采用两步式数字校准的低温漂松弛振荡器

A High-Precision Low-Power and Low-Temperature-Drift Relaxation Oscillator with Two-Step Digital Calibration

针对传统片上振荡器设计面临的时钟频率难以实现高精度校准的问题,提出基于二分搜索法的数字校准方法,实现了振荡频率校准并提高了校准的线性度。校准算法采用了粗校准加细校准的两步式校准过程,大大增加了频率校准范围。针对振荡频率的温度漂移问题,提出了新的温度补偿方案,在传统一阶温度补偿的基础上,增加了亚阈值电流自补偿的高阶补偿机制,大大降低了温度变化对输出频率的影响。在校准电路的设计中,合理设置开关电阻阵列的温度系数以保证输出频率的校准不影响输出频率的温度稳定性。对振荡器版图提取了寄生参数,并进行了仿真,仿真结果表明:经过所提频率校准和温度补偿方案,典型情况下振荡频率误差小于0.04%;在-40~125℃温度范围内频率误差小于±0.12%;2.5~5.5 V电源电压范围内频率随电源电压变化误差小于±0.13%;电路工作电流为47.6μA,完成一次校准时长不超过2.7 ms。该振荡器可用于物联网、处理器等应用,可以取代片外晶体振荡器,能够降低系统成本和体积。

Given the difficulty in achieving high-precision clock frequency calibration of traditional on-chip oscillators,this study proposes a digital calibration method based on a binary search algorithm and realizes frequency calibration with high linearity for a relaxation oscillator.The calibration algorithm adopts a two-step calibration approach,consisting of coarse calibration and fine calibration,which significantly expands the frequency calibration range.To solve the problem of temperature drift of oscillation frequency,a new temperature compensation scheme is proposed in this study.This scheme introduces a high-order compensation mechanism of subthreshold current self-compensation on the basis of the traditional first-order temperature compensation,which greatly reduces the influence of temperature changes on the output frequency.Additionally,the temperature coefficient of the switch resistor array is reasonably set to ensure that the frequency-temperature characteristics of the oscillator frees from the negligible effect by the calibration of the output frequency.Parasitic parameters are also extracted for the oscillator layout and simulated.The simulation results demonstrate that with the frequency calibration and temperature compensation schemes in place,the frequency error is lower than 0.04%under typical circumstances.The frequency errors are less than±0.12% and±0.13% within the temperature range of-40℃ to 125℃,and supply voltage range of 2.5 V to 5.5 V,respectively.The overall circuit operates with a current of 47.6μA,and the duration of a single calibration process is shorter than 2.7 ms.The oscillator can be used in applications such as IoT and microprocessors to replace crystal oscillators,thereby decreasing the system cos t and volume.