AUTOMATIC GAIN CONTROL CIRCUIT AND AN RF RECEIVER AND METHOD USING SUCH A CIRCUIT

摘要

An automatic gain control (AGC) circuit comprising: a forward transmission path having, in use, applied at its input an input RF signal and to provide at its output an output signal; a variable gain AGC amplifier in the forward transmission path for processing the input RF signal, which amplifier has a control input and is responsive to a control signal applied at its control input to vary its gain; a feedback loop, coupled from te output of said forward transmission path and to said control input of said AGC amplifier, said feedback loop including a signal detector that has a predetermined non-linear gain response, depending on an input signal level, the gain being higher for greater input signal strength, an integrator, coupled to said control input of said amplifier; and a voltage source, coupled to said integrator and to said control input of said amplifier, the circuit being characterised by the fact that it also includes a further variable gain device for varying the gain or attenuation of a signal applied as an input signal to the control input of said AGC amplifier.