Design Of A Real Time Clock Chip Based On The I~2C Bus With Digital Temperature Compensation

The clock circuit is an important part of modern electronic products, it provides stable and accurate clock for the system. With the development of the integrated circuits, the clock circuit is also beginning to be integrated. However, temperature affects the performance of clock IC.This paper proposed the design of a quartz crystal clock chip with temperature compensation in HHNEC 0.25 um CMOS process. This paper described a complete design of the clock chip, which includes the structure design, circuits design and debugging test. First, this paper determined the core parameters of the clock chip according to the requirements and gave the design of the chip architecture. Second, this paper introduced the design of RTC, which includes a oscillator, a bus interface and a clock based on registers. This part also includes the low pressure detection circuit, the oscillation wave detection circuit, POR circuit and etc. Then this paper came into the part of digital temperature compensation. Starting from the analyses of the temperature characteristics of the quartz crystal, I determined the temperature compensation scheme after putting forward the concept of temperature compensation. The digital method is used to stabilize the oscillation frequency by changing the loading capacitance of the clock. The temperature compensation circuits include the temperature detection circuit, the reference circuit and an SAR ADC. Finally, this article gave the test results of some chip samples. What’s more, the debugging method of the chips is also very important. A simple and effective method of debugging will determine the practice value of the chips. The main reason that affects the qualified rate lies in the damage of the quartz crystal.Although the samples failed to meet business requirements, but this paper proposed a complete design of the temperature compensated clock chips. The samples have a accuracy within ± 10 PPM and the high yield can be ensured without considering the economic significance.