OBT implementation on Gm-C filters without self-tuning capability

This paper presents an Oscillation Based Test (OBT) scheme applied to a Gm-C band pass filter lacking an on-chip automatic tuning system. The fact of dealing with untuned filters prevents careless application of the traditional OBT. This is because, as a consequence of the process parameters dispersion, the use of one unique and fixed reference oscillation frequency for evaluating the test results is no longer practical. In order to overcome this problem a new approach based on the relative comparison of two oscillation frequencies is proposed. In order to evaluate the effectiveness of the idea, catastrophic fault models at both, device and circuit level, have been adopted. The results are encouraging, despite the circuit complexity introduced for adapting the classical OBT to untuned filters.