Monolithic Integration of CMOS Charge Pumps for High Voltage Generation beyond 100 V

• Main Author: Shen, Lufei
• Format: Others
• Language: English; en
• Published: 2015
• Online Access: http://tuprints.ulb.tu-darmstadt.de/4397/1/Final_lufei_shen_diss.pdf; Shen, Lufei <http://tuprints.ulb.tu-darmstadt.de/view/person/Shen=3ALufei=3A=3A.html> : Monolithic Integration of CMOS Charge Pumps for High Voltage Generation beyond 100 V. Technische Universität, Darmstadt [Ph.D. Thesis], (2015)

Monolithic integration of step-up DC-DC converters used to be one of the largest challenges in high voltage CMOS SoCs. Charge pumps are considered as the most promising solution regarding in- tegration levels compared to boost converter with bulky inductors. However, conventional charge pump architectures usually show significant drawbacks and reliability problems, when used as on- chip high voltage generators. Hence, innovative charge pump architectures are required to realize the monolithic integration of charge pumps in high voltage applications. In this dissertation, three 4-phase charge pump architectures with the dynamic body biasing tech- nique and clock schemes with dead time techniques were proposed to overcome drawbacks such as body effect and reverse current problem of traditional Pelliconi charge pump. The influences of high voltage CMOS sandwich capacitors on the voltage gain and power efficiency of charge pumps were extensively investigated. The most reasonable 4-phase charge pump architecture with a suitable configuration of high voltage sandwich capacitors regarding the voltage gain and power efficiency was chosen to implement two high voltage ASICs in an advanced 120 V 0.35 μm high voltage CMOS technology. The first test chip operates successfully and is able to generate up to 120 V from a 3.7 V low voltage DC supply, which shows the highest output voltage among all the reported fully integrated CMOS charge pumps. The measurement results confirmed the benefits of the proposed charge pump architectures and clock schemes. The second chip providing a similar output voltage has a reduced chip size mainly due to decreased capacitor areas by increased clock frequencies. Fur- thermore, the second chip with an on-chip clock generator works independently of external clock signals which shows the feasibility of integrated charge pumps as part of high voltage SoCs. Based on the successful implementation of those high voltage CMOS ASICs, further discussions on the stability of the output voltage, levels of integration and limitations in the negative high voltage generation of high voltage CMOS charge pumps are held with the aid of simulation or measurement results. Feed- back regulation by adjusting the clock frequency or DC power supply is able to stabilize the voltage performance effectively while being easily integrated on-chip. Increasing the clock frequency can significantly reduce the required capacitor values which results in reduced chip sizes. An application example demonstrates the importance of fully integrated high voltage charge pumps. Besides, a new design methodology for the on-chip high voltage generation using CMOS technolo- gies was proposed. It contains a general design flow focusing mainly on the feasibility and reliability of high voltage CMOS ASICs and design techniques for on-chip high voltage generators. In this dissertation, it is proven that CMOS charge pumps using suitable architectures regarding the required chip size and circuit reliability are able to be used as on-chip high voltage generators for voltages beyond 100 V . Several methods to improve the circuit performance and to extend the functionalities of high voltage charge pumps are suggested for future works.