The selectable gain differential amplifier includes a differential amplifier, a plurality of cascade leg pairs connected to the differential amplifier, each leg of each cascode pair including a cascode device and a load resistor configured to provide a selectable gain. A variable voltage generator is connected to each leg configured to set gain resistor voltage of any active cascode leg pair to a uniform predetermined common mode voltage and the output node voltage of any inactive cascode leg pair to a voltage different from the predetermined common mode voltage. A selector circuit is configured to select the output of any said cascode leg pair.