Summary of basic knowledge of analog and digital circuits

As a hardware engineer, you must face two basic circuits: analog circuits and digital circuits. Let's take a look at the basic knowledge of these two circuits.

Definition and characteristics of analog circuits and digital circuits:

Analog circuits (electronic circuits)

Electronic circuits that process analog signals. The word "analog" mainly refers to the proportional reproduction of voltage (or current) to the real signal.

Its main features are:

1. The function has infinite values;

2. When the image information and sound information change, the waveform of the signal also changes, that is, the information to be transmitted by the analog signal is contained in its waveform (the information change rule is directly reflected in the changes in the amplitude, frequency and phase of the analog signal) .

3. The primary analog circuit mainly solves two major aspects: 1. amplification and 2. signal source.

4. The analog signal has continuity.

Digital circuits (circuits that perform arithmetic and logical operations)

A circuit that uses digital signals to perform arithmetic and logical operations on digital quantities is called a digital circuit, or digital system. Because it has logical operations and logic processing functions, it is also called a digital logic circuit.

Its main features are:

1. It has both arithmetic and logical operation functions.

Digital circuits are based on binary logic algebra and use binary digital signals to perform both arithmetic operations and logical operations (AND, OR, NOT, judgment, comparison, processing, etc.). Therefore, they are extremely suitable for operations and comparisons. , storage, transmission, control, decision-making and other applications.

2. Simple implementation and reliable system

Digital logic circuits based on binary systems have strong reliability. Small fluctuations in the power supply voltage have no impact on it, and temperature and process deviations have much less impact on the reliability of its operation than analog circuits.

3. High integration and easy function implementation

High integration, small size and low power consumption are one of the outstanding advantages of digital circuits. The design, repair and maintenance of circuits are flexible and convenient. With the rapid development of integrated circuit technology, digital logic circuits are becoming more and more integrated. The functions of integrated circuit blocks have changed with the functions of small-scale integrated circuits (SSI) and medium-scale integrated circuits (medium-scale integrated circuits). The development of MSI), large-scale integrated circuits (LSI), and very large-scale integrated circuits (VLSI) has also risen from component level, device level, component level, board level to system level. The design of the circuit only requires the connection of some standard integrated circuit block units. For non-standard special circuits, programmable logic array circuits can also be used to achieve arbitrary logic functions through programming.

2. The difference between analog circuits and digital circuits

Analog circuits are circuits that process analog signals; digital circuits are circuits that process digital signals.

Analog signals are functions of time and are a continuously changing quantity, while digital signals are discrete quantities. Because all electronic systems are based on specific electronic devices and electronic circuits, in a signal processing, signal collection and signal recovery are all analog signals, and only the middle part of the signal processing is digital processing. Specifically, analog circuits mainly process analog signals, signals that do not change with time and are continuous in both time domain and value domain, such as speech signals. Digital signals, on the contrary, change. Digital signal processing includes signal sampling, signal quantization, and signal encoding.

To give a simple example: If you want to transmit a sound that changes from small to louder from a distance, and use amplitude modulation or analog signals to transmit it (correspondingly, analog circuits should be used), then the amplitude of the signal during the transmission process will become larger and larger. Large, because it uses the amplitude characteristics of the electrical signal to simulate the strength characteristics of the sound.

However, if digital signal transmission is used, a kind of encoding must be used. Each level of sound size corresponds to a encoding. At the sound input end, every time a sample is taken, the corresponding encoding is transmitted. It can be seen that no matter how many levels the sound is divided into, no matter how high the sampling frequency is, there is still a loss in this method for the original sound. However, this loss can be compensated by increasing the sampling frequency. In theory, the sampling frequency can be completely restored if it is greater than twice the frequency of the original signal.

The levels of digital circuits are all in compliance with standards, while analog circuits do not have such requirements.

3. The connection between analog circuits and digital circuits

Analog circuits provide power to digital circuits and complete the execution of actuators.

In analog circuits and digital circuits, signals are expressed differently. Operations that can be performed on analog signals, such as amplification, filtering, limiting, etc., can also be performed on digital signals. In fact, all digital circuits are fundamentally analog circuits, and their basic electrical principles are the same as analog circuits. Complementary metal oxide semiconductor is composed of two analog metal oxide field effect transistors. Its symmetrical and complementary structure allows it to handle high and low digital logic levels. However, digital circuits are designed to process digital signals, and if any analog signal is forcibly introduced without additional processing, quantization noise may result.

A function that represents the value of a signal at a discrete set of times is called a discrete-time signal. Because the most commonly encountered discrete-time signals are analog signals sampled at even (and sometimes non-uniform) intervals in time. "Discrete time" and "digital" are often used to describe the same signal. Some theories of discrete-time signals also apply to digital signals.

4. How to realize the functions of analog and digital circuits

Analog circuits and digital circuits are also carriers of signal changes. In analog circuits, the amplification and reduction of signals in the circuit are achieved through the amplification characteristics of components, while in digital circuits, the transmission of signals is achieved through switching characteristics. operational.

In analog circuits, the changes in voltage, current, frequency, and period are mutually restricted, while in digital circuits, the changes in voltage, current, frequency, and period are discrete.

Analog circuits can work under large currents and high voltages, while digital circuits only work under small voltages and low currents with low power consumption to complete or generate stable control signals.

5. Application

Analog circuits cover almost the entire electronic field, and the functional realization of any electronic circuit will involve analog circuits.

Digital circuits and digital electronic technology are widely used in scientific and technological fields such as television, radar, communications, electronic computers, automatic control, and aerospace.

The design of analog circuits is usually more difficult than digital circuits and requires higher levels of designers. This is one of the reasons why digital circuit systems are more popular than analog circuit systems. Analog circuits generally require more manual calculations, and their design process is less automated than digital circuits.