Abstract
Winner-Take-All (WTA) circuits play an important role in applications where a single element must be selected according to its relevance. They have been successfully applied in neural networks and vision sensors. These applications usually require a large number of inputs for the WTA circuit, especially for vision applications where thousands to millions of pixels may compete to be selected. WTA circuits usually exhibit poor response-time scaling with the number of competitors, and most of the current WTA implementations are designed to work with less than 100 inputs. Another problem related to the large number of inputs is the difficulty to select just one winner, since many competitors may have differences below the WTA resolution. In this paper, a WTA circuit is presented that handles more than four thousand inputs, to our best knowledge the hitherto largest WTA, with response times below the microsecond, and with a guaranty of just a single winner selection. This performance is obtained by the combination of a standard analog WTA circuit and a fast digital single-winner selector with almost no size penalty. This WTA circuit has been successfully employed in the fabrication of a Selective Change-Driven Vision Sensor based on 180 nm CMOS technology. Both simulated and experimental results are presented in the paper, showing that a single pixel event can be selected in just 560 ns, and a multipixel pixel event can be processed in 100 μs. Similar results with a conventional approach would require a camera working at more than 1 Mfps for the single-pixel event detection, and 10 kfps for the whole multipixel event to be processed.
Highlights
The selection of the most relevant data is a key process in many computational strategies based on data-driven execution
Both simulated and experimental results are presented in the paper, showing that a single pixel event can be selected in just 560 ns, and a multipixel pixel event can be processed in 100 μs
The simulations and experiments performed with the WTA circuit showed good resolution for choosing a winner, and a delay of less than 1 μs, which is beyond the actual capacity of the Selective Change Driven Vision (SCD) sensor
Summary
The selection of the most relevant data is a key process in many computational strategies based on data-driven execution. The simplicity and power of the WTA concept allows the implementation of WTA-based circuits in high-performance analog electronic applications involving competing processes, such as bioinspired (neuromorphic) vision sensors [2,3]. In this new paradigm of vision sensors, images are not managed as frames, but as events, requiring specific electronic circuitry to process, in real time, this nonconventional representation of pixels. The (single/hard) WTA circuit included in these SCD sensors is key in order to select the best pixel to read at any instant
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