Open Emitter Follower Detection Enhancement
Original Publication Date: 1987-Aug-01
Included in the Prior Art Database: 2005-Feb-01
A common problem associated with current switch / emitter follower circuits is the detection of "open" defects in the emitter follower output stage. An "open" defect in the DC bias path ("pull-down") of the emitter follower will not result in a DC circuit failure. Hence, this defect can not be detected with a standard DC test. Unfortunately, this defect will degrade the circuit's transient performance very significantly. The down-going transition will increase by a factor of typically 10-100. On a very large-scale integrated chip, which contains thousands of emitter followers, it is important to detect these "open" defects. However, it is also desirable to avoid additional AC testing. A method to accomplish these goals is described below. The current technique for detecting "open" emitter followers is shown in Fig. 1.