Patent ID: 7565124

Claim:
An automatic gain control circuit including a receiving unit for receiving an RF signal and a gain amplifier for controlling the gain of the receiving unit, wherein the receiving unit comprises an amplification part including a low noise amplifier and a gain amplifier configured to amplify the RF signal, a mixer configured to down-convert and tune the RF signal output from the gain amplifier, a low pass filter configured to receive the down-converted signal from the mixer, and an intermediate frequency variable gain amplifier configured to amplify the signal filtered by the low pass filter to an intermediate frequency signal, and; wherein the gain control unit comprises a received signal strength indicator connected to the output port of the low pass filter and configured to detect the level of the output signal of the low pass filter, a first comparator configured to compare the output signal level detected by the received signal strength indicator with a first reference signal level, a power detector configured to detect the output signal level of the amplification part of the receiving unit, a second comparator configured to compare the output signal level detected by the power detector with a second reference signal level, and a gain controller-configured to increase, decrease or hold the gain in response to the signals output from the first and second comparators, wherein the power detector includes an input resistor part, a programmable gain amplifier, an envelope detector and an output resistor part.