According to the different structure of internal reference voltage generation, voltage reference can be divided into two categories: bandgap voltage reference and voltage reference of voltage regulator. The bandgap voltage reference structure is to connect a forward biased PN junction and a voltage related to VT in series, and realize temperature compensation by using the negative temperature coefficient of PN junction to cancel the positive temperature coefficient of VT. The voltage reference structure of the zener diode is to connect a sub-surface breakdown zener diode and a PN junction in series, and realize temperature compensation by using the positive temperature coefficient of the zener diode and the negative temperature coefficient of the PN junction to cancel. Sub-surface breakdown is beneficial to reduce noise. The voltage reference of the voltage reference of the voltage stabilizer is relatively high (about 7V); However, the reference voltage of bandgap voltage reference is relatively low, so the latter is more widely used when low power supply voltage is required. According to different external application structures, voltage reference can be divided into two types: series type and parallel type. In application, the series voltage reference is similar to the three-terminal regulated power supply, and the reference voltage is connected in series with the load; The parallel voltage reference is similar to the voltage regulator tube, and the reference voltage is connected in parallel with the load. Both band gap voltage reference and voltage reference of voltage regulator can be applied to these two structures. The advantages of series voltage reference are that only the input power supply is required to provide the static current of the chip and the load current when the load exists; The parallel voltage reference requires that the set bias current is greater than the sum of the static current and the maximum load current of the chip, which is not suitable for low power consumption applications. The advantage of parallel voltage reference is that it can meet a wide input voltage range by using current bias, and it is suitable for floating voltage reference.