18.5 A 54MHz Crystal Oscillator with 30× 18.5 Start-Up Time Reduction Using 2-Step Injection in 65nm CMOS

Karim M. Megawer, Nilanjan Pal, Ahmed Elkholy, Mostafa G. Ahmed, Amr Khashaba, Danielle Griffith, Pavan Kumar Hanumolu

Research output: Chapter in Book/Report/Conference proceedingConference contribution


The start-up time of crystal oscillators (TSTART) is a major bottleneck in reducing the average power of heavily duty-cycled wireless /wireline communication systems [1]. Among all the reported schemes to reduce TSTART, techniques that increase initial noise amplitude by injecting a surge of energy into the crystal resonator are shown to be most effective [1-3]. These approaches are proven to be robust if the frequency of the injection signal is equal to the crystal oscillator (XO) frequency (FINJ = FX0), which is difficult to achieve across PVT with on-chip oscillators. Any mismatch (ΔF = FINJ - FX0) even as small as a few 100 ppm can greatly increase TSTART. Sweeping the injection frequency using a chirp oscillator [2]or dithering the injection frequency between two values [1]can partially alleviate this issue but because δ text{F} neq 0, this only reduces TSTART to about 14× the theoretical minimum in [2]. On the other hand, it was shown in [3] that the use of a precise injection period TINJ,OPT can help reduce TSTART even in the presence of large ΔF. TINJ,OPT must be chosen such that current in the motional branch of the resonator, im(t), reaches its steady-state value, Im,SS (im(TINJ, OPT) = Im,SS) as shown in Fig. 18.5.1 [3]. However, small TSTART and large tolerance to ΔF can be achieved only when Im,SS is very small, which translates to small XO output amplitude (VXO < 200mV) and degraded phase noise. For example, as illustrated in Fig. 18.5.1, TSTART ≈ TINJ,OPT because im(TINJ, OPT) = Im,SS1 even when ΔF is as large as 1000ppm. However, for Im,SS2 > Im,SS1, no TINJ can ensure im(TINJ) = Im,SS2 if ΔF > 1000ppm, thus greatly increasing TSTART. Therefore, ΔF must be small (<500ppm) to achieve a large VXO even with precisely-timed injection, a condition that is difficult to meet in practice even with the best-reported temperature-compensated on-chip oscillators [4]. In view of these drawbacks, we present a robust 2-step injection technique that can tolerate large ΔF and achieves close to theoretical minimum TSTART, large output swing and excellent phase noise. Fabricated in a 65nm CMOS process, the prototype XO achieves TSTART of less than 20 μs across the -40°C to 85°C temperature range, which is within 1.5× of the theoretical minimum and represents an over-30× reduction in TSTART compared to that of a normal/uninjected XO.

Original languageEnglish (US)
Title of host publication2019 IEEE International Solid-State Circuits Conference, ISSCC 2019
PublisherInstitute of Electrical and Electronics Engineers Inc.
Number of pages3
ISBN (Electronic)9781538685310
StatePublished - Mar 6 2019
Event2019 IEEE International Solid-State Circuits Conference, ISSCC 2019 - San Francisco, United States
Duration: Feb 17 2019Feb 21 2019

Publication series

NameDigest of Technical Papers - IEEE International Solid-State Circuits Conference
ISSN (Print)0193-6530


Conference2019 IEEE International Solid-State Circuits Conference, ISSCC 2019
Country/TerritoryUnited States
CitySan Francisco

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Electrical and Electronic Engineering


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