A 1.35-V 16-Mb Twin-Bit-Cell Virtual-Ground-Architecture Embedded Flash Memory With a Sensing Current Protection Technique

In this paper, a 1.35 V 16 Mb twin-bit-cell virtual ground architecture embedded Flash memory is presented. To reduce the sensing margin loss caused by the side-leakage current in the virtual ground architecture memory array, a sensing current protection technique has been proposed. A reference voltage generating circuit for dynamic sensing window tracking is designed to maximize the sensing window under various PVT (Process-Voltage-Temperature) conditions. With the reference voltage generating circuit and a high performance sense amplifier, high speed read operation is achieved. As four bitlines have to be selected to read one bit, an S-D-P-P (Source-Drain-Protection-Protection) style column decoding methodology has been introduced to support the sensing current protection technique. The embedded Flash IP has been fabricated in a GSMC 90 nm 4 poly 4 metal CMOS process. The die size of the proposed Flash IP is 3.2 mm² and the memory cell size is 0.16 μm². Access time of 36 ns at 1.35 V has been achieved.