Circuit-Delay Test Instrument

The evaluation of signal propagation delay in multiple-input multiple-output digital circuits can be very time consuming. For a circuit with n inputs there are 2ⁿ different input address states and 2ⁿ(2ⁿ - 1) different input address state transitions, each of which may result in a different propagation-delay time. A circuit-delay tester has been designed and built to test signal propagation delay automatically and at high speed for all possible input state transitions. While designed primarily for testing high-speed integrated read-only memories, other applications are also possible. The tester drives up to 10 inputs and checks up to 4 outputs with continuously variable input voltage levels and output voltage thresholds. The operating speed is 1 ??s per input address transition (i.e., about 0.25 s for a complete test of a 4 ?? 256-bit ROM), while an address transition rate of 10-MHz max is simulated. The propagation-delay measurement range is 15-100 ns with an accuracy of ?? 1 ns. The tested delays are either compared against a preset value and a pass-fail status is indicated or the largest delay is located, measured, and displayed. Also, any desired input address transition can be manually selected and the related delay measured. Operation of the circuit-delay tester does not require knowledge of the logic contents of the device under test.