Transconductance amplifier having a digitally variable transconductance as well as a variable gain stage and an automatic gain control circuit comprising such a variable gain stage

A variable gain stage comprising:

• a transconductance operational amplifier having a non-inverting and an inverting input terminal, an output terminal and a gain control input, said gain stage comprising a resistive ladder coupled between said output terminal and a reference terminal, said inverting input terminal being selectively connectable to one of a plurality of taps of said resistive ladder in response to a binary gain control signal applied to said gain control input for digitally controlling the gain of said variable gain stage, wherein said transconductance operational amplifier comprises:
• a differential stage having first and second inputs coupled to respective ones of said input terminals, a first differential output coupled to said output terminal via a first output branch of a first current mirror and a second differential output coupled to said output terminal via a second current mirror and a first output branch of a third current mirror, wherein said first and third current mirrors comprise further output branches, the further output branches being selectively coupled to said output terminal via respective switches for selectively supplying output currents to said output terminal in response to a binary transconductance control signal applied to said gain control input, and wherein the transconductance of said transconductance amplifier is variable in accordance with a change in the gain of said variable gain stage.