A transconductance amplifier (also known as a transconductance op-amp or OTA - Operational Transconductance Amplifier) is a type of electronic amplifier that converts an input voltage signal into an output current. Unlike traditional voltage amplifiers, which amplify voltage signals, the transconductance amplifier's primary function is to control the output current based on the input voltage.
The basic symbol for a transconductance amplifier looks similar to a regular op-amp, with two input terminals and one output terminal. However, the functional block diagram and the way it operates are different.
In a transconductance amplifier, the input voltage is typically applied to one of the input terminals (called the "input voltage" terminal), and the output current is generated at the output terminal. The other input terminal (called the "control voltage" terminal) is used to set the gain or transconductance of the amplifier.
Mathematically, the output current (I_out) of the transconductance amplifier can be represented as:
I_out = Gm * V_in
where:
I_out is the output current.
Gm is the transconductance (gain) of the amplifier.
V_in is the input voltage applied to the "input voltage" terminal.
Transconductance (Gm) is a measure of how much output current changes in response to a change in the input voltage. It is usually expressed in units of siemens (S) or amperes per volt (A/V).
Transconductance amplifiers find various applications in electronics and signal processing, particularly in voltage-controlled systems, oscillators, filters, and other circuits where precise control of current based on input voltage is required. They are essential components in many analog circuits, and their versatility makes them valuable in a wide range of applications.