Time-Encoded Values for Highly Efficient Stochastic Circuits

M. Hassan Najafi, Shiva Jamali-Zavareh, David J. Lilja, Marc D. Riedel, Kia Bazargan, Ramesh Harjani

Research output: Contribution to journalArticlepeer-review

44 Scopus citations


Stochastic computing (SC) is a promising technique for applications that require low area overhead and fault tolerance, but can tolerate relatively high latency. In the SC paradigm, logical computation is performed on randomized bit streams. In prior work, streams were generated with linear feedback shift registers; these contributed heavily to the hardware cost and consumed a significant amount of power. This paper introduces a new approach for encoding signal values: computation is performed on analog periodic pulse signals. Exploiting pulse width modulation, time-encoded signals corresponding to specific values are generated by adjusting the frequency and duty cycles of pulse width modulated (PWM) signals. With this approach, the latency, area, and energy consumption are all greatly reduced. Experimental results on image processing applications show up to 99% performance speedup, 98% saving in energy dissipation, and 40% area reduction compared to prior stochastic approaches. Circuits synthesized with the proposed approach can work as fast and energy-efficiently as a conventional binary design while retaining the fault-tolerance and low-cost advantages of conventional stochastic designs.

Original languageEnglish (US)
Article number7822930
Pages (from-to)1644-1657
Number of pages14
JournalIEEE Transactions on Very Large Scale Integration (VLSI) Systems
Issue number5
StatePublished - May 2017

Bibliographical note

Funding Information:
This work was supported by the National Science Foundation under Grant CCF-1408123.

Publisher Copyright:
© 2017 IEEE.


  • Energy-efficient computing
  • mixed-signal design
  • pulse width modulation
  • stochastic computing (SC) circuits
  • stochastic number generator (SNG)
  • time-encoded values


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