A Method of Sequential Circuit Synthesis Using One-Hot Encoding for Single-Flux-Quantum Digital Circuits

Koji OBATA  Kazuyoshi TAKAGI  Naofumi TAKAGI  

Publication
IEICE TRANSACTIONS on Electronics   Vol.E90-C   No.12   pp.2278-2284
Publication Date: 2007/12/01
Online ISSN: 1745-1353
DOI: 10.1093/ietele/e90-c.12.2278
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Superconducting Electronics
Keyword: 
sequential circuit synthesis,  one-hot encoding,  single-flux-quantum (SFQ),  

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Summary: 
A method of sequential circuit synthesis is proposed for Single-Flux-Quantum (SFQ) digital circuits. Since all logic gates of SFQ digital circuits are driven by a clock signal, methods of sequential circuit synthesis for semiconductor digital circuits cannot derive the full power of high-throughput computation of SFQ circuit technology. In the method, a 'state module' consisting of a DFF and several AND gates is used. First, states of a sequential machine are encoded by one-hot encoding and state modules are assigned to the states one-by-one, and then, the modules are connected with each other according to the state transition. For the connection, Confluence Buffers (CBs), i.e., merger gates without clock signals are used. Consequently, gates driven by a clock signal are removed from its feedback loops, and therefore, a high-throughput SFQ sequential circuit is achieved. The experimental results on benchmark circuits show that compared with a conventional method for semiconductor digital circuits, the proposed method synthesizes circuits that work with 4.9 times higher clock frequency and have 17.3% more gates on average.