A Synchronous 50% Duty-Cycle Clock Generator in 0.35- $\mu$ m CMOS

This paper presents a synchronous 50% duty-cycle clock generator (DCCG). The proposed DCCG circuit comprises of a clock generator and a phase error integrator. The clock generator is edge-triggered by an input signal to produce an output whose pulse width is determined by a delay line. The delay line is controlled by the phase error integrator which detects the phase difference between the input and output signals. The proposed DCCG is designed such that when the phase error is zeroed, i.e., the input and output signals are synchronized, the delay is properly adjusted and the output signal duty cycle converges to 50%. The proposed DCCG is implemented in a 0.35-μm CMOS process. The circuit can operate from 70 to 500 MHz, and accommodates a wide range of input duty cycle ranging from 5% to 95%. The duty-cycle error of the output signal is less than 1.5%. Operated from a 3.3-V supply voltage, this circuit dissipates 7 mA at 500 MHz.