What is reference voltage/refence Voltage

Background: A reference or voltage reference is usually a high-stability voltage source used as a voltage reference in a circuit. As the scale of the integrated circuit increases. In particular, the development of system integration technology (SOC) has become an indispensable basic circuit module in large-scale, ultra-large-scale integrated circuits and almost all digital analog systems. Many integrated circuits and electrical circuit units, such as analog-to-analog converters (DAC), analog-to-analog converters (ADC), linear voltage regulators, and switching voltage regulators, all require precise and stable voltage standards. In a digital-to-analog converter, DAC selects and generates analog output from the DC reference voltage based on the digital input signal displayed on its input end. In a digital-to-analog converter, the DC voltage tomb is used together with the analog input signal to generate digital output signals. The reference voltage source is often used as the benchmark for system measurement and calibration in precision measuring instruments and widely used digital communication systems. Therefore, the reference voltage source plays an important role in analog integrated circuits. It directly affects the performance and accuracy of electronic systems. In recent years, the research on it has been very active, and the reference voltage source made of the dual-pole process has achieved high performance and accuracy. At the same time, since 1970s, due to the in-depth research on the basic theory and manufacturing technology of MOS transistor, coupled with the progress of circuit design and technology, MOS analog integrated circuit has developed rapidly. Among them, the CMOS circuit has become the mainstream of digital integrated circuit products because of its simple process, small device area, high integration and low power consumption. In this context, in order to obtain low-cost and high-performance analog integrated circuit products, a variety of high-precision analog circuits based on standard digital CMOS technology have attracted people's attention, it has become an important research area in Integrated electrical technology. Various high-precision reference voltage sources have broad development and application prospects due to their wide application in digital simulation systems. Basic Principles: The ideal reference voltage source should be provided with stable voltage in the circuit without the influence of power supply and temperature, the term "reference" indicates that the value of the reference voltage source should be more accurate and stable than that of the general power supply. Generally, the resistor voltage can be used as the reference voltage, but it can only be used as the offset voltage of the amplifier or provide the operating current of the amplifier. This is mainly because it has no regulator, so the stability of the output voltage depends on the stability of the power supply voltage. In addition, the forward voltage drop of the diode can be used as the reference voltage. It can overcome the shortcomings of the above circuit and obtain a constant reference voltage independent of the power supply voltage, but its voltage stability is not high, and the temperature coefficient is negative, about-2mV/℃. It can also use the breakdown voltage of a silicon regulator diode (steady voltage tube or zoneer tube) as the reference voltage. It can overcome some shortcomings of a forward diode as the reference voltage, but its temperature coefficient is positive, it is about + 2mV/℃. Therefore, the above types are not applicable to scenarios with high requirements on the reference voltage. As a result, with this urgent market demand and the constant efforts of designers, high-precision reference voltage sources have emerged, and there are a wide variety. From the perspective of working principle, there are three main types: Standard Battery, temperature compensation reference voltage regulator and integrated circuit solid reference voltage source (Integrated Reference Voltage Source ). 1. Standard Battery Standard battery can be divided into two types: saturated type and non-saturated type. The output voltage of the saturated standard battery is 1.018 V, and the long-term stable performance reaches 1 μV/year (that is, 1ppm/year). However, the temperature coefficient is large. When the temperature coefficient is close to 200 ℃, the total temperature coefficient is about-40 μV/℃. Because the temperature coefficient of positive and negative grades of saturated standard batteries is different, when the temperature difference between the electrodes is only 0.0010 ℃, it can cause changes of about 0.3pv. Therefore, positive and negative levels of temperature balance must be maintained during use. The temperature coefficient of standard non-saturated battery is small, which is about-5 μV/℃ when it is close to 20'c. However, the long-term stability is poor, and the annual change is greater than 20-40 μV/year. Both of the above two batteries have a temperature lagging effect and cannot be fully loaded. However, due to their low noise, stable potential, convenient manufacturing, and low cost, therefore, it is widely used in most precision power supplies that only require short-term stability. Ii. Temperature Compensation reference Pressure Control Tube The temperature coefficient of the Temperature Compensation reference stabilized pipe can be as low as 5 μV/℃, and it is small in size, light in weight and easy to integrate; however, there are many disadvantages, such as high noise, weak load capacity, poor stability, high reference voltage, and poor tonality. This type of reference voltage source is not applicable in portable and battery scenarios. Iii. Integrated Reference Voltage Source There are many types of reference voltage sources made by using semiconductor integrated circuit technology, such as the Integrated Reference source of a deep-Buried Layer voltage regulator, the Integrated Reference source of a bipolar transistor, and the Integrated Reference source of a CMOS Band Gap. The "band gap reference source" is a new type of device that emerged in the early 1970s S. its advent has led to a new leap in the indicators of the reference device. From these reference sources, you can obtain the reference voltages from 1.22v to l0v. Because it is based on the non-surface band gap mechanism, it is more stable than the surface-based voltage regulator, and the temperature coefficient can reach μV/℃ (2ppm/℃ ), the output resistance is extremely low, and more importantly, it does not require a 60ppm long-term stability. Due to its high precision, low noise, and advantages, the band gap reference is widely used in voltage regulators, data converters (A/D, D/A), integrated sensors, and large generators, as well as a single precision voltage reference, low temperature drift and many other micro-power calculations. From the perspective of circuit connection, there are two types of reference voltage sources. The first type is the three-end model (input, output, and public egress), also known as the series benchmark source. The main advantage of this benchmark is that the static current is relatively low, and the standard output voltage can be adjusted in advance, so that the output current can be large without losing precision. The other type is dual-end, also known as the parallel benchmark source. The main advantage of this benchmark source is its flexible working polarity, but its load requirements are strict and sometimes only non-standard voltage can be provided. Current Situation and Development: With the development of integrated circuits, especially system integration technology, the reference voltage source is more widely used. The complex and changing working environment and increasingly broad application space provide opportunities and challenges for the development of reference voltage sources. In particular, how to further reduce the temperature coefficient and noise of the reference voltage source, improve its voltage stability and long-term stability will become a topic of people's long-term attention and efforts. At present, the design technology that uses the carrier mobility and the temperature effect of the reading voltage in the mos tube to compensate each other has emerged. This indicates that with the rapid development of the large-scale and SOC Technology and the continuous application of various new technologies and new processes, the design technology of high-precision reference voltage source will continue to improve, with a broader space for development.