point: Positive feedback)

3. What is f when R1 = R2 (β = 0.5)?
   A. 1/(2.2 RC)
   B. 1/(RC)
   C. 1.44/RC
   D. 1/(2πRC)
   Answer: A. T = 2RC ln3 = 2.2 RC. (Key point: Frequency for R1 = R2)

## Related in Electronics Devices and Circuit

- [Astable multivibrator for square wave generation](https://www.bctengineer.com/question.md?key=semester_3%2Felectronics_devices_and_circuit%3Aastable-multivibrator-square-wave) — Electronics Devices and Circuit, chapter 5
- [Precision half wave rectifier](https://www.bctengineer.com/question.md?key=semester_3%2Felectronics_devices_and_circuit%3Aprecision-half-wave-rectifier) — Electronics Devices and Circuit, chapter 5, asked 5×
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