Bit line reference circuits for binary and multiple-bit-per-cell memories

Abstract

Auto-tracking bit line reference schemes generate a “½ cell current” reference by programming reference cells to threshold voltages that are between threshold voltage levels used to represent data. A common word line can control both a selected memory cell and a reference cell to provide a reference current, and differential sense amplifiers can compare a bit line current to reference currents to thereby distinguish data values. Current through other reference cells can be mirrored to pull-up devices to further improve the tracking of the reference line and bit line currents. Embodiments of the invention can be used with binary and multiple-bit-per-cell memories and with a variety of memory array architectures and memory cell structures.