# Sign Changer Circuit with Op-Amp

Op-amps or operational amplifiers are widely used in electronic circuits for a variety of applications. One such application is the Sign Changer Circuit or phase shifter circuit, which is used to vary the gain of a signal from 1 to -1 and thus change the amplitude and phase of the input signal. In this blog post, we will discuss the working of the Sign Changer Circuit with Op-Amp.

The working of the op-amp based sign changer circuit is shown in the animation below.

What is an op-amp sign changer circuit?

A op-amp based sign changer circuit is a circuit that changes the gain from 1 to -1 of an input signal. Following shows the circuit diagram of op-amp based sign changer.

Working of Sign Changer Circuit with Op-Amp

The Sign Changer Circuit with Op-Amp uses the inverting amplifier configuration of the Op-Amp to change the sign(phase) and amplitude of the input signal. When the wiper of the potentiometer is at the extreme left then the output signal is same as input signal with no change in amplitude and phase. This is because due to this wiper position, the input signal is fed into both the inverting and non-inverting terminal of the op-amp. Therefore amplification of signal from both the terminal happens and the overall gain is given by the following equation.

$$A_v = A_v(invert) +A_v(non-invert)$$   -------->(1)

The voltage gain due to inverting channel is,

$$A_v(invert) = -\frac{R_2}{R_1}$$

$$A_v(invert) = -1$$ since R1=R2

The voltage gain due to non-inverting channel is,

$$A_v(non-invert) = 1+\frac{R_2}{R_1}=1+1=2$$ since R1=R2

And therefore the total voltage gain from equation(1) is,

$$A_v = -1 + 2=1$$

And so in this case the output signal is same as input signal in amplitude and phase.

When the wiper is shifted to right, the amplitude decreases along with phase change. Eventually when the wiper reaches the extreme right, the amplitude of the output signal is same as the input but the sign changes to -ve, that is phase shift of 180 occurs between the output and input signal. This is because when the wiper is at extreme right side, the non-inverting terminal is connected to ground then the op-amp operates as inverting amplifier configuration with the voltage gain given by the following equation.

$$A_v(invert) = -\frac{R_2}{R_1}$$

and since the resistors are equal we have,

$$A_v(invert) = -1$$

Video demonstration

See the following video to learn how the sign changer circuit with LM358N operational amplifier works.

Applications of Sign Changer Circuit with Op-Amp

The Sign Changer Circuit with Op-Amp has the following applications:

• It is used in signal processing circuits to invert or change the polarity of a signal.
• It is used in audio amplifier to change the phase of the audio signal.
• It is used in instrumentation circuits to measure the response of a system to a negative stimulus.

Conclusion

The Sign Changer Circuit with Op-Amp is a simple and efficient circuit for changing the sign of an input signal. It can also be called as phase shifter circuit. The circuit provides a high level of accuracy and can be easily implemented using a few components. The circuit finds applications in various fields like signal processing, audio amplifiers, and instrumentation amplifier circuits.