Research And Design Of Real Time Clock Chip With Calibration

Real Time Clock (RTC) has been widely used for consume electronics, which need accurate timing source for systems. Nowadays, Quartz oscillators provide an accuracy far superior to other conventional oscillator designs. However, Quartz crystals are sensitive to temperature variations and other factor such as package, and this crystal drift reduced the accuracy of RTC.At normal temperature(25℃), the accuracy of RTC is about±20 ppm. For this temperature drift character, this paper referred to crystal oscillator temperature compensation principle, according to the feature of RTC circuit, designed a calibration algorithm based on divide-chain frequency. The clock frequency could be trimmed by a set of digital calibration registers based on this algorithm. With this method, the calibration accuracy is±0.25 ppm, and the range of calibration is±32 ppm. Furthermore, this RTC could achieve self-calibration when used with MCU and temperature sensor.Moreover, this paper implemented the design and verification of RTC by top-down methodology after analyzed the calibration algorithm. In this paper, multi-clock domain synchronized problem has been analyzed, and then the circuit used to transfer data between I2C clock domain and timing clock domain has been presented. With this interface method, the circuit could be supported by EDA tools and will not increase the power. After Synthesis and Place & Route, this RTC has been verified by many verification methodologies.This paper use VerilogHDL to achieve front-end design, and then use EDA tools of Synopsys Company to accomplish back-end design and verification. After full chip post simulation and power diagnose, the results indicates that this design method meets the requirement of high precision and low power.