INTEGRATED CIRCUIT RADIO FREQUENCY AMPLIFIER WITH NOTCH FILTER

摘要

An integrated circuit superheterodyne radio receiver includes a notch filter coupled with an amplifier for amplifying radio frequency (RF) signals to improve image signal rejection. The notch filter includes a first oscillator circuit with a tank circuit having a resonant frequency corresponding to the unwanted image frequency signal. A control circuit includes a second oscillator circuit, a master bias circuit and a slave bias circuit. The second oscillator circuit is substantially similar to the first oscillator circuit. The master bias circuit is responsive to an amplitude of oscillatory signals in the second oscillator circuit for limiting a flow operating current such that the second oscillator circuit is retrained to operate in a marginally oscillatory state. A slave bias circuit is responsive to the master bias circuit for similary limiting a flow of current, for operating the first oscillator circuit. A coupling transformer is connected between the amplifier and the first oscillator circuit for exchanging signal energies between the first oscillator circuit and the amplifier such that the first oscillator circuit is reduced to a marginally quiescent state of operation while loaded by the amplifier. An input impedance of the amplifier is thereby raised at frequencies near the image signal frequency, improving the image signal rejection.