Editing Variable-gain amplifier (section)

== Digital variable-gain amplifier ==

A '''digitally controlled amplifier''' (DCA) is a variable-gain amplifier that is digitally controlled.

The digitally controlled amplifier uses a stepped approach giving the circuit graduated increments of gain selection.  This can be done in several fashions, but certain elements remain in any design.

At its most basic form, a toggle switch strapped across the feedback resistor can provide two discrete gain settings.  While this is not a computer-controlled function, it describes the core function.  With eight switches and eight resistors in the feedback loop, each switch can enable a particular resistor to control the amplifier's feedback.  If each switch was converted to a relay, a microcontroller could be used to activate the relays to attain the desired amount of gain.

Relays can be replaced with Field Effect Transistors of an appropriate type to reduce the mechanical nature of the design.  Other devices such as the CD4053 bi-directional CMOS analog multiplexer integrated circuit and digital potentiometers (combined resistor string and MUXes) can serve well as the switching function.

To minimize the number of switches and resistors, combinations of resistance values can be utilized by activating multiple switches.