Voltage Controlled Resistor Circuit

A voltage controlled resistor can be used to change the frequency of an oscillator.

Voltage controlled resistor circuit. The basic circuit forms a voltage divider as shown in figures 3 4 5 and 6. Basic voltage controlled resistor vcr circuits one of the simplest uses of a voltage controlled resistor is an electronically controlled attenuator or volume control. Two types of fets are often used. When a voltage controls the frequency of an oscillator it is called a voltage controlled oscillator or vco for short.

One side of the load resistance is connected directly to ground. Vcrs are most often built with field effect transistors. Here s a subcircuit for this device subckt vc res1 10k 1 2 4 5 eres 1 3 value i vsense 10k v 4 5 vsense 3 2 dc 0v ends. In addition to the other fine ideas you could use a voltage controlled oscillator to produce a clock of variable frequency and then use switched capacitor techniques to produce an effective resistor that varies with clock frequency.

It is voltage controlled and bidirectional the magnitude and direction of the load current are determined by the magnitude and polarity of the input voltage. Vcos are used in fm modulation mainly. There are two distinct regions. The field effect transistor as a voltage controlled resistor we consider the use of a n channel fet as a voltage controlled resistor where the resistance between the drain and source is controlled by the gate source voltage.

This type of circuit is commonly used in electronics to drive current controlled devices like bjt scr etc. The voltage gain is easily found by voltage division to be v o v s r on r on r 1 1 r r on 1 1 k n r v gg v tn 4 17 by adjusting the value of v. The input port voltage controls the value of the resistor between the output ports. A voltage controlled resistor is a three terminal active device with one input port and two output ports.

A simple addition to the above resistor model gives you a voltage controlled resistor. As one example the circuit in fig. In this case it used to make a two tone siren which you can see in operation in the video below. The jfet and the mosfet.

All you need is a controlling voltage to multiply the resistor value. Floating vcrs can be placed between two passive or active components. It is ground referenced. 4 8 a shown conceptually in fig.

In a voltage controlled current source circuit as the name implies a small amount of voltage across the input will proportionally control the current flow across the output loads. 4 8 b represents a voltage controlled attenuator in which the voltage transfer through the circuit can be varied electronically. V i x r x vc.