A precharged-capacitor-assisted sensing (PCAS) scheme with novel level controllers for low-power DRAMs

A precharged capacitor-assisted sensing (PCAS) scheme suitable for low-power DRAM using boosted-sense ground (BSG) is proposed. In this scheme, the data on bitlines are sensed with the assistance of precharged capacitors. Precise data level generation is achieved with sense speed 4.2 ns faster than the conventional scheme in the case that bitline swing is 1.4 V. Necessary decoupling capacitors can be efficiently implemented in memory arrays by using junction capacitors between well and substrate so that the area penalty of decoupling capacitors can be minimized. To keep sensed data stable, two types of level controllers are introduced. A voltage downconverter (VDC) with a current mirror discharger (CMD) compensates for the change of both data levels during write/read operations. A level controller with charge transfer amplifier (CTA) prevents the BSG level from falling during the row active period. The two level controllers greatly improve data-retention characteristics.