Mcu Chip Reset Circuit With Multi-mode Clock System Design

The applied fields of MCU are extensive, such as industry control, intelligent instrument and consumption electron. For a MCU chip, it mainly realize the logical function.however, the system circiuts of reset and clock which ensure the MCU chip work also paly a important role. Nowadays the monitor circiuts are developing toward the direction of multifunction. In the early day, there is only voltage detector on chip.Now, more and more assistant functions are integrated on chip, such as the watch_dog_timer and data protected.System clock source developed from single outer to inside and outer.In this thesis, a monitor circuits system and multi-sources clock system were designed for a MCU chip based on the analyse of domestic and overseas papers about voltage detector, programme monitor and oscillator. The primary works are listed as below:1. Designed a band_gap voltage comparator circiut.it was used to realize power_on_reset and brown_out detector.when the power supply reached the safety voltage point, the POR will generate a pulse to initialize the MCU. The BOD will lock the MCU after the supply drop out of the detector point, it avoid the MCU executed error. The voltage point of the POR and the BOD are adjustable and have individual voltage point.2. Designed a 10_bits timer.it can be used as watch_dog timer, power_on timer and oscillator timer throught configuration. The overflow time of wdt can be set from 1.8ms to 2.3s according to user programme.3.Designed a main clear circuit which can filter interfere pulse under 50ns.once the circuit detector a right reset signal, it will generate a reset pulse more than 200ns.4. Designed a pierce crystal oscillator of 20MHz, provide a high accuracy clock for system.5. Designed a RC oscillator of 4MHz on chip which have a novel band_gap voltage reference and a stable current over a wide temperature come from combining PTAT current and CTAT current.It take the framework of two comparators so as to eliminate the frequency error result from the comparator delay. After the oscillator embeded in chip, the frequency can be trimed through a register. The accuracy of the oscillator can be adjusted in the range of one percent.The design was based on the csmc 0.5μm CMOS process. The simulation results obtained show that the functions and performances of this monitor circiuts system and multi_sources clock system meet the spec well.