Clock Jitter Reduction and Flat Frequency Generation in PLL Using Autogenerated Control Feedback

Abstract

In this paper, a method has been proposed by which one can reduce the clock jitter and achieve almost flat frequency clock output from the phase-locked loop (PLL), independent of the power supply voltage fluctuation. These voltage fluctuations occur when a given chip comes out from the sleep mode to the active mode. This causes the chip to draw a hasty current, which in turn produces LdI/dt noise. That causes the voltage to drop and also to oscillate at the power delivery network’s resonance frequency. This power supply noise causes clock jitter. The voltage-controlled oscillator of the proposed PLL is designed at 45-nm technology such that when there is supply voltage variation, it is automatically corrected by a feedback methodology having only 11-ps response time delay, compared to 588-ps clock period. Simulation result shows that, for the proposed new PLL design, the number of places where the clock periods are altered due to this power supply voltage fluctuation is reduced. The performance of the proposed PLL design in terms of reduction of clock jitter, caused by the variation of power supply voltage and the flatness of the frequency versus power supply voltages, is tested by feeding the clock to a circuit (c17 of ISCAS’85) for the conventional methodology and also for our new methodology. It has been shown that, using the proposed method, the clock jitter caused by the power supply noise can be reduced by about 50% compared to the conventional design methodology.