Flip-Flops for Accurate Multiphase Clocking: Transmission Gate Versus Current Mode Logic

Dynamic transmission gate (DTG) flip-flops (FFs) (DTG-FFs) and current mode logic (CML) FFs (CML-FFs) are compared targeting power efficient multiphase clock generation with low phase error. The effect of component mismatches on multiphase clock timing inaccuracies is modeled and compared, using the product of mismatch-induced jitter variance and power consumption as a figure-of-merit (FOM). Analytical equations are derived to estimate the jitter-power FOM for DTG-FF- and CML-FF-based dividers. Simulations confirm the trends predicted by the equations and show that DTG-FFs achieve a better FOM than CML-FFs. The advantage increases for CMOS processes with smaller feature size and for a lower input frequency compared to fT.