Abstract: A test circuit (10) provides high and low reference voltages to a circuit (92) under test. A load (52) is connected to a multiplexed terminal (90) of circuit (92). A current source transistor (48) and a current sink transistor (132) are connected to provide current through load (52). A feedback network is connected to the current source transistor (48) and a second feedback network is connected to the current sink transistor (132). The feedback signals are compared to the reference voltages to generate control signals for driving the multiplexed terminal (90) accurately to the desired reference voltage. When the circuit (92) under test generates logic signals the load (52) sources or sinks the appropriate current depending upon the voltage states generated by the circuit (92). The voltage states generated at the multiplexed terminal (90) are transmitted through a buffer (148) to an output terminal (156).

Abstract: A multipin coupler (50) includes upper and lower ring members (52, 54) with a plurality of cooperating pin connections (76) surrounding central openings therethrough such that the circuitry and corresponding probe card for testing an IC chip can be interconnected through leads of the same lengths having uniform impedances. Guide pins (68) are provided to assure proper alignment of the ring members (52, 54) before engagement of the pin connections (76). A pin and slot connection supports the upper ring member (52) for limited movement relative to the lower ring member (54) for adjustability.