Self-retention of data in power-gated circuits

Data retention is important to avoid data loss in power-gated circuits. Isolation circuitry should be used to keep output value as well as to avoid floating; a flip-flop capable of data retention, called retention flip-flop, should be used to keep flip-flop state. Examples of their implementations are reviewed. Due to extra circuitry and wires they introduce, it is important to understand how much increase of area and wirelength should be tolerated to support data retention, which we quantitatively analyze using several example circuits in 65-nm technology. A self-retention mechanism is proposed to alleviate the increase; it relies on the potential change of virtual power rail to detect the time for data retention and data restore thereby removing control signal implemented as extra wires and buffers in conventional power-gated circuits. Experiments show 8.6% decrease of wires on average.