The voltage controlled amplifiers are electronic amplifiers that will varies its gain depending on the control voltage ( CV ). For more clarity the processor that will alter the amplitude of the signal proportional to the control voltage applied to its amplitude modulation.

The VCAs have many applications such as that are listed below.

- Audio level compression
- Synthesizers
- Amplitude modulation

### Explanations

Lets to understand how the VCA works. From the name it is clear that amplification factor of the amplifier is controled by the voltage. For the explanation we are taking an op-amp and we are using non inverting mode as like the Vin applied on the positive pin and in negative pin of the op amp we are connecting the feed back resistors.

**R1** and **R2** resistors are connected series from the **Vout** to ground and the middle connection **Vin 2** connected. from the fundamentals of electronics says that the Vin2 is equation with the voltage devider resistors of R1and R2.

**Vin2 = Vout *R2/R1+R2**

As comparing the Vin1 and Vin 2 their is small difference in the voltage so we can replace the Vin 2 with Vin1. so the equation is changes to,

**Vin1 = Vout*R2/R1+R2**

And ,

**Vout/Vin = R1+R2/R2** that is equals **1+R1/R2**

This equations solves that Positive quantity so is known as non inverting amplifier.

Ok this is the common circuit basics you know, in VCA the R2 resistor is replaced with the Mosfet. So the R1 is depending on the voltage given to the gate potential. If **increase the gate source potential the resitance R2 decreases and the overall gain increases**. as per the equation 1+R1/R2.

So this type of operational amplifiers are known as Voltage controller amplifiers.