A compact transformer-based fractional-N ADPLL in 10-nm FinFET CMOS

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Abstract

In this article, we introduce a fractional-N all-digital phase-locked loop (ADPLL) architecture based on a single LC-tank, featuring an ultra-wide tuning range (TR) and optimized for ultra-low area in 10-nm FinFET CMOS. Underpinned by excellent switches in the FinFET technology, a high turn-on/off capacitance ratio of LC-tank switched capacitors, in addition to an adjustable magnetic coupling technique, yields almost an octave TR from 10.8 to 19.3GHz. A new method to compensate for the tracking-bank resolution can maintain its quantization noise level over this wide TR. A new scheme is adopted to overcome the metastability resolution problem in a fractional-N ADPLL operation. A low-complexity TDC gain estimator reduces the digital core area by progressive averaging and time-division multiplexing. Among the published fractional-N PLLs with an area smaller than 0.1mm2, this work achieves an rms jitter of 725fs in an internal fractional-N mode of ADPLL's phase detector (2.7-4.825GHz) yielding the best overall jitter figure-of-merit (FOM) of -232dB. This topology features small area (0.034mm2), wide TR (56.5%) and good supply noise rejection (1.8%/V), resulting in FOMs with normalized TR (FOMT) of -247dB, and normalized TR and area (FOMTA) of -262dB.

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APA

Li, C. C., Yuan, M. S., Liao, C. C., Chang, C. H., Lin, Y. T., Tsai, T. H., … Staszewski, R. B. (2021). A compact transformer-based fractional-N ADPLL in 10-nm FinFET CMOS. IEEE Transactions on Circuits and Systems I: Regular Papers, 68(5), 1881–1891. https://doi.org/10.1109/TCSI.2021.3059484

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