Low voltage variable gain amplifier having constant common mode DC output

A differential variable gain amplifier comprising:

• a differential voltage signal input;
• a differential gain control input;
• a differential voltage signal output;
• first and second load resistors which are coupled to respective terminals of the differential voltage signal output;
• conversion means for converting the differential voltage signal input to a differential input current;
• variable gain means for producing a differential output current and a DC compensation current from the differential input current based on the differential gain control input;
• output means for feeding the differential output current through the first and second load resistors;
• and
• DC compensation means for injecting the DC compensation current into the first and second load resistors.

A method of varying gain from a differential voltage input signal to a differential voltage output signal based on a differential gain control signal, the method comprising:

• converting the differential voltage input signal to a differential input current having first and second input current legs;
• selectively steering current away from the first and second input current legs based on the differential gain control signal to produce first and second variable output currents, respectively, and first and second compensation currents, respectively;
• feeding the first and second variable output currents through the first and second load resistors, respectively;
• and
• summing the first and second output currents to produce a DC compensation current and injecting the DC compensation current into the first and second load resistors.