Dram direct sensing scheme

Abstract

A direct sensing circuit and method for reading data from a memory cell connected to a bitline, with open bitline sensing without using a reference bitline signal, onto a data line in a data read operation. Prior to the data read operation, both the bitline and the data line are precharged to precharge voltages and a sense node is precharged to ground. A pFET device has its gate coupled to a signal developed on the bitline from the memory cell to detect and amplify the signal level thereof, and has its source coupled to a voltage source and its drain coupled to a sense node, such that the signal developed on the bitline determines the degree of turn-on of the pFET device. An nFET device has its gate coupled to the sense node to detect and amplify the signal level thereof, and has its drain coupled to the data line. When sensing a low data signal, the signal developed on the bitline causes subthreshold voltage leakage current through the pFET device to charge the gate of the nFET device which is floating to amplify the signal developed on the bitline to pull down the precharged data line. When sensing a high data signal, the pFET device and the nFET device remain inactivated, and the data line remains at its precharge high voltage. An nFET writeback device is coupled between the data line and the bitline which is switched on to begin a data writeback into the memory cell when the signal develops on the data line.