A wideband 2.4-GHz delta-sigma fractional-N PLL with 1-MB/s in-loop modulation

A phase noise cancellation technique and a charge pump linearization technique, both of which are insensitive to component errors, are presented and demonstrated as enabling components in a wideband CMOS delta-sigma fractional-N phase-locked loop (PLL). The PLL has a loop bandwidth of 460 kHz and is capable of 1-Mb/s in-loop FSK modulation at center frequencies of 2402 + k MHz for k = 0, 1, 2,..., 78. For each frequency, measured results indicate that the peak spot phase noise reduction achieved by the phase noise cancellation technique is 16 dB or better, and the minimum suppression of fractional spurious tones achieved by the charge pump linearization technique is 8 dB or better. With both techniques enabled, the PLL achieves a worst-case phase noise of - 121 dBc/Hz at 3-MHz offsets, and a worst-case in-band noise floor of -96 dBc/Hz. The PLL circuitry consumes 34.4 mA from 1.8-2.2-V supplies. The IC is realized in a 0.18-mum mixed-signal CMOS process, and has a die size of 2.72 mm x 2.47 mm.