Nonvolatile semiconductor memory device

Abstract

To read data stored on a memory cell transistor with a floating gate, a flash memory uses: a single-gate reference transistor; a differential sense amplifier; and a gate voltage generator for generating a gate voltage for the reference transistor. The gate voltage generator includes: a dummy cell transistor, which has the same structure as the memory cell transistor and has been turned ON; a current mirror for creating a current proportional to a drain current of the dummy cell transistor; an NMOS transistor for generating a gate voltage for the reference transistor in accordance with the current created by the current mirror; and a voltage hold circuit for holding the gate voltage generated. Even if temperature or fabricating process conditions have changed, this construction ensures accurate and high-speed read operation.