Electrically erasable programmable read-only memory array

Abstract

A memory (1) operative in an erase mode, a program mode, or a read mode includes a memory cell array, word lines (30, 40, 50, 60), a row decoder (9) connected to the word lines, bit lines (2, 4, 6, 8), a precharge circuit (70, 72, 74, 76, 78, 80) connected to the bit lines, a load circuit (22, 23, 24, 25, 26, 27, 28, 29) connected to the bit lines, and a sense circuit (12, 14, 16, 18) connected to the bit lines. The memory array includes both floating gate MOSFET transistors and switch MOSFET transistors arranged in groups associated with respective subsets of word lines and bit lines. Within each group, the sources of the floating gate transistors (32, 34, 42, 44) and switch transistors (35, 45) are commonly connected, the control gates and drains of the floating gate transistors are respectively connected to a unique associated word line (30, 40)--associated bit line (2, 4) pair, and each of the switch transistors has its gate connected to a unique associated word line and its drain connected to a reference line (5). The sense current threshold is set between an amount of current drawn by one ON floating gate transistor and an amount of current drawn by a number of OFF floating gate transistors equal to the number of floating gate transistors within a group connected to a single bit line, minus one.