A 2.1-to-2.8-GHz low-phase-noise all-digital frequency synthesizer with a time-windowed time-to-digital converter

A 2.1-to-2.8-GHz low-power consumption all-digital phase locked loop (ADPLL) with a time-windowed time-to-digital converter (TDC) is presented. The time-windowed TDC uses a two-step structure with an inverter- and a Vernier-delay time-quantizer to improve time resolution, which results in low phase noise. Time-windowed operation is implemented in the TDC, in which a single-shot pulse-based operation is used for low power consumption. The test chip implemented in 90-nm CMOS technology exhibits in-band phase noise of -105 dBc Hz, where the loop-bandwidth is set to 500 kHz with a 40-MHz reference signal, and out-band noise of -115 dBc Hz at a 1-MHz offset frequency. The chip core occupies 0.37 mm² and the measured power consumption is 8.1 mA from a 1.2-V power supply.