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A 3.5 GHz Wideband ADPLL With Fractional Spur Suppression Through TDC Dithering and Feedforward Compensation

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5 Author(s)
Temporiti, E. ; STMicroelectronics-Studio di Microelettronica, Pavia, Italy ; Weltin-Wu, C. ; Baldi, D. ; Cusmai, M.
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Nonlinearities in the time-to-digital converter (TDC) are a significant source of fractional spurs in a divider-less fractional-N ADPLL. Using an abstract model for the TDC, this paper presents a dithering method which is mathematically shown to suppress fractional tones, in conjunction with a feedforward dither cancellation technique which suppresses dither-induced phase noise. A mostly-digital calibration algorithm is also presented which ensures consistent phase noise cancellation across PVT conditions. The aforementioned techniques are implemented in a 65 nm digital CMOS prototype running at 3.5 GHz from a 35 MHz reference. The ADPLL demonstrates - 101 dBc/Hz in-band phase noise at a bandwidth of 3.4 MHz, - 58 dBc worst fractional spurious performance across the entire fractional range, and consumes 8.7 mW from a 1.2 V supply.

Published in:

Solid-State Circuits, IEEE Journal of  (Volume:45 ,  Issue: 12 )