US Patent 9355739 Bitline circuits for embedded charge trap multi-time-programmable-read-only-memory

A bitline circuit for embedded Multi-Time-Read-Only-Memory including a plurality of NMOS memory cells coupled to a plurality of wordlines in each row, bitlines in each column, and a source-line. More specifically, the bitline circuit controls a charge trap behavior of the target NMOS memory array by mode-dependent bitline pull-down circuit, thereby discharging the bitline strongly to GND to trap the charge effectively in a Programming mode, and discharge the bitline weakly to GND to develop a bitline voltage to detect the charge trap state. The mode dependent circuit is realized by using at least two NMOS to switch the device strength, using a pulsed gate control in a Read mode, or using analog voltage to limit the bitline current. The proposed method further includes a protection device, allowing all bitline control circuit using thin oxide devices. The bitline circuits having mode and bank access dependent bitline circuit further enables a single device memory array, by using two arrays, wherein said one of the array is used for reference to the other array using an open bitline architecture.