DLL-based 4-phase duty-cycle and phase correction circuit for high frequency clock tree

Abstract

In high-speed data transmission applications such as double data rate memory and double sampling ADCs, clock generation and distribution circuits must provide the clocks with precise duty cycle of 50% and sufficient timing margin. The proposed DLL-based 4-phase duty-cycle and phase correction circuit, consisting of delay-locked loop (DLL) and 45 phase clock generator (SR latch) corrects distorted duty-cycle clock to 50% duty-cycle. The distorted duty-cycle input clock passes through the DLL. After the DLL is locked, the delay of delay line is identical to the period of input clock. Lastly, 4-phase, 50% duty-cycle clocks is generated from the combination of rising edges of signals at each 1/4 points of delay line. The proposed circuit is implemented in 65nm CMOS. The simulation results shows that the frequency range of the proposed circuits is 550-1600MHz, the maximum duty cycle error of the output clock can be less than 1% with the input duty cycle correction ranging from 25% to 80%. The phase difference with the 4-phase output clock is 250±3ps at a frequency of 1GHz. The measured power dissipation is 4.3mW.