Pulsewidth Control Loop as a Duty Cycle Corrector

Abstract

The clock distribution and generation circuitry forms a critical component of current synchronous digital systems. A digital system’s clocks must have not only low jitter, low skew, but also well-controlled duty cycle in order to facilitate versatile clocking techniques. In high-speed CMOS clock buffer design, the duty cycle of a clock is liable to be changed when the clock passes through a multistage buffer because the circuit is not pure digital [8]. In this paper, we propose a pulsewidth control loop referred as MPWCL (modified pulsewidth control loop) that adopts the same architecture as the conventional PWCL, but with a new pulse generator and new charge pump circuit as a constituent of the duty cycle detector. Thanks to using new building blocks the proposed pulsewidth control loop can control the duty cycle in a wide range, and what is more important it becomes operative in saturation region too, what provides conditional for fast locking time. For 1.2 µm double-metal double-poly CMOS process with Vdd = 5 V and operating frequency of 133 MHz, results of SPICE simulation show that the duty cycle can be well controlled in the range from 20 % up to 80 % if the loop parameters are properly chosen.