The Design Of High Precision And Low-dropout Negative LDO

In recent years, portable electronic products such as mobile phones, laptops and tablets update quickly.Domestic portable medical equipment and wearable devices such as smart band and smart glasses become consumption hot spots.Those demand puts forward high integration, high cost performance, high safety and high reliability requirements for power management products. For the advantages of high integration, low price, low noise, low power consumption and simple application, linear regulators stand out in many power management products. On the basis of output voltage, LDO can be divided into positive LDO and negative LDO. Negative LDO can provide clean power for primary IC components, such as GaAs FET Gate Bias, operational amplifier, Analog Digital Converter(ADC) and Digital Analog Converter(DAC) and so on. Therefore, the study of negative LDO is of great significance.Firstly the paper expounds the working principle and main performance index of negative LDO. Basis on that, a negative LDO with high accuracy and low dropout voltage is designed. A novel negative voltage bandgap reference(NBGR) circuit is put forward in this paper. By using a novel multilevel curvature compensation technology, the influence of temperature on the NBGR’ output voltage is reduced significantly. Thus the Temperature Coefficient of proposed negative LDO is optimized. Structure optimization of error amplifier is carried out in this paper. By means of folded cascode CMOS operational amplifier and Class A amplifier, the wide swing and high gain characteristic of the error amplifier are guaranteed, so as to improve negative LDO’ load regulation and linear regulation. Also by optimizing the size of the pass device, the dropout voltage of the proposed negative LDO is reduced, so as to improve the work efficiency of the system. In addition, in order to prevent proposed negative LDO from burning down, the over-temperature protection and over-current protection circuit are designed. The shut off module is added to control the working state of proposed negative LDO. The proposed negative LDO is mainly used to drive GaAs、GaN power amplifier and used as post regulator of switching supplies, which are working in negative power condition.Based on CSMC 0.5 μm BCD process, according to the function demand, firstly the overall structure of negative LDO is designed, and then each composition module is realized in detail. With the help of Cadence software, the optimization design and simulation of key modules was carried out. Lastly, the system performance index is simulated and verified. The results show that the output voltage is-3V. Under the worst load condition, when input voltage varies from-5.5V to-3.5V, the variation of the output voltage is only 9.516 mV, so the linear regulation is ±0.159%/V. Under-5V supply voltage, when the load current varies from 1mA to 500 mA, the variation of the output voltage is only 12.64μV, so the load regulation is ±8.43x10-7%/mA. When the temperature varies from-40℃ to 125℃, the variation of the output voltage is 1.153 mV, so the precision is±0.0384%. When the load current is 500 mA, the dropout voltage is as low as168.2 mV. The results show that various performance index meet the expected requirement. Besides layout design and verification was finished.