Automatic gain control circuit for signal with diverse power level range

Abstract

An automatic gain control circuit for amplifying an input signal of varying strength and having a fast attack mode of operation and a tracking mode of operation includes a gain controlled amplifier for receiving the input signal and producing an amplified analog output signal, a receive signal strength indicator (RSSI) circuit for receiving the amplified analog signal and producing an output voltage indicative of strength of the signal, and decision logic circuitry responsive to the output voltage from the RSSI circuit for controlling gain to the gain controlled amplifier. A plurality of comparators is provided for comparing the output voltage from the RSSI circuit to threshold voltages in generating output signals indicative of the voltage comparisons which can indicate the RSSI output voltage being very low, low, high, or very high as inputs to the decision logic circuit. The decision logic circuitry can then provide a fast acquisition mode of operation or a tracking mode of operation depending on the output signals from the plurality of comparators. In preferred embodiments, the gain controlled amplifier can comprise a plurality of cascaded gain controlled amplifier circuits with the gains of the cascaded gain control amplifier circuits being controlled by the decision logic circuitry. The threshold voltages provided to the plurality of comparators can be programmable for specific modes of operation.