Patent ID: 7076222

Claim:
An automatic gain control loop for a radio receiver, comprising a voltage controlled amplifier receiving an analog input signal of the automatic gain control loop and a gain control signal to output an analog output signal which equals to the analog input signal of the automatic gain control loop amplified according to the analog gain control signal, an analog/digital converter receiving the analog output signal and converting it to a digital output signal, a digital control circuit to determine a digital gain control signal on basis of the digital output signal, a digital/analog converter receiving the digital gain control signal and converting it to said analog gain control signal, a switchable lowpass filter receiving said analog gain control signal and generating said gain control signal which is filtered by said switchable lowpass filter before being supplied to said voltage controlled amplifier, a switching control unit receiving said digital gain control signal and generating a switching control signal for switching said switchable lowpass filter to a low time constant which is lower than a predetermined time constant, said switching control unit including a differentiator receiving said digital gain control signal, and a threshold decision unit supplying said switching control signal in case a change of the gain, control, signal of the automatic gain control loop lies above a predetermined threshold, and a hold unit which switches the time constant of said switchable lowpass filter after said change of the gain control signal lies below said predetermined threshold to a low time constant, which holds said low time constant for a predetermined time and which switches to a higher or another time constant after said predetermined time.