A method and apparatus for automatically controlling the gain of a digital
radio receiving circuit in which a single set of analogue amplifiers is
used as the front end to feed two separate digital back-end, demodulating
circuits, and in which, for optimal performance, each of the two digital
demodulating circuits require the front end analogue amplifiers to
operate over a significantly different dynamic range. An
automatic-gain-control selector selects one of two automatic-gain control
signals to set the gain of the analogue amplifier. In addition, the
automatic-gain-control selector sets a compensatory gain of a digital
automatic gain control in the back-end circuit not selected, so that the
unselected demodulating circuit has substantially the same input signal
as if it had been selected. In this way, both demodulating circuits can
process the input signal as if they were in control of the analogue
amplifier.