Test Methodology for Detecting Missing Emitter Follower Resistors for Differential Current Switch Circuits
Original Publication Date: 1987-Aug-01
Included in the Prior Art Database: 2005-Feb-01
A method is described for detecting missing emitter follower pull-down resistors in a differential cascode current switch circuit (DCS circuit) such as is shown in the drawing. The emitter follower pull-down resistors are REL, RER, RSL and RSR. If any of these resistors is missing, or the metal lines broken at the arrows 10, this circuit fails. This failure is a delay failure, and under normal operating conditions, it is not DC detectable, meaning the steady-state voltage levels on the chip outputs do not indicate a failure. The method described herein enables DC detection of such faults. In practice, standard stuck-fault or random patterns may be used to test for these faults, along with other stuck faults on a standard LT tester.