Comparative Study of Gain Cells for Pseudo-SRAM

Comparative study on 2T, 3T, and 4T gain cells for pseudo-SRAM is demonstrated. Data retention time (DRT) and leakage power performances of these optimally-designed cells are systematically analyzed. The 2T cell having a minimally suppressed cell area suffers from its short DRT. The 3T cell, which is free from the READ disturb-mechanism through the help of the isolated read port (IRP), also has a short DRT comparable to the 2T cell. Although the DRTs of these cells can be successfully extended by introducing a retention bias control, a rise in temperature could severely degrade these DRTs. In contrast, the 4T cell with the internal feedback structure enables it to prolong the DRT. The feedback effect is also of advantage for developing strong tolerance to temperature- and process-variations. The retention-bias control technique can effectively reduce the standby power for all the cells.