Overview of analog circuits
The analog circuit refers to a circuit used to transmit, transform, process, amplify, measure, and display analog signals (referred to as continuously changing electrical signals). It is the foundation of electronic circuits, mainly including amplifier circuits, signal operation and processing circuits, oscillation circuits, modulation and demodulation circuits, and power supplies. Whether learning hardware design or high-speed PCB design, analog circuits are essential knowledge that everyone needs to master.
Analog electronics itself is a very complex subject, and analog electronics courses are just the most basic of them. Analog circuit (Analog Circuit) means an electronic circuit that processes analog signals. Most signals in nature are analog signals, and they have continuous amplitude values, such as voice signals when speaking.
The analog circuit can directly process such signals (of course, it needs to be converted into electrical signals first). For example, the power amplifier can amplify the sound signal, and the broadcast station can send the simulated sound signal and image signal. It can even be considered that all circuits are based on analog circuits (even if they are digital circuits, the underlying principles are also based on analog circuits). Its importance is self-evident. Due to the rapid development of digital circuits and programmable devices, it embodies many superior characteristics. Many electronic devices are slowly digitized, but analog circuits are still inseparable.
At present, the most important devices in analog circuits are none other than semiconductor devices. The most basic and commonly used semiconductor devices are diodes, transistors, field effect transistors and operational amplifiers. Diodes have many functions. For example, ordinary diodes can be used for rectification, light-emitting diodes can be used for indicator lights and lighting, voltage regulators can be used for voltage regulation, and varactor diodes can be used for signal modulation. In the analog electronics course, the part involving the diode is relatively simple, and many characteristics of the field effect tube are similar to the triode, so the triode or op amp is often used as the main explanation.
The difference between analog and digital circuits
Analog circuits are circuits that process analog signals; digital circuits are circuits that process digital signals.
The analog signal is a function of time, which is a continuously changing quantity, and the digital signal is a discrete quantity. Because all electronic systems are based on specific electronic devices and electronic circuits. In a signal processing, signal acquisition and signal recovery are analog signals, and only the middle part of the signal processing is digital processing. Specifically, the analog circuit mainly processes analog signals, and does not change with time. Both continuous signals in the time domain and value domain, such as voice signals. Digital signals, on the other hand, change. The processing of digital signals includes signal sampling, signal quantization, and signal encoding.
▶ A simple example:
If you want to transmit a sound that changes from small to large from a distance, use amplitude modulation and analog signals for transmission (the corresponding analog circuit should be used), then the amplitude of the signal during transmission will become larger and larger, because it is in Use the amplitude characteristics of electrical signals to simulate the strength and weakness of sound.
However, if digital signal transmission is used, a code must be used. Each level of sound size corresponds to a code. At the sound input terminal, each time a sample is taken, the corresponding code is transmitted. It can be seen that no matter how much the sound is classified, no matter how high the sampling frequency is, for the original sound, there is still a loss in this way. However, this loss can be compensated by increasing the sampling frequency. In theory, the sampling frequency is greater than twice the frequency of the original signal and can be completely restored.
The levels of digital circuits are in compliance with standards, and analog circuits have no such requirements.
In our actual circuit design, it is often necessary to combine analog circuits with digital circuits. There are both analog signals and digital signals as shown below:
