Patent ID: 6873212
Filing Date: 2005-03-29
Classification: H03F

Abstract:
1. An integrated amplifier circuit, comprising; a transistor amplifier having an input for receiving radio frequency (RF) signals and amplifying received RF signals with an amplifying gain; a local oscillator for generating a local oscillator signal; a mixer for generating an intermediate signal by mixing signals from the transistor amplifier and the local oscillator; a tank circuit with a resonant frequency substantially corresponding to a frequency of an undesired RF signal; a coupling circuit for coupling the tank circuit with the transistor amplifier; and an active impedance circuit comprising: an oscillator circuit including an amplifier connected with the tank circuit such that a frequency of oscillatory operation substantially corresponds to the frequency of said undesired RF signal, a gain of the amplifier being variable through a range from a maximum gain being sufficient for oscillatory operation through a lesser gain; a gain control circuit for generating an operating gain in said range and tending toward said lesser gain, such that coupling via the coupling circuit quenches oscillatory operation and said amplifying gain of the transistor amplifier at signal frequencies near the frequency of said undesired RF signal is reduced wherein said tank circuit is a first tank circuit, said oscillator circuit is a first oscillator circuit, and wherein the gain control circuit comprises: a second tank circuit and a second oscillator circuit being substantially similar to the first tank circuit and the first oscillator circuit, respectively; a master gain control circuit for varying a gain of the second oscillator for initiating oscillatory operation of the second oscillator and thereafter altering the gain of the second oscillator in inverse relationship to an amplitude of oscillations in the second oscillator for marginally sustaining oscillatory operation of the second oscillator; and a slave gain control circuit responsive to the master gain control circuit such that said operating gain of the first oscillator substantially corresponds to the gain of the second oscillator.