Multi-degree smoother for low power consumption in single and multiple scan-chains BIST

This paper presents a smoothing technique for the output sequence of linear feedback shift registers (LFSR) to reduce power consumption in test-per-scan built-in self-test (BIST) applications. The proposed smoother is implemented by adding one multiplexer between the LFSR and scan-chain input of a single scan-chain. The size of the multiplexer is determined the desired smoothing degree. When the smoothed sequence of the LFSR is used to feed the test patterns in test-per-scan BIST, it reduces the number of transitions that occur at scan-chain input during scan shift operations by 25% to 50% depending on the smoothing degree, and hence reduces switching activity in the circuit-under-test (CUT) during test application. The proposed technique can be extended to multiple scan-chains BIST, also to test-per-clock applications. Various properties of the proposed technique and the methodology of the design are presented in this paper. Experimental results for the ISCAS´89 benchmark circuits show that the proposed design can reduce the switching activity up to 55% with a negligible effect on the fault coverage and test application time.