Testing a PWM circuit using functional fault models and compact test vectors for operational amplifiers

The use of analog VLSI technology on ordinary but complex electronic products has in the test one of its last frontiers. The design for testability paradigm should allow the test plan implementation early in the design cycle. However, in a successful test strategy, fault simulation should be carried out in order to evaluate appropriate test patterns, fault grade, etc. This way adequate fault models must be established. This paper shows the suitability and the straightforward consequences on testing of complex analog circuits when using OpAmp functional fault macromodels. Due to the lack of fault models, suitable for operational amplifiers fault simulation, we propose methodology for functional fault modeling and a method for test pattern generation. A fault dictionary for OpAmps is built and a procedure for compact test vector construction is proposed. The method is used to detect OpAmp faults in a pulse width modulator. The obtained results show that the proposed method is able to verify high level OpAmp requirements, such as open loop gain, slew-rate and CMMR, with good compromise between fault modeling and the analog circuit simulation complexity.