26TSPC: A Low Hold Time, Low Power Flip-Flop With Clock Path Optimization

Recent low-power flip-flops (FFs) synthesize a signal
$(\boldsymbol{CKN})$
that is activated only when the input data
$(\boldsymbol{D})$
updates the output state
$(\boldsymbol{Q})$
. It saves power consumption by avoiding unnecessary transitions in internal nodes. However, the circuit for
$\boldsymbol{CKN}$
that removes all redundant transitions becomes complex. As a result, its delay worsens timing parameters (setup time, hold time,
$\boldsymbol{CK}\_\boldsymbol{Q}$
delay) and the robustness of FFs too. By optimizing the delay of the clock insertion paths, the presented flip-flop (26TSPC) maximizes efficiency without speed degradation, while maintaining low hold time. Its design is based on 18TSPC, one of the fast and energy-efficient FFs, and its contention and redundant transition issues are also resolved. Post-layout simulation results based on 65 nm CMOS process show that 26TSPC consumes 83.9%/71.4% less power than that of conventional transmission-gate flop-flop (TGFF) with 10%/20% activity ratio at 1V and 75.4%/65.3% less power than that of TGFF with 10%/20% activity at 0.4V respectively. In addition, the hold time of 26TSPC is negative in all corners, featuring better timing reliability than other low-power FFs.