What Is a Voltage Reference?

The reference voltage refers to a voltage in the circuit that can be kept constant regardless of the load, power supply, temperature drift, time, etc. Reference voltages can be used in voltage regulators for power supply systems, analog-to-digital converters and digital-to-analog converters, and many other measurement and control systems. The size of the reference voltage varies in different applications. For example, in a general computer power supply system, the error of the reference voltage is not greater than one to a few percent of its nominal value, and the reference voltage of the laboratory Standards have higher stability and accuracy, measured in parts per million.

Refers to the voltage value used as a reference point when measuring the voltage value. When measuring voltage, ground is generally used as the reference point. When measuring, the negative terminal of the voltmeter is grounded and the positive terminal is connected to the measured point. The measured value is the voltage value of the measured point. Of course, instead of using ground as the reference point, a reference voltage (for example, + 2V) can be used as the reference point. If the voltage of the measured point relative to the ground is + 5V, the voltage of the point relative to the reference voltage is + 3V.

This is the same as measuring height. In adjustable power ICs, Vref is usually equal to 1.23V, and its value multiplied by (1 + R2 / R1) is the output voltage value.

A voltage reference or Voltage Reference usually refers to a highly stable voltage source used as a voltage reference in a circuit. With the increasing scale of integrated circuits. Especially the development of system integration technology (SOC), it has also become an indispensable basic circuit module in large-scale, ultra-large-scale integrated circuits and almost all digital and analog systems.

Many integrated circuits and circuit units, such as digital-to-analog converters (DACs), analog-to-digital converters (ADCs), linear regulators, and switching regulators, require precise and stable voltage references. In a digital-to-analog converter, the DAC selects and generates an analog output from a DC reference voltage based on the digital input signal present at its input. In the analog-to-digital converter, the DC voltage is used together with the analog input signal. Generate a digitized output signal.

In precision measuring instruments and widely used digital communication systems, the reference voltage source is often used as a reference for system measurement and calibration. Therefore, the reference voltage source occupies a very important position in the analog integrated circuit, which directly affects the performance and accuracy of the electronic system. In recent years, research on it has also been very active, and the reference voltage source made by the bipolar process has been able to achieve quite high performance and accuracy.

At the same time, since the 1970s, due to in-depth research on the basic theory and manufacturing technology of MOS transistors, coupled with advances in circuit design and process technology, MOS analog integrated circuits have 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, high-performance analog integrated circuit products, various high-precision analog circuits based on standard digital CMOS processes have attracted attention and 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 and analog systems.

The ideal reference voltage source should not be affected by the power supply and temperature, and can provide a stable voltage in the circuit. The term "reference" is indicating that the value of the reference voltage source should have higher accuracy and stability than general power supplies.

In general, the resistor divider voltage can be used as the reference voltage, but it can only be used as the bias voltage of the amplifier or provide the operating current of the amplifier. This is mainly because it does not have its own voltage regulation effect, so the stability of the output voltage depends entirely on the stability of the power supply voltage. In addition, the forward voltage drop of the diode can also be used as the reference voltage. It can overcome the shortcomings of the above circuit and obtain a constant reference voltage that does not depend on the power supply voltage, but its voltage stability is not high and the temperature coefficient is negative. About -2mV / . It is also possible to use the breakdown voltage of a silicon Zener diode (referred to as Zener or Zener for short) as the reference voltage, which can overcome some of the shortcomings of the forward diode as the reference voltage, but its temperature coefficient is positive, about + 2mV / . Therefore, none of the above are suitable for occasions that require a high reference voltage. Therefore, under this urgent market demand and the continuous efforts of designers, high-precision reference voltage sources have emerged at the historic moment, and there are many types.

From the perspective of the working principle, it is mainly divided into three categories: standard batteries, temperature-compensated reference voltage regulators, and integrated circuit solid-state reference voltage sources (referred to as integrated reference voltage sources).

Reference voltage: If the reference voltage you choose is 5v and your ad is 12-bit, then when your input voltage is 5v, the display of your microcontroller should be 4095. If the input is 0v, the value in the microcontroller is 0, the value of the middle point has a linear relationship, that is, if your input is m, then the value of the single-chip microcomputer is 4096 * m / 5. In this way, you know the value of the single-chip microcomputer to calculate how much your input is.

There is also an inductor added between the signal ground and the analog ground to eliminate interference, just like using a capacitor between vcc and GND. The reference voltage during ad conversion is the standard voltage of the internal T-line network. The reference voltage can be considered as your highest upper limit voltage (not exceeding the power supply voltage). When the signal voltage is low, you can lower the reference voltage to improve resolution. After changing the reference voltage, the voltage value in the same binary representation will be different. The largest binary representation is your reference voltage. When calculating the actual voltage, you need to take the reference voltage into account. The stability of the reference voltage has a great impact on your system performance.