Patent ID: 7512851

Claim:
A method for time-division demultiplexing and decompressing a compressed input stimulus, provided at a selected data-rate R 1 , into a decompressed stimulus, driven at a selected data-rate R 2 , for driving selected scan chains in a scan-based integrated circuit during scan-test mode, the scan-based integrated circuit containing a plurality of time-division demultiplexors (TDDMs), a plurality of decompressors, a plurality of compressors, a plurality of time-division multiplexors (TDMs), at least one high-speed clock CK 1 , at least one low-speed clock CK 2 , and a plurality of scan chains, each scan chain comprising multiple scan cells coupled in series; said method comprising: (a) generating, shifting in, demultiplexing and decompressing said compressed input stimulus through said time-division demultiplexors and said decompressors as said decompressed stimulus to all said scan cells in said scan-based integrated circuit during a shift-in operation; (b) capturing a test response to all said scan cells during a selected capture operation; (c) compressing, multiplexing and shifting out said test response or said decompressed stimulus through said compressors and said time-division multiplexors as a compressed test response, while shifting in a new decompressed stimulus to all said scan cells, during a shift-out operation; and (d) repeating steps (b) to (c) until a predetermined criterion is reached wherein, by using both time-division demultiplexor and multiplexor pairs and decompressor and compressor pairs in combination, test data volume is reduced and effects of test time reduction are multiplied in comparison with effects of test time reduction achievable by separate use of time-division demultiplexor and multiplexor pairs and decompressor and compressor pairs.