Voltage Controlled Resistor. Not accurate but it works and it is very cheap. A voltage controlled resistor vcr may be defined as a three terminal variable resistor where the resistance val ue between two of the terminals is controlled by a voltage potential applied to the third.
Vcos are used in fm modulation mainly. This subcircuit consists of two controlled sources and employs an external reference component that is sensed. 0 v g s v c r v gs v d r or v gs v c v ds 2 so that 1 r d s i d v ds 2 s v g 2 off d v c ds 2 v gs off.
For frequencies greater than 20 hz c1 s impedance can be considered as an ac short circuit.
One of the simplest uses of a voltage controlled resistor is an electronically controlled attenuator or volume control. The circuit uses a voltage controlled resistor x vcres. Active circuits that simulate passive components can work for some very specific applications but they don t come close to matching resistors inductors and capacitors in all respects. When a voltage controls the frequency of an oscillator it is called a voltage controlled oscillator or vco for short.
