a driver circuit for regulating the current flowing through the coils of a rotary field microwave phase shifter . the circuit includes logic circuitry functions which implements an algorithm to provide decision making capability to avoid failure - inducing conditions , reducing power consumption , and enhancing testability of the circuit . the circuit includes two switches that respectively drive either a positive or a negative voltage to the load , to begin steering the load current to the appropriate direction . the logic circuitry includes a current mode mapping function to determine whether a commanded current value requires positive , negative or no voltage applied to the load . the logic circuitry further includes a finite state machine to control the two switches , to ensure that both switches are never commanded to be conductive at the same time , and to permit toggling of only one of the switches to regulate the current to a target value in a feedback loop . the state machine also provides a test function which disables the current feedback loop of the circuit and generates deterministic patterns for tracing circuit activity .