Programmable instrumentation amplifier

A first amplifier channel between an input and output includes an input transistor emitter and a first output transistor emitter connected together to form a first emitter pair. A current source is connected to the emitter pair via a transistor which is controlled by a latch. Programming the latch permits the channel to be turned on or off. The emitter pair is connected to a positive voltage through a resistor and to ground through a diode to force it to a controlled off voltage, which prevents signals from passing when the channel is off. There is a output driver amplifier in a feedback circuit. An outdisable circuit controls the voltage and current of the output driver amplifier to place the output in a state in which it appears electrically as an open circuit when the channel is off. Multiple programmable amplifiers can be combined to make a multiplexer, a selectable gain circuit, or a selectable attenuation circuit, all with high band width and high signal integrity.