TL072 Square Wave Generator

An operational amplifier (op-amp) is a type of electronic amplifier that is commonly used in analog circuits to amplify signals. It is a high-gain, differential voltage amplifier that typically has two input terminals (inverting and non-inverting) and a single output terminal. The op-amp can be configured in various ways to perform different types of operations, such as amplification like audio amplifier, filtering, and signal conditioning. Here it is shown how to build square wave generator using TL072 op-amp.

What is TL072?

The TL072 is a JFET input low-noise, high-speed operational amplifier (op-amp) that is widely used in audio and precision signal processing applications. It has a wide input voltage range and high gain, making it suitable for use in a variety of circuits. The TL072 op-amp is designed to operate from a single power supply, which simplifies the power supply design and reduces the number of components required in a circuit. It also has low offset voltage, low input bias current, and low noise, making it ideal for use in high-precision circuits. The TL072 is available in an 8-pin dual-in-line package (DIP) and is widely available from electronics suppliers. It is a versatile and widely used op-amp that has a well-established reputation for performance and reliability.

 The TLO72 op-amp pinout diagram is shown below.

TLO72 op-amp pinout

Square Wave Generator using Op-Amp

 Op-Amp among other application can be used to generate square wave signal. Square wave signal are used in digital electronics, clocking circuit etc. The following shows circuit diagram of a square wave generator using TL072 Op-Amp.

TL072 square wave generator

A square wave generator can basically designed by configuring an op-amp like TL072 or any other op-amp like LM358, LM471 etc in inverting configuration with the input at the inverting terminal replaced by a capacitor. The resulting circuit is thus a positive feedback circuit with R1 and R2 and a time dependent circuit formed by the resistor R3 and capacitor C2. Thus the feedback voltage which is determined by the resistor R1 and R2. In the above circuit, the TL072 op-amp is configured with single supply voltage of +5V and thus for mid-way voltage at the output, biasing resistors R4 and R5 along with bypass capacitor C1 is used. That is the DC voltage at the non-inverting input is set to 2.5V. The square wave generator circuit is actually a astable multivibrator circuit. To learn the theory behind the op-amp square wave generator or astable multivibrator circuit in general see Astable Multivibrator with Operational Amplifier.

The square wave frequency of oscillation for op-amp square wave circuit is given by the following equation.

\( f_o = \frac{1}{2R_F C ln(\frac{-V_{sat}-V_{LT}}{+V_{sat}-V_{LT}})} \)  ---->(1)
\( V_{UT}=\frac{R_1 V_{sat}}{R_1+R_2} \)   ------->(2)
\( V_{LT}=\frac{-R_1 V_{sat}}{R_1+R_2} \)  ----------->(3)

Using online Op-Amp Astable Multivibrator Calculator we can immediately calculate the required feedback resistor value R3 for the desired frequency of the square wave. So for example, if we want 2kHz square wave, if we take capacitor C2=0.1uF, R1=R2=10kOhm then the value of R3 is 2.28kOhm. We can then choose a standard value for R3=2.2kOhm. Also due to mismatch from different sources, like component tolerance and accuracy, parasitic capacitance either on breadboard or PCB we can use a potentiometer for R1 and R2 to set the required feedback voltage. 


[1] op amp oscillator

[2] colpitts oscillator using op amp

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