Outline Abstract Conventional flip-flops Proposed flip-flop design Simulation conditions and test bench Simulation results Conclusion
Abstract This paper describes the Differential Pass Transistor Pulsed Latch (DPTPL) which enhances D-Q delay and reduces power consumption using NMOS pass transistors and feedback PMOS transistors. The power consumption of the proposed pulsed latch is reduced significantly due to the reduced clock load and smaller total transistor width compared to conventional differential flip-flops. The simulations were performed in a 0.13 um CMOS technology at 1.2V supply voltage with 1.25GHz clock frequency.
In a recent high frequency microprocessor, the clocking system consumed 70% of the total chip power consumption. In the clocking system, 90% of the power is consumed by the flip-flops.
Conventional flip-flops The Master-Slave Latch (MSL) is a good candidate for low power applications. Hybrid latch flip-flop (HLFF) and semi-dynamic flip-flop (SDFF) have small delay at the cost of power consumption. Sense amplifier-based flip-flops (SAFF) and modified sense amplifier-based flip-flops (MSAFF) as well as differential type flip-flops. The ep-SFF has the advantages of lower power consumption and small delay. The modified SDFF (MSDFF) is one of the fastest flip- flops.
Schematics of (a) explicit-pulsed hybrid static flip-flop, (b) pulsed-clock generator, and (c) pulsed generator timing diagram
Proposed flip-flop design Schematics of (a) differential pass transistor pulsed latch (DPTPL) and (b) pulsed clock generator
Simulation conditions and test bench First, all flip-flops are simulated in a 0.13 um CMOS technology at 100 ◦ C with 1.2V supply voltage and normal process corners. The operating clock frequency in this simulation is 1.25GHz. For fair comparison of simulation results, all of the flip- flops are optimized to have minimum E×D with the same output load of 25fF. Secondly, for chip testing, Operating frequency in this simulation is 1GHz.
Power and delay measurement test bench for overall comparison On-chip delay measurement block diagram
Layout of overall block diagram for chip test
Simulation results Signal waveforms of DPTPL
Delay comparison: conventional versus proposed flip-flops
Overall power comparison
Conclusion DPTPL, utilizing the strong drivability of NMOS with positive feedback PMOS transistors, enables faster operation than their conventional counterparts. It also has an advantage of lower power consumption mainly due to simplicity and smaller clock load, and total gate width. DPTPL reduces E × D by 45.5% over ep-SFF, which have the best characteristics in our simulations among the conventional flip-flops.