Based On The I ~ 2 C Bus Digital Temperature Compensation Real-time Clock Chip Design

The purpose of this paper is to research and design a multi-function real time clock (RTC), which is widely used in industrial control and consumer electronics.The paper studies the piezoelectric properties the temperature-frequency and Frequency Stabilization characteristic of the crystal, gives a method of RTC temperature compensation, by changing the load capacitance of the crystal oscillator, and shows a formula to calculate the value of the load capacitance, which is based on the temperature-frequency characteristic of the crystal. The temperature compensation method may automatically check the temperature by temperature sensor, and change analog temperature signal to digital signal by A/D converter, then look up the storage to get the load cap compensation value at the current temperature, finally finish the compensation for the crystal oscillator. The frequency generated by crystal oscillator is32.768kHz, which is more precise. At the range of-40℃to+85℃, the accuracy of RTC is±5ppm, as the precision error is0.432s in the day.The chip communicates with the external MCU by I2C bus. I2C bus developed by Philips is a serial bus interface, holds the biggest market share, and is widely used in many areas, especially in the consumer electronics, telecommunications and industrial electronics. I2C bus is2-wire bus, which saves hardware source. RTC supports I2C-bus’s fast speed mode400kbps.RTC includes seconds, minutes, hours, date of the month, day of the week, month and year with leap-year compensation until2099. It may select between12-hour and34hour clock display, which is used in the different situation. It also has alarm functions that alarm A and alarm B have different alarm functions by minutes, hours and date/day. And it has programmable square wave output function, as1Hz,4.096kHz,8.192kHz, and32.768kHz.The chip designed in the paper is a high-precision, multi-function RTC chip, which communicates with external devices by2-wire I2C bus. The0.18μm CMOS one poly four metal process is used to fabricate the chip. Up to now, the chip has been fabricated. After testing, all functions meet the requirements.