Automated reference cell trimming verify

摘要

A reference trimming verify circuit and method is provided for performing a program verify operation on a reference cell transistor in an array of Flash EEPROM memory cells. A reference current branch is used to generate a reference current corresponding to a predetermined overdrive voltage of the reference cell to be programmed. A drain current branch is coupled to the reference cell transistor to be programmed and generates a drain current at a fixed gate voltage applied to its control gate and at a predetermined drain voltage applied to its drain when the drain current is at the desired level. A comparator is used to compare a sensed voltage corresponding to the drain current and a reference voltage corresponding to the reference current. The comparator generates an output signal which is at a low logic level when the sensed voltage is less than the reference voltage and which is at a high logic level when the sensed voltage is greater than the reference voltage. A program pulse is applied to the reference transistor each time the comparator generates the low logic level and terminates the program pulse when the comparator generates the high logic level.