The AD693 is a monolithic signal conditioning circuit which accepts low-level inputs from a variety of transducers to control a standard 420 mA, two-wire current loop. An on-chip voltage reference and auxiliary amplifier are provided for transducer excitation; up to 3.5 mA of excitation current is available when the device is operated in the loop-powered mode. Alternatively, the device may be locally powered for three-wire applications when 020 mA operation is desired.