Digital bus faults measuring techniques

This paper describes techniques available today to detect digital bus faults on electronic PCB's using in-circuit testers. The paper will also suggest a new test technique called "CLIPS" developed using a Teradyne Z1890 ICT tester. The CLIPS uses a vector technique in which dynamic pulses are applied to the bus lines at high speed. The current pulse responses are picked up by specially designed current sensors, which are amplified and dynamically compared to pre-determined threshold levels. This technique is very fast and back-drive is very short. This makes it much safer to the board and components under test. The tests are run with different bus devices which enabled, at different threshold levels and different "expect" values, to find and diagnose the respective fault. The CLIPS uses specially designed current sensors and amplifier circuits, which perform a differentiation followed by an integration function. This makes the measurements much less sensitive to noise, voltage polarity, and current drift and temperature changes. In concept this technique can be applied to any make of Digital In-Circuit tester.