Research Of Fast On-Chip CMOS Charge Pump

Charge pump circuits that make use of charge accumulating in the capacitor pump charge upward to produce higher voltage than the available supply voltage. They are widely used in the field which needs high voltage, such as serial port communication circuits, EEPROM and DRAM. The Charge pump circuits are used for programming and erasing the floating-gate devices in EEPROM. If the speed of pumping charge is slow, the data won't be rewritten rapidly for EEPROM and the data may lose or misrepresent. For the sake of decreasing the rise time of the output voltage of the charge pump, a circuit of on-chip charge pump system for use in EEPROM is designed.The design is based on 0.5μm CMOS technology. The charge pump system designed is composed of clock generation circuit, charge pump nuclear and voltage adjusting circuit. The clock generation circuit consists of voltage reference source, common source voltage amplifier, VCO and sequence circuit.The clock generation circuit outputs both high frequency clocks of the duty cycle about 30%. The charge pump driven by these signals avoids the bad phenomenon of charge leak dramatically, which makes the rise time of the output voltage decrease prominently. With the consideration of the initial node voltage, an improved Dickson circuit is proposed, which reduces the rise time of the output voltage further. The output voltage of the charge pump nuclear is changed by the adjusting circuit, which makes the voltage suit with the operation voltage of EEPROM. The charge pump system with an enable signal can be turned on and shut down, so that the supply power consumption is saved.Each module and the entire system of the on-chip charge pump are simulated by HSPICE. The result indicates that the clock frequency is 2.071MHZ and the duty cycle is 31.565% when supply voltage is 5V. The rise time from 5V to 16V only needs 51.650μs for the charge pump system and the maximum output voltage is 17.691V. The static current is 8.611μA when the charge pump is out of work. The data satisfy the target. The on-chip charge pump system has many advantages of the voltage rising rapidly and the circuit implemented easily. It can provide general voltage and high voltage for EEPROM to read, write and erase. It can be used in the chips that need fast speed of reading and writing.