voltage controlled amplifier (VCA)

Voltage controlled amplifiers, Voltage Controlled Amplifier(VCA) or Variable Gain Amplifier( VGA), are regulated passive or active quadrupoles. They can be voltage controlled amplifiers or voltage controlled attenuators.

The principle of voltage controlled amplifiers is based on the fact that the gain can be varied by a control voltage( CV). A simple VCA can be an operational amplifier( OpAmp) that has a variable resistor in its feedback loop, such as a thermistor, varistor,photoresistor, or voltage controlled resistor( VCR).

1. InRF technology, voltage controlled amplifiers are used to amplify the high frequency signals. The amplification factor is always above >1. The control is done by a control voltage (CV). Furthermore, VCAs can be used as modulators for amplitude modulation. Here the modulation signal corresponds to the control voltage.
2. In audio technology, VCAs are used for signal amplification and attenuation. Thus for level compression, in combination with faders and in synthesizers, but also as voltage controlled attenuators, with which the signal level can be attenuated unattenuated but also continuously, up to the totally attenuated signal level. The gain factor is thus between 1 for the unattenuated state and 0 for the total attenuation of the signal level.