US Patent 7391235 - Mem-resistor crossbar signal processor
There has been some interest recently in "memristors" which have been noted as representing a fourth fundamental circuit component after resistors, capacitors, and inductors. While the recent interest stems from the discovery by Hewlett-Packard researchers of bilayer oxides as a new type of memristor material for their nanoscale crossbar arrays a variety of other materials including chalcogenides, perovskites, and semiconducting polymers have been used over the past several decades having similar memory resistance properties and which form the basis of several proposals for RRAM being pursued by a variety of companies including Micron Technologies, Samsung, and Unity Semiconductor. While most proposed applications of memristor type material have been in non-volatile memory this patent teaches a variety of circuit configurations in which programmable resistances in a crossbar array are used in combination with operational amplifier circuitry for signal processing applications such as waveform generation, programmable filters, communication switching, and pattern analysis. Claim 1 reads:
1. A device comprising:
a crossbar array including a programmable impedance layer and having crosspoint impedances Zij;
an array of input impedances Zin(i) electrically connected to input columns of the crossbar array; and
an array of op-amps electrically connected to outputs rows of the crossbar array wherein each of the op-amps include a feedback impedance Zout(j) connected between an output terminal and an inverting input of the op-amp, wherein the crossbar array, the array of input impedances, and the array of op-amps are configured to produce a matrix transformation T(i,j), based on the impedances Zin(i), Zij, and Zout(j), for combining input signals.