A New Negative Charge Pump Circuit For 3D NAND Memory

The voltage of the power supply is getting smaller with the contraction of the 3D NAND memory size.However,the erasing and reading operation of the memory need power supply to provide different voltage,the charge pump is widely used in the 3D NAND memory because it can convert the high-voltage and low-voltage,and it contains the advantages such as lowpower consumption,simple structure and etc.Due to the high precision and real-time of memory,the charge pump needs low ripple,high conversion efficiency and high starting speed,the author researched at the erasing operation of the negative charge pump of the 3D NAND flash memory.The traditional negative charge pump circuit has the problem of reverse current,which leads to large ripple,low conversion efficiency,slow-starting speed and high consumption,it also requires two negative charge pump units to be cascaded to generate twice the negative voltage,causing the chip area too large,so the author adopted four-phase non-overlapping clock control;aiming at the problem of the comsumption and output ripple,the author adopts the control method of selecting the clock frequency.The main content of the thesis is as follows:(1)Compared with the traditional negative charge pumps,the circuit is equipped with small area,low ripple and high starting speed.The author putted forward and improved the four-phase cross-coupled negative charge pump circuit,selected the clock frequency,widthto-length ratio of the switch tube and the pump capacitor.The results have identified that the output ripple and power consumption goes by 86% and 42% separately.(2)The author designed a new control method to select the clock frequency by analyzing and comparing various control methods.The author designed the negative charge pump,bandgap reference circuit,voltage controlled oscillator circuit,four-phase non-overlapping clock generation circuit,clock frequency selection circuit through YMTC 0.18μm process in the soft Candence.The results have identified that conversion efficiency is 94%,the output voltage ripple is 3m V and starting time is 1μs which were improved by further simulating the whole system through spectre and Finesim.