Analog Multiplier - Voltage-controlled Amplifier Versus Analog Multiplier

Voltage-controlled Amplifier Versus Analog Multiplier

If one input of an analog multiplier is held at a steady state voltage, a signal at the second input will be scaled in proportion to the level on the fixed input. In this case the analog multiplier may be considered to be a voltage controlled amplifier. Obvious applications would be for electronic volume control and automatic gain control. Although analog multipliers are often used for such applications, voltage-controlled amplifiers are not necessarily true analog multipliers. For example, an integrated circuit designed to be used as a volume control may have a signal input designed for 1 Vp-p, and a control input designed for 0-5 V dc; that is, the two inputs are not symmetrical and the control input will have a limited bandwidth.

By contrast, in what is generally considered to be a true analog multiplier, the two signal inputs have identical characteristics. Applications specific to a true analog multiplier are those where both inputs are signals, for example in a frequency mixer or an analog circuit to implement a discrete Fourier transform.

A four-quadrant multiplier is one where inputs and outputs may swing positive and negative. Many multipliers only work in 2 quadrants (one input may only have one polarity), or single quadrant (inputs and outputs have only one polarity, usually all positive).