A 2.5-5.75-GHz Ring-Based Injection-Locked Clock Multiplier with Background-Calibrated Reference Frequency Doubler

Ahmed Elkholy, Daniel Coombs, Romesh Kumar Nandwana, Ahmed Elmallah, Pavan Kumar Hanumolu

Research output: Contribution to journalArticle


A low-jitter, low-power ring oscillator (RO)-based injection-locked clock multiplier (ILCM) is presented. It employs a background-calibrated reference frequency doubler to increase the RO noise suppression bandwidth, a digital delay-locked loop (DLL) to achieve second-order suppression of RO noise, and a digital frequency-tracking loop (FTL) to continuously tune the oscillator's free-running frequency and ensure a robust operation across process, voltage, and temperature (PVT) variations. A least-mean-square (LMS) algorithm is used to accurately cancel the deterministic jitter (DJ) caused by input duty cycle errors. Fabricated in the 65-nm CMOS process, the prototype ILCM occupies an active area of 0.09 mm2 and generates an output clock in the range of 2.5-5.75 GHz using a 125-MHz reference clock. At 5 GHz, it achieves an integrated jitter of 335 fsrms, while consuming 5.3 mW of power. This translates to the best reported figure-of-merit (FoM) of -242.4 dB for a ring-based ILCM at this high frequency.

Original languageEnglish (US)
Article number8691469
Pages (from-to)2049-2058
Number of pages10
JournalIEEE Journal of Solid-State Circuits
Issue number7
StatePublished - Jul 2019



  • Delay line
  • PLL
  • delay-locked loop (DLL)
  • digital phase-locked loop (PLL)
  • digitally controlled delay line (DCDL)
  • digitally controlled oscillator (DCO)
  • flicker noise
  • frequency doubler
  • injection locking
  • injection-locked clock multiplier (ILCM)
  • jitter
  • least mean square (LMS)
  • multiplying injection-locked oscillator (MILO)
  • phase noise
  • reference doubler
  • ring oscillator (RO)

ASJC Scopus subject areas

  • Electrical and Electronic Engineering

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