Voltage controlled resistor

A voltage controlled resistor circuit, comprising:

• an operational transconductance amplifier having an inverting input, a non-inverting input adpated to be coupled to a first source of supply voltage, a diode bias input, a bias input for receiving a gain control current, first and second power supply terminals adapted to be coupled to second and third supply voltages, respectively, and an output for exibiting a high output impedance when the gain control current is substantially zero, said output impedance decreasing as said gain control current increases, said operational transconductance amplifier having first and second linearizing diodes each having an anode coupled to said diode bias input, said first linearizing diode having a cathode coupled to said inverting input and said second linearizing diode having a cathode coupled to said non-inverting input;
• first means coupled to said output for providing a low impedance buffered output;
• first impedance means coupled to said diode bias input for producing current flow through said first and second linearizing diodes;
• second impedance means coupled to said low impedance buffered output for providing feedback to said inverting input and for supplying and controlling bias current to said first linearizing diode;
• and
• third impedance means coupled between said output and said diode bias input for maintaining bias to said first means when said output approaches open circuit output impedance conditions.