Abstract: A 0.20–2.43 GHz fractional-N frequency synthesizer is presented for multi-band wireless communication systems, in which the scheme adopts low phase noise voltage-controlled oscillators (VCOs) and a charge pump (CP) with reduced current mismatch. VCOs that determine the out-band phase noise of a phase-locked loop (PLL) based frequency synthesizer are optimized using an automatic amplitude control technique and a high-quality factor figure-8-shaped inductor. A CP with a mismatch suppression architecture is proposed to improve the current match of the CP and reduce the PLL phase errors. Theoretical analysis is presented to investigate the influence of the current mismatch on the output performance of PLLs. Fabricated in a TSMC 0.18-µm CMOS process, the prototype operates from 0.20 to 2.43 GHz. The PLL synthesizer achieves an in-band phase noise of −96.8 dBc/Hz and an out-band phase noise of −122.8 dBc/Hz at the 2.43-GHz carrier. The root-mean-square jitter is 1.2 ps under the worst case, and the measured reference spurs are less than −65.3 dBc. The current consumption is 15.2 mA and the die occupies 850 µm×920 µm.

Key words: Frequency synthesizer, Charge pump (CP), Voltage-controlled oscillator (VCO), Current mismatch, Phase noise

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