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18.5 A 54MHz Crystal Oscillator With 30× Start-Up Time Reduction Using 2-Step Injection in 65nm CMOS | IEEE Conference Publication | IEEE Xplore

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


Abstract:

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]....Show More

Abstract:

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 ΔF ≠ 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 ...
Date of Conference: 17-21 February 2019
Date Added to IEEE Xplore: 07 March 2019
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Conference Location: San Francisco, CA, USA

References

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