All Digital Low-Cost Built-in Defect Testing Strategy for Operational Amplifiers with High Coverage

Backed by standards like ISO26262, achieving near 100% defect coverage is becoming a common reliability requirement in the ever-growing automotive industry. However, achieving high defect coverage in an analog circuit has been proven to be a difficult/expensive task even with sophisticated analog and digital testing circuitry. In this work, we present a simple design for testability (DfT) technique that achieves 98% defect coverage for operational amplifiers including Widlar current reference and biasing circuitry. Our robust testing method utilizes purely digital testing circuits and is extremely time-efficient reducing the test cost. The proposed method can be used both at production test and for on-line health monitoring post-deployment to detect zero-time and latent defects. Also, the digital nature of our method presents a way for defect localization through the recorded bit streams. In this work, we also introduce a simple method to detect defects in the Widlar current reference and the bias current circuit. We validate all our results using extensive transistor-level simulations in UMC65nm technology.