Toshiba with energy-saving Flip-Flop Circuit

Measured data verifies that the power dissipation of the new flip-flop is up to 77% less than that of a typical conventional flip-flop and that it achieves a 24% reduction in total power consumption when applied to a wireless LAN chip. A typical flip-flop incorporates a clock buffer to produce a clock inverted signal required for the circuit’s operation. When triggered by a signal from the clock, the clock buffer consumes power, even when the data is unchanged. In order to reduce this power dissipation, a power-saving design technique called clock gating is widely used to cut delivery of the clock signal to unused blocks. However, after applying the clock gating, the flip-flop active rate, a measure of data change rate per clock, is only 5-15%, indicating that there is still plenty of room for further power reduction. In order to save power, Toshiba changed the structure of the typical flip-flop and eliminated the power-consuming clock buffer. This approach brings with it the problem of data collision between the data writing circuitry and the state holding circuitry in the flip-flop, which Toshiba overcame by adding adaptive coupling circuitry to the flip-flop. A combination of an nMOS transistor and a pMOS ransistor, this circuitry adaptively weakens state-retention coupling and prevents collisions. Despite the addition of the adaptive coupling circuitry, overall simplification of the basic flip-flop configuration reduces the transistor count from 24 to 22, and the cell area is less than that of the conventional flip-flop.