| TFT-LCD has some characteristics such as low voltage, micro power dissipation and complanation, can be widely used in portable electronic fields, such as mobile phone, PDA, MP3 and so on. In the recent years, portable electronic equipment has been fast developed and become more popular, which bring on the up rush of TFT-LCD and its bias power supply. In order to meet the demand of different input voltage or output current application, R&D on TFT-LCD bias power supply has become the hotspot of power supply market.A high-efficiency, auto-adjustable charge pump for TFT-LCD source driver has been designed in this thesis. As the voltage gain of common charge pump is settled, the transition efficiency will become lower and lower along with the input voltage rising. The charge pump in this thesis can change it's voltage gain and choose whether stop switching or not automatically in order to improve transition efficiency and reduce power dissipation.Based on fundamental principle and basic topology of charge pump circuit, whole framework and sub-blocks of 1.5×/2×high-efficiency, auto-adjustable charge pump circuit are designed, and some performance parameters are analyzed in details. We discussed how to improve the efficiency by improving controlling mode and optimizing the design of switches. Then we analyze some important modules in details such as input voltage check, thermal shutdown, mode change, voltage select, timer circuit, etc. At last, we simulated all the sub-blocks and whole circuit by Hspice.The charge pump has been designed using UMC 0.6μm BiCMOS process. The working frequency is 250KHz, it can provide 25mA output current at most in the wide input voltage range from 2.7V to 5.5V and the transition efficiency is 66% at least. The most excellent characteristic is that it can change working mode according to fixed input and output voltage to improve the efficiency. The simulating results show that the R&D of the circuit has succeeded basically. |
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