A Low Phase Noise Open Loop Fractional-N Frequency Synthesizer With Injection Locking Digital Phase Modulator

This brief presents a two stage open loop fractional-N frequency synthesizer using proposed injection locking phase modulator for low power applications. A novel low power injection locking oscillator (ILO)-based digital phase modulator (DPM) is proposed in this brief. The maximum differential nonlinearity (DNL) of proposed DPM is smaller than 0.3 degree in the whole range with 1.6 mW power consumption. An integer-N injection locking phase locked loop (ILPLL) is designed to generate the radio frequency signals for the second stage open loop frequency synthesizer. With an injection strength adjustment unit, the open loop fractional-N frequency synthesizer employing proposed DPM achieved excellent in band phase noise and instantaneous frequency switching with low power consumption. This frequency synthesizer is fabricated on 28-nm CMOS technology and its active area is 0.08 mm
²
. The output frequency range is from 320 MHz to 520 MHz and the power dissipation is 2.7 mW from 0.9 V supply in fractional-N mode. The measured RMS jitter integrated phase noise from 10 KHz to 40 MHz of 440 MHz and 440.4 MHz carrier frequency are 3.8 ps and 17.6 ps, respectively. The corresponding figure of merits (FoM) are -231 dB and -211 dB, respectively.