Memory cell capable of storing more than two logic states by using

Abstract

A system and process which enables storage of more than two logic states in a memory cell. In one embodiment, a programmable resistor is coupled in series with a transistor between a supply voltage and a data read line. When an access signal is asserted, the transistor provides a conductive path, and a voltage drop is sustained by the programmable resistor. The programmable resistor has a resistance which is set during a programming step to one of a plurality of values by passing a heating current through the programmable resistor for one of a corresponding plurality of predetermined lengths of time. When the access signal is asserted, the voltage drop sustained across the programmable resistor is indicative of the stored logic state. An analog-to-digital (A/D) converter is coupled to the data read line so as to sense the voltage drop and determine the state represented. Since the additional logic states may be used to represent additional information bits, this memory circuit increases the number of bits that may be stored per memory cell, thereby increasing the storage density and reducing the cost per bit.