Level-Converting Retention Flip-Flop for Reducing Standby Power in ZigBee SoCs

In this paper, we propose a level-converting retention flip-flop (RFF) for ZigBee systems-on-chips (SoCs). The proposed RFF allows the voltage regulator that generates the core supply voltage (VDD,core) to be turned off in the standby mode, and it thus reduces the standby power of the ZigBee SoCs. The logic states are retained in a slave latch composed of thick-oxide transistors using an I/O supply voltage (VDD,IO) that is always turned on. Level-up conversion from VDD,core to VDD,IO is achieved by an embedded nMOS pass-transistor level-conversion scheme that uses a low-only signal-transmitting technique. By embedding a retention latch and level-up converter into the data-to-output path of the proposed RFF, the RFF resolves the problems of the static RAM-based RFF, such as large dc current and low readability caused by threshold drop. The proposed RFF does not also require additional control signals for power mode transitioning. Using 0.13-μm process technology, we implemented an RFF with VDD,core and VDD,IO of 1.2 and 2.5 V, respectively. The maximum operating frequency is 300 MHz. The active energy of the RFF is 191.70 fJ, and its standby power is 350.25 pW.