Patent ID: 6583671
Filing Date: 2003-06-24
Classification: H03F

Abstract:
An automatic gain control (AGC) circuit, comprising:a gain stage having, a gain stage amplifier coupled to an input of the AGC circuit, a gain stage current source configured to bias the gain stage amplifier, and a gain control mechanism coupled to the gain stage amplifier and configured to vary a gain of the gain stage amplifier; and a gain control circuit having an input coupled to an output of the gain stage amplifier and configured to produce a gain control voltage based on the output of the gain stage amplifier, said gain control voltage is coupled to the gain control mechanism and used to adjust the gain of the gain control mechanism; wherein: said gain stage amplifier is a transistor having a gate connected to the input of the AGC circuit; said gain control mechanism is a variable feedback resistor having an amount of resistance controlled by the output voltage of said gain control circuit; said variable feedback resistor comprises a FET transistor in parallel with a resistor, a gate of the FET connected to the output voltage of said gain control circuit; and said variable feedback resistor connected between a collector and base of said gain stage amplifier.