0 Introduction

Before discussing Analog to Digital Converters (ADC) and Digital to Analog Converters (DAC), let’s first clarify what analog signals and digital signals are.

Analog signals can be understood as physical quantities from the real world, but these quantities are electrical signals. For example, radio signals, etc. The characteristics of analog signals are that they are continuous in time and amplitude. Their advantage is that they are intuitive and easy to implement. However, they also have some drawbacks, such as being susceptible to various noise interference. If we want to process analog signals, we need to design various circuits, which can be cumbersome.

Digital signals are signals processed by sampling analog signals, characterized by discrete time and discrete amplitude. The advantage of digital signals is that they compensate for the shortcomings of analog signals. For example, digital signals have strong anti-interference capabilities, are easy to store, and facilitate various computations.

Since computers have almost taken over every field, the processing of signals in these fields must be converted into signals that computers can understand, which are digital signals. Therefore, to convert analog signals into digital signals, we need a device called an Analog to Digital Converter (ADC). Conversely, since ADC converts analog quantities into digital quantities, there is also a device that can convert digital quantities back into analog quantities, called a Digital to Analog Converter (DAC). The functions of ADC and DAC are illustrated in the figure below (ADC and DAC are sometimes abbreviated as A/D and D/A).

1 Classification and Performance Indicators of ADC

ADC can be classified mainly into integrating type, successive approximation type, parallel comparison type, sigma-delta type, capacitive array successive comparison type, and frequency-to-voltage conversion type.

Main performance indicators:

1) Resolution: Resolution mainly indicates the precision information, usually expressed in bits. For example, if a stick is divided into 10 parts and 100 parts, it is obvious that the one divided into 100 parts is more detailed. Similarly, the higher the ADC resolution, the higher the precision, allowing for finer details to be observed.

2) Conversion Rate: This refers to the reciprocal of the time required to complete one conversion from an analog signal to a digital signal. There is also a concept of Sampling Rate, which refers to the interval between two conversions. Typically, the sampling rate should be less than or equal to the conversion rate. This is easy to understand; we must wait for the analog signal to be converted to a digital signal before sampling it, otherwise the sampled data would be meaningless.

3) Quantizing Error: This is the error caused by the finite resolution of the ADC.

4) Offset Error: The value of the output signal when the input signal is zero is not zero; this can be adjusted using an external potentiometer.

There are many more actual indicators, but here we only introduce a few to give everyone a basic concept. If you want to study ADC indicators in depth, you can refer to some ADC device manuals, which provide detailed information.

2 Classification and Performance Indicators of DAC

DACs are usually classified into voltage output type, current output type, multiplying type, and single-bit DA converters.

Main indicators:

1) Resolution refers to the ratio of the minimum analog output to the maximum.

2) Setting Time is the time required to convert a digital quantity into a stable analog quantity.

3 Conclusion

Currently, the development of embedded systems revolves around core processors such as microcontrollers and FPGAs (what microcontrollers and FPGAs are will be introduced in a dedicated article later). Both are digital chips that process digital signals. Typically, embedded systems are designed to solve specific problems, such as a thermometer, which needs to convert the physical signal of human body temperature into a digital signal in voltage form for the core control device to process. Therefore, an ADC is required for this conversion from physical signal to digital signal in voltage form. To be precise, a sensor is needed to convert the physical signal of temperature into an analog signal in voltage form, and then an ADC is required to convert the analog signal into a digital signal. Understanding what ADC does is sufficient; specific parameter details do not need to be deeply researched, as I will explain them in detail when they are used later. Similarly, the role of DAC is similar; when the core processor needs to drive actual physical devices, it must convert digital signals into analog signals because actual physical devices can only understand analog signals. DAC is responsible for completing the conversion from digital to analog.