Patent ID: 8937828
Filing Date: 2015-01-20
Classification: G11C

Abstract:
1. An associative memory, comprising: a reference data storage cell circuit that stores R reference data pieces each having a W bit length, R being an integer not less than 2, W being an integer not less than 2; a comparator circuit that compares search data to be searched for and having a W bit length to each of said R reference data pieces on a bit basis and outputs R distance signals each representing a distance between said search data and said reference data and having bit values for W bits as a comparison result between said search data and said R reference data; R conversion circuits provided corresponding to said R distance signals and each having an oscillation circuit including k delay circuits connected in a ring shape, k being an integer that satisfies W/N or (W/N)+1, N being an integer not less than 3; R selection circuits provided corresponding to said R distance signals and said R conversion circuits and each including k path selection circuits; and a detecting circuit that detects an earliest changing output signal among R output signals output from said R conversion circuits and outputs the detected signal as a signal representing the most similar reference data to said search data, wherein said R selection circuits each produce k selection signals used to select one delay path from N+1 delay paths in each of said k delay circuits based on said corresponding W-bit distance signal so that delay time in said k delay circuits is shorter as a distance represented by a corresponding W-bit distance signal is smaller and delay time in said k delay circuits is longer as the distance represented by said corresponding W-bit distance signal is greater and outputs the produced k selection signals to said corresponding conversion circuit, and upon receiving said k selection signals from said corresponding selection circuit, said R conversion circuits each oscillate through k delay paths selected by the received k selection signals and outputs the oscillated oscillation signals as an output signal to said detection circuit.