A Fractional-N Digitally Intensive PLL Achieving 428-fs Jitter and <-54-dBc Spurs Under 50-mV pp Supply Ripple

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Abstract

In this article, we present a 4.5-5.1-GHz fractional-N digitally intensive phase-locked loop (DPLL) capable of maintaining its performance in face of a large supply ripple, thus enabling a direct connection to a switched-mode dc-dc converter. Supply pushing of its inductor-capacitor (LC) oscillator is suppressed by properly replicating the supply ripple onto the gate of its tail current transistor, while the optimum replication gain is determined by a new on-chip calibration loop tolerant of supply variations. A proposed configuration of cascading a supply-insensitive slope generator with an output of a current digital-to-analog converter (DAC) linearly converts the phase error timing into a corresponding voltage, which is then quantized by a successive approximation register (SAR) analog-to-digital converter (ADC) to generate a digital phase error. We also introduce a low-power ripple pattern estimation and cancellation algorithm to remove the phase error component due to the supply-induced delay variations of loop components. Implemented in 40-nm CMOS, the DPLL prototype achieves the performance of 428-fs rms jitter, &lt;-55-dBc fractional spur, and &lt;-54-dBc maximum spur while consuming 3.25 mW and being subjugated to a sinusoidal or sawtooth supply ripple of 50 mV <formula> <tex>$_{pp}$</tex> </formula> at 50-MHz reference divided by 3, 6, or 12.

Original languageEnglish
JournalIEEE Journal of Solid-State Circuits
DOIs
Publication statusAccepted/In press - 2021

Keywords

  • Calibration
  • Current digital-to-analog converter (DAC)
  • dc-dc converter
  • Delays
  • digitally intensive phase-locked loop (DPLL)
  • inductor-capacitor (LC) oscillator
  • Jitter
  • multimodulus divider (MMDIV)
  • Oscillators
  • Phase locked loops
  • resample
  • ripple pattern estimation and cancellation
  • ripple replication and cancellation
  • Sensitivity
  • slope generator (SG)
  • successive approximation register (SAR) analog-to-digital converter (ADC)
  • supply pushing
  • supply ripple.
  • Voltage

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