Proposal for Memristors in Signal Processing

Recently researchers at Hewlett-Packard have announced the discovery of a new material having resistance switching characteristics and which has been characterized as a fourth fundamental circuit component called the “memristor”[1]. It is proposed to combine such memristors with operational amplifier circuitry and fixed resistor elements so as to form a programmable signal processor capable of selective transmission and multiplexing of multiple signals for applications in communications and programmable drive waveform control. Description of Device While the recent revelation by Hewlett-Packard of bi-layer titanium oxide as a candidate material for the “missing memristor” initially speculated by Leon Chua [2] is an interesting and important development, it is not entirely unprecedented. Similar resistance variability effects in thin film oxides have been studied using perovskite [3] and similar materials. However, this research has mostly been limited to applications in non-volatile memory in which the switching resistance acts to store binary data in the form of high or low resistance states. Such materials may also have use in signal processing and control applications. Fig. 1 illustrates an idealized approximation for the behavior of memristance material in which an applied voltage greater than some positive threshold voltage VL1 initiates a memristance region exhibiting variation from a high resistance level RH to a low resistance level RL as voltage is increased. Similarly, resistance may be converted from a low level back to a high level by a reversed polarity voltage in the region between -VL2 and –VH2. In the small signal region between –VL2 and VL1 the material is either at a high or low resistance level depending on the history of voltage application to the material. Fig. 2 illustrates an array of memristors M1-M4 having inputs connected to fixed resistors R1-R4 and outputs connected to a common inverting input of an operational amplifier having a feedback resistance RF. Operational amplifiers in such a configuration exhibit the well known effect of summing the input signals based on a weighting determined by a ratio of the feedback resistance and the input resistances. However, the inclusion of memristors allows controllability in selecting which signals to sum and, if tuned within the memristance region, the weighting values of each input signal may also be adjusted. By using harmonic sinusoidal signals or step