Design Of High-stability RC Oscillator With Self-calibration And Frequency-locked

The shrinking Io T nodes are becoming more and more demanding on chip size.In order to reduce size of external clock crystals,on-chip RC oscillator has become an effective alternative.However,temperature,supply voltage and internal noise all cause the frequency deviation of RC oscillator.When the frequency deviation accumulates and produces a large timing error,serious problems such as synchronization mismatch and data packet loss will occur.In view of above situation,a high-stability RC oscillator circuit with self-calibration and frequency-locked in real time is proposed.The frequency-locked loop with negative feedback avoids accumulation of frequency deviation,improves the long-term stability determined by internal noise,which is the basis for a high-stability clock.Aiming at the jitter accumulation problem of an open-loop RC oscillator and the design trade-off of a comparator,based on the traditional RC dual-branch charging and discharging structure,the combined structure of error amplifier and voltage-controlled oscillator is adopted to replace the comparator to generate the clock.On the one hand,absolute influence of the comparator delay on the frequency is eliminated,and the compromise between power consumption and comparator delay is solved.On the other hand,a frequency-locked loop is formed,and the output frequency is converted into an error voltage in real time through a switched capacitor.The error is amplified,and the control voltage is generated to control clock frequency.For clock stability of the self-calibrated RC oscillator,the specific relationship between non-ideal factors and frequency deviation is analyzed and summarized,including offset voltage,resistance temperature drift,clock coupling,high temperature leakage,and current mirror copy ratio deviation.By analyzing temperature and power supply voltage dependence of the factors,the specific relationship between temperature stability and supply voltage stability are proposed.On the basis of this analysis,in view of the contradiction between the temperature and supply voltage stability of charging and discharging dual-branch,a current mirror with a chopper structure and a symmetric switch array structure are proposed,which solves all of problems of clock coupling,high temperature leakage and current mirror mismatch,ensuring the constant ratio of charge and discharge current.For the resistance and offset voltage with obvious linear temperature coefficient,a linear temperature compensation resistor array is designed to obtain the minimum frequency temperature drift,and a two-point trimming circuit is designed to improve the linear coefficient mismatch caused by the process mismatch,ensuring the high-stability among various process angles.Based on the TSMC40nm process,the high-stability RC oscillator with self-calibration frequency-locked,occupies the area of 0.0986mm~2,consumes only 68n W and generates the target frequency of 33k Hz under the supply of 0.7V at TT process.The frequency deviation is reduced to0.16%over the full temperature range of-40??90?,with a temperature coefficient of 12.3ppm/?.In the power supply range between 0.7V and 1V,the deviation of 0.042%exhibits a linear sensitivity of 0.13%/V.The long-term Allan deviation floor is only 7ppm for measurement intervals over 1s.To sum up,the self-calibration and frequency-locked RC oscillator can generate the high-stability clock over the influence of process,ambient temperature,power supply voltage and noise.