Practical considerations in applying Σ-Δ modulation-based analog BIST to sampled-data systems

The analog built-in self-test (BIST) scheme, with stimulus generation and response extraction based on the Σ-Δ modulation, is proven to be quite effective for sampled-data systems. We show that the Σ-Δ modulators can be selected optimally for certain applications and functional tests. The criteria for valid tests are also derived. In particular, a valid frequency response test is determined by the frequency response observation range FROR_BIST(z) of the BIST circuit. Given the transfer function H_CUT(z) of the circuit under test, the requirement becomes FROR_BIST(z)≫|1/H_CUT(z)|. Using the MOSIS 0.35-μm CMOS process, we have implemented a test chip containing a Fleischer-Laker biquadratic low-pass filter as the circuit under test. An on-chip one-bit digital-to-analog converter provides the analog stimulus from a bit stream which is applied externally. For each test item, different bit streams, synthesized by first-, second-, and fourth-order Σ-Δ modulators that are programmed by software, are compared for performance. First- and second-order Σ-Δ modulators are implemented on the test chip as the candidates for the analog response extractor. The measurement results by single-tone tests and multitone tests validate the feasibility of the BIST scheme.