A Pragmatic Approach to Testing Mixed Analogue/Digital Circuits

The increased use of mixed analogue/digital circuits in VLSI designs has increased, enormously, the problems of testing these complex circuits. The problem is further compounded when these types of circuits are used in safety critical applications where there is a need to detect intermittent faults. The problem of intermittent fault detection has been solved to some extent for digital circuits, but remains a serious problem in analogue circuits. A pragmatic approach, called Residual Multiple Frequency Testing, is proposed for concurrent error detection in analogue circuits in which two pilot signals whose frequency lies, just outside, the operational bandwidth of the analogue circuit under test are continually monitored. Fluctuations in the output level of these pilot signals indicates a fault in the circuit. The format of the two rail error signal from the checking hardware is effectively compatible with that used in digital circuits.