DAC：Equipment for Converting Digital Data to Analogue Signals

Digital to Analogue Converters (DAC)

A digital-to-analogue converter, or D/A converter, or DAC for short, is a device that converts digital data into an analogue signal. According to the Nyquist-Shannon sampling theorem, any sampled data can be perfectly reconstructed by means of the bandwidth and Nyquist criteria.

DACs can accurately reconstruct sampled data into analogue signals. Digital data can be generated by microprocessors, Application Specific Integrated Circuits (ASICs) or Field Programmable Gate Arrays (FPGAs), but the final data needs to be converted to an analogue signal in order to interact with the real world.

DAC Basic Principle

DACs are devices that convert digital signals into analogue signals for the purpose of connecting digital and analogue devices at their interface, with the analogue signal at the output representing the digital signal at the input. According to their principle, DACs can be divided into Nyquist and oversampling types, and according to their structure, Nyquist converters can be broadly divided into the resistive divider, R-2R weighing type, charge distribution type and current-driven type. structure.

Composition and Characteristics of DAC

The DAC consists of a digital register, an analogue electronic switch, a bit power network, a summing operational amplifier and a reference voltage source (or constant current source). Each digit of the digital quantity stored in the digital register is used to control the analogue electronic switch of the corresponding bit so that the bit with a digit of 1 generates a current value proportional to its bit power on the bit power network, which is then summed by the operational amplifier and converted into a voltage value.

Depending on the bit power network, different types of DACs can be formed, such as power-resistor network DACs, R-2R inverted T-resistor network DACs and single value current type network DACs. The conversion accuracy of a power-resistor network DAC depends on the reference voltage VREF, as well as the accuracy of the analogue electronic switch, the operational amplifier and the value of each power resistor. It has the disadvantage that the resistance values of each power resistor are different, and when there are many bits, their resistance values are very different, which makes it very difficult to guarantee the accuracy, especially for the production of integrated circuits, so the circuit is rarely used separately in integrated DACs.

It consists of a number of identical R and 2R network sections, each corresponding to an input bit. The R-2R inverted T-shaped resistor network DAC is one of the faster and more widely used. Compared to the power resistor network, it has only two resistance values, R and 2R, thus overcoming the disadvantages of having many power resistors with widely varying resistance values.

Current type DAC is a constant current source switched into the resistor network, the constant current source internal resistance is extremely large, equivalent to an open circuit, so together with the electronic switch, the impact on its conversion accuracy is relatively small, and because the electronic switch is mostly non-saturated ECL switching circuit so that this DAC can achieve high-speed conversion, conversion accuracy is higher.

Main Applications of DAC

DAC digital-to-analogue converters are used in many digital signal processing applications and many more, some of which are briefly listed below.

1. Audio amplifiers

DACs are used to generate DC voltage gain through microcontroller commands. Typically, the DAC will be integrated into the entire audio codec including the signal processing functions.

2、Video encoder

The video encoder system will process the video signal and send the digital signal to various DACs to produce analogue video signals in various formats while optimising the output level. DACs may be integrated into these ICs, just as they are in audio codecs.

3. Electronic displays

Graphics controllers typically use look-up tables to generate data signals sent to video DACs for analogue outputs, such as red, green and blue (RGB) signals to drive displays.

4. Data acquisition systems

The data to be measured is digitised by an analogue-to-digital converter (ADC) and then sent to the processor. The data acquisition will also include a process console where the processor sends the feedback data to the DAC for conversion to analogue signals.

5. Calibration

The DAC provides dynamic calibration for gain and voltage offset to ensure the accuracy of the test and measurement system.

6、Motor control

Many motor controls require voltage control signals and DACs are ideally suited to such applications which may be driven by a processor or controller.

7. Data distribution systems

Many industrial and factory production lines require multiple programmable voltage sources, which can be generated by a set of multiplexed DACs, such as the model AD5541ABRMZ. The use of DACs allows the voltage to be dynamically changed during system operation.

8. Digital potentiometers

Almost all digital potentiometers are based on a string DAC architecture. With some reorganisation of the resistor/switch array and the addition of an I2C compatible interface, a fully digital potentiometer can be implemented.

9. Software radio

DACs are used in conjunction with digital signal processors (DSPs) to convert signals into analogue signals for transmission in mixer circuits and then to the power amplifiers and transmitters of the radio.

Conclusion

Digital-to-analogue converters (DACs) are common in electronic circuits and are used in a wide range of applications. It is important to note that when using a digital-to-analogue converter (DAC) again, it is necessary to take into account relevant parameter criteria such as power supply rejection ratio, operating temperature range, detuning error, gain error and non-linearity error.

More specific DAC information can be found here.