Patent ID: 7865157

Claim:
An RF-circuit including an amplifier and a controllable mixer, the controllable mixer having at least one mixing transistor, wherein the at least one mixing transistor is a bipolar transistor, wherein an oscillator signal and an input signal are supplied to the mixing transistor, wherein the input signal comprises a useful signal and further signals, and wherein the mixer provides an output signal to a demodulator, which demodulator provides a demodulated output signal, wherein a controller is provided, which applies a control signal to the mixing transistor as a function of a signal quality of the demodulated output signal, wherein an operating point of the at least one mixing transistor can be set by means of the control signal, wherein an intermodulation immunity and/or a noise of the mixer can be varied as a function of the operating point of the at least one transistor, wherein a gain of the at least one mixing transistor increases and the intermodulation immunity decreases when the operating point is set such that a collector current is reduced, and wherein the gain of the at least one mixing transistor decreases and the intermodulation immunity increases when the operating point is set such that the collector current is increased, and wherein a controllable portion of an overall gain of the RF-circuit is determined by the operating point of the at least one mixing transistor.