A circuit for alternatively controlling a current through a device and permitting measurement of a voltage across the device or controlling a voltage across the device and permitting measurement of a current through the device includes a sense impedance in series combination with the device; a buffer communicating with a common point between the sense impedance and the device; a current output stage; and a voltage output stage. When the circuit is controlling the current through the device, the voltage output stage forces the common point to a virtual ground and the current output stage forces a desired current through the device in response to a signal from the buffer. When the circuit is controlling the voltage across the device, the current output stage forces the common point to a virtual ground and the voltage output stage forces a desired voltage across the device in response to the signal from the buffer.