A 2.4 GHz fractional-N PLL with a low-power true single-phase clock prescaler

Abstract

A 2.4 GHz fractional-N PLL implemented in 65-nm CMOS process is presented in this letter. A TSPC dual-modulus prescaler is proposed to reduce the PLL’s power consumption by merging one of the branches of the true single-phase clocked (TSPC) D flip-flops. The measured synthesizer output frequency ranges from 2.16 to 2.7GHz, and consumes 8 mW from a 1.3 V power supply. The in-band phase noise is -98 dBc/Hz at 100 kHz offset, and -115 dBc/Hz at 1 MHz offset at a carrier frequency of 2.438 GHz. The circuit achieves the RMS jitter of 0.86 ps and figure of merit of -230 dB, with the fractional spurs below -55 dBc.