Phase change memory with flexible time-based cell decoding

摘要

Methods and systems for time-based cell decoding for PCM memory. Generally, the higher the PCM element resistance, the longer it takes for a read output to change state. PCM memory output is determined using differentiated timings of read outputs changing state, rather than differentiated values of read outputs. In some single-bit single-ended sensing embodiments, a reference, with resistance between the resistances corresponding to a pair of adjacent logical states, is stored in multiple reference cells; a “vote” unit emits a clock signal when a majority of the reference cell read outputs transition at the vote unit. Timing units produce different binary outputs depending on whether a data read output or the clock signal changes state first at the timing unit. Time-based decoding provides advantages including improved temperature and drift resilience, improved state discrimination, improved reliability of multibit PCM, and fast and reliable sensing.

主权项

1. A memory, comprising:
multiple groups of phase change memory cells, ones of said groups comprising multiple phase change memory storage cells and multiple phase change memory reference cells storing one or more references, and configured such that said storage cells and said reference cells in ones of said groups are read together; multiple sense amplifiers, ones of said sense amplifiers configured to sense read outputs of corresponding ones of said storage cells and said reference cells when one of said groups is read, and to produce sense amplifier output transitions at times at least partially dependent on the states stored by said corresponding storage cells and reference cells; and multiple output units, ones of said output units configured to output a different binary value depending on whether a reference signal generated in at least partial dependence on one or more of said sense amplifier outputs corresponding to one of said references, or one of said sense amplifier outputs corresponding to one of said storage cells, first change state at said output unit.