A variable-gain amplifier with high input impedance includes positive and negative inputs, positive and negative outputs, first and second differential circuits and first, second and third impedances. The impedances form an impedance bridge between the outputs. The first and second differential circuits each have one input coupled to one of the inputs of the differential amplifier, one input coupled to the impedance bridge, and two outputs connected to the outputs of the differential amplifier. At least one of the impedances is a variable impedance.