Semi-parallel rank-order filtering in analog VLSI

This paper presents an implementation of semi-parallel rank-order filtering in analog VLSI to collect position-encoded rank data. The rank competition is based on voltage inputs and a popular winner-take-all(WTA) circuit. The input competition is performed in parallel and each rank is determined serially. Negative feedback ensures that neither the previous winner nor its nearest neighbors will compete in the new rank competition. This circuit is compact (21 transistors per input element), and can serve unlimited number of input elements. The 20 element array that we have fabricated and tested consumes approximately 0.2 mW of power, has good resolution (2 mV between inputs) and good response time (0.05 ms) in subthreshold operation.