Design Of Calibrated Real-time Clock Chip Based On I2C

Real-time clock chip is a high-density specific integrated circuit,which can provide precise time benchmark and be suitable for all applications that require low power consumption and timing.With the rapid development of consumer electronics,the demand for real-time clock chips is increasing.At present,precise crystal oscillator is usually used as the clock source in real-time clock,and its accuracy is affected by the inherent frequency deviation of the crystal oscillator,the change of the parasitic capacitance,and the environment temperature.In order to improve the timing accuracy of clock chip at normal temperature,we make the following designs in this thesis:First,we integrate low-power constant voltage circuit to supply oscillator,which can improve the accuracy and stability of clock source by increasing the stability of oscillator supplied voltage.Second,an adjusting capacitor is integrated inside the chip,and a feasible fuse modification scheme is designed.By adjusting the load capacitance of the crystal oscillator to correct the clock source frequency,which lays the foundation for the further frequency calibration.Third,a frequency calibration algorithm based on digital way is designed.The algorithm can calibrate the clock frequency after dividing the frequency through a digital calibration register.It can also adjust the time accuracy without changing the output frequency of the crystal oscillator.The calibration runs once a minute,the calibration resolution is 1.02 ppm,and the calibration range is ±64.26 ppm.This thesis uses top-down design method to complete the design of clock chip,with low power consumption and less resources pin serial bus I2C adopted for the external communication interface.The design includes clock counting module,alarm module,calibration module,I2C communication interface module,oscillator circuit module.We perform simulation and validation by using the EDA tool,which is used for integrated circuit design.In our simulations,the 0.5μm-5 V CMOS process is adopted.It is verified that the following functions can be realized:counting time,adjusting the leap year automatically,adjusting the month of the days,24 hour and 12 hour counting,and two alarm modes:one is about minutes and hours,and the other is about minutes,hours and weeks.In addition,the clock chip can output programmable square wave,with adjustment timing counting precision.The clock chip layout final area is 0.842*0.996 mm2.