Auto-tracking bit line reference schemes generate a " 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.
