Patent ID: 6842071
Filing Date: 2005-01-11
Classification: H03F,H03G

Abstract:
1. A variable gain amplifier comprising: a main input terminal for receiving an input signal to be amplified, a main output terminal for outputting the amplified signal, N selectively selectable gain stages, where N is an integer greater than one, for amplifying the input signal, the gain stages having respective signal outputs for providing the amplified input signal to the main output terminal, a first of the N gain stages being coupled to the main input terminal, a voltage divider impedance chain, a first end of which is coupled to the main input terminal, the voltage divider impedance chain having (N-1) output taps coupled to respective ones of the gain stages from a second one to an Nth one of the N gain stages for applying the input signal to the gain stages from the second to Nth gain stage progressively attenuated from the second gain stage to the Nth gain stage, a selectively operable shunt-shunt feedback circuit for feeding back the amplified input signal from at least one of the gain stages to the main input terminal for varying the input impedance of the variable gain amplifier, at least one passive shunt impedance element selectively switchable to the main input terminal for varying the input impedance of the variable gain amplifier, and a control circuit for selecting the feedback circuit and the at least one passive shunt impedance element in response to the selected gain stage for maintaining the input impedance of the variable gain amplifier within a predetermined input impedance range.