A low-voltage differential AC regulator [3] is a DC AC regulator whose input voltage is greater than the output voltage. It has the characteristics of stable output voltage, small output ripple and low noise. LDO also has the characteristics of small package size and few external components. Because of its advantages, LDO is widely used in communication equipment, automotive electronics, industrial and medical equipment. At present, with the development of a large number of portable electronic devices such as PDA, mobile phones and MP3 are widely used in people's life and work. These portable electronic devices are small and mostly powered by batteries. LDO is also suitable for this electronic system.

Since there is a voltage difference between the input voltage and the output voltage of the LDO, when a certain load current is output, the LDO consumes Power=UI. This affects the efficiency of the LDO. If this power is very large, it will also cause the power transmission tube on the LDO to heat up, requiring a huge heat sink, which is not conducive to the application of LDO in portable electronic devices. If this voltage difference can be reduced as much as possible, LDO can not only stabilize the voltage, but also have high efficiency, and will not heat up when the output of large load current.

At present, wireless communication devices are playing an increasingly important role in our work and life, such as mobile phones, wireless netbooks, Bluetooth and so on. These wireless devices are small in size, and as handheld mobile devices, they are generally powered by batteries, so LDO with small size and few external components is a suitable power supply solution.

However, the switching action of radio frequency transmitter of wireless communication equipment will produce noise, which seriously affects the quality of power supply. For example, the switching frequency of a mobile phone RF power amplifier is 217Hz. RF power amplifiers draw A large current (typically up to 1.7A) from the power supply each time they switch, which causes a sudden voltage drop of up to 500mV across the battery's equivalent series resistance (ESR). For SOCs with built-in high-resolution audio converters and audio amplifiers, this change will compromise the overall performance of the SoC, especially the audio processing quality of the audio module will be severely affected, and there will be buzzing noise. The characteristic of this noise is audible because it is not random noise. In fact, noise with amplitude as low as 10mV can be heard by the human ear if it occurs at a fixed rate. This noise is more unacceptable than random noise with a larger amplitude.

A low-voltage differential linear regulator (LDO) uses a transistor or field-effect transistor operating in a linear region to subtract excess voltage from the applied input voltage to produce a stable output voltage. The so-called voltage drop refers to the minimum difference between the input voltage and the output voltage required by the voltage regulator to maintain the output voltage within its rated value of 100mV.

LDO(Low voltage Difference) regulators with a positive output voltage typically use a power transistor (also known as a transmission device) as a PNP. This transistor allows saturation, so the regulator can have a very low voltage drop, usually around 200mV; In contrast, conventional linear regulators using NPN composite power transistors have a voltage drop of about 2V. A negative output LDO uses an NPN as its transfer device, which works similarly to a PNP device with a positive output LDO. The new development uses CMOS power transistors, which can provide the lowest voltage drop. For CMOS, only the voltage drop on the regulator is caused by the on-resistance of the load current of the power supply device. If the load is small, the voltage drop produced by this method is only a few tens of millivolts.