A 168-mW 2.4-Real-Time 60-kWord Continuous Speech Recognition Processor VLSI

Guangji HE
Takanobu SUGAHARA
Yuki MIYAMOTO
Shintaro IZUMI
Hiroshi KAWAGUCHI
Masahiko YOSHIMOTO

Publication
IEICE TRANSACTIONS on Electronics   Vol.E96-C    No.4    pp.444-453
Publication Date: 2013/04/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E96.C.444
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Solid-State Circuit Design—Architecture, Circuit, Device and Design Methodology)
Category: 
Keyword: 
40 nm VLSI,  hidden Markov model (HMM),  large vocabulary continuous recognition (LVCSR),  

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Summary: 
This paper describes a low-power VLSI chip for speaker-independent 60-kWord continuous speech recognition based on a context-dependent Hidden Markov Model (HMM). It features a compression-decoding scheme to reduce the external memory bandwidth for Gaussian Mixture Model (GMM) computation and multi-path Viterbi transition units. We optimize the internal SRAM size using the max-approximation GMM calculation and adjusting the number of look-ahead frames. The test chip, fabricated in 40 nm CMOS technology, occupies 1.77 mm2.18 mm containing 2.52 M transistors for logic and 4.29 Mbit on-chip memory. The measured results show that our implementation achieves 34.2% required frequency reduction (83.3 MHz), 48.5% power consumption reduction (74.14 mW) for 60 k-Word real-time continuous speech recognition compared to the previous work while 30% of the area is saved with recognition accuracy of 90.9%. This chip can maximally process 2.4faster than real-time at 200 MHz and 1.1 V with power consumption of 168 mW. By increasing the beam width, better recognition accuracy (91.45%) can be achieved. In that case, the power consumption for real-time processing is increased to 97.4 mW and the max-performance is decreased to 2.08because of the increased computation workload.