RTC Design With Power-down Emergency Processing Capability

Real-time Clock(RTC)chips are widely used in various electronic products.With the vigorous development of information technology and the expansion of the consumer market,higher requirements are placed on the power supply voltage and output accuracy of RTC.And the complex application scenarios make the versatility of RTC chips not guaranteed.Based on the above-mentioned problems,this thesis proposes and designs a RTC circuit with power-down emergency processing capability.The RTC with power-down emergency processing capability includes configurable crystal oscillator,power-down emergency processing circuit,interface circuit,timing circuit and related registers.The configurable crystal oscillator and power-down emergency processing circuit are the research focus of this design.The configurable crystal oscillator adopts the structure of the Pierce oscillator.The use of Pseudo-Resistor instead of the feedback resistor greatly reduces the layout area.The power consumption control circuit ensures that the crystal oscillator starts to oscillate quickly and maintains oscillation with low power consumption.The calibration and test circuit improves the reliability and testability of the chip,and the output frequency of the crystal oscillator can be calibrated by configuring the 6bit register.The power-down emergency processing circuit adopts three power supply strategies: standard power supply,wide power supply and backup power supply.The standard power supply is used to input the 1.8V supply voltage from the outside directly,making full use of the low power consumption of the RTC.The wide power supply and the backup power supply can be automatically switched at the threshold to realize emergency treatment of power failure.The wide power supply range is 2.5V?5.5V and the backup power supply can use a 3V button battery and a 1m F capacitor to cope with different application scenarios.The circuit output is guaranteed by the LDO to output a stable 1.8V supply voltage.The power-down emergency processing circuit also has the functions of low-voltage monitoring and power-on reset.When the power supply voltage is insufficient,an alarm or reset signal is sent to the outside in advance to remind the user of power failure and insufficient battery power.The RTC circuit with power failure emergency handling capability is based on the0.18?m BCD process and adopts a top-down design method.Starting from the top-level architecture,the design and simulation of each module of the circuit are implemented step by step,and finally the layout design and post-simulation are completed.The simulation results show that the designed RTC with power failure emergency handling capability can complete the expected functions,the circuit operating temperature range is-65??125?,the power input is compatible with 2.5V?5.5V,and the backup power supply is compatible with 3V button battery and 1m F Capacitor.When the power supply is powered off,it can automatically switch and ensure the stability of the power supply voltage of the rear stage.The theoretical maximum calibratable accuracy of the configurable crystal oscillator is ±2.17 ppm,the minimum operating current is 25.43 n A@1.8V,the minimum start-up time is 81 ms,and the duty ratio of output is close to 50%.