A Programmable Approximate Calculation Unit Employing Time-Encoded Stochastic Computing Elements

A programmable calculation unit is proposed on the basis of piece-wise linear approximation. An arbitrary function with single variable is approximately retrieved by piece-wise linear segmentation where parameters for each segment are pre-stored in a look-up table. An improved scheme of time_encoded stochastic computing elements is developed to efficiently carry out the multiplication and summation of a specific segment. The storage of piece-wise linear parameters is realized by a set of compact multi-valued logic flip-flops. The entire calculation processor is designed with 588 MOS transistors in a 0.18um CMOS technology. For proof-of-concept, three of commonly applied non-linear functions including Tanh, exponential, and rectified linear unit are demonstrated as examples. From circuit simulation results, all the exampled functions are retrieved with the average error less than 2.1% by the proposed processor consuming the energy of 2.78pJ in maximum. The calculation speed reaches ~36x of the state-of-art works.