Method and apparatus for testing electrical and electronic circuits

Abstract

An apparatus is disclosed for quickly testing individual wiring nets in a multi-layer device carrier. A central processing unit (CPU) controls a probe to sequentially engage contact pads on the carrier, each of which is electrically connected to a respective wiring net. The probe connects each wiring net to a network sensitive pulse generator circuit which generates a train of output pulses having a frequency dependent upon the transient behavior of the net under test. The stimulation of the net and the sensing of the net's response operate responsively to a feedback signal, which is also a signature signal. By connecting the net under test to the novel circuit, the combination of the novel circuit and the net under test generates the series of output pulses. The number of pulses generated in a predetermined period of time forms the signature of the net under test. A preferred embodiment is described which uses differential amplifiers to stimulate the net and to sense the net's response. The differential amplifier which senses the net's response is connected to a circuit which produces the feedback/signature signal. The feedback/signal is then provided to the differential amplifiers to adjust their behavior. A novel pulse counting and interface circuit counts each series of output pulses received from the network sensitive pulse generator in a predetermined period of time; and, under control of the CPU, transfers each count to the CPU for evaluation by programs contained therein.