A Fast-Locking, Low-Jitter Pulsewidth Control Loop for High-Speed ADC

A fast-locking, high-precision, and low-jitter pulsewidth control loop (PWCL) for high-speed high-resolution analog-to-digital converter is presented. Only through controlling the delay of rising edge to adjust duty cycle, the clock jitter could be suppressed greatly. An improved charge pump with a follower circuit and self-biased loop was designed to decrease the voltage ripples for higher accuracy and lower jitter. A startup circuit was adopted to enable the pulsewidth control loop lock rapidly. With the SMIC 0.18 μm 3.3 V CMOS process, the simulation and measured results show that within 180 ns the PWCL can lock the clock duty cycles for the accuracy of 50±1% with 10%~90% input duty cycle from 50 to 550 MHz. The rms-jitter is 73 fs at 250 MHz. The active area is about 0.023 mm².