A Fast Startup Crystal Oscillator Based On Automatic Phase-error Correction Technique

In low-power Io T systems,wireless sensor nodes operate in a low duty-cycle state to reduce power consumption.The crystal oscillators that provide reference clocks for these nodes may take several milliseconds to wake up,which undoubtedly increases the average power consumption of the system.Therefore,the crystal oscillators in an intermittent duty demand fast startup for average power consumption reduction.This article designed a fast startup crystal oscillator based on an automatic phase-error correction technique.Firstly,the equivalent circuit of the crystal oscillator was analyzed,and the theoretical formula of the startup time was derived.Based on the above,the feasibility of the automatic phase-error correction technique proposed in this work was analyzed in detail.For the first time,single ended injection technology has been applied to the field of fast start crystal oscillators,successfully interpreting the waveforms at both ends of the crystal under single ended injection.Then the overall circuit design was completed,where one end of the crystal is used for injection while the other is used to obtain phase-error accumulation information.The phase-error correction was conducted with the energy injection,which can solve the problem of blindness during dual end injection.At the same time,it can ensure the continuous injection of energy without being limited by phase-error accumulation.There is a high tolerance for the frequency mismatch between the injection signal and the crystal resonance,reducing the difficulty for the design and calibration of on-chip integrated oscillators.This article completes the design of a fast startup crystal oscillator in a 40nm CMOS process,with a core layout area of 0.05mm~2,a load capacitor of 6p F,and an output frequency of 16MHz.The measurement results show that within a temperature range of-20～85℃,the startup time of the crystal oscillator designed in this article varies by only±4.5%.The startup time at room temperature is17.5μs.Compared with traditional injection technniques,this work achieved a 249×startup time reduction,a startup energy of 9.2n J and a steady-state power of 84μW.