In PCB layout design, the most common technology is the circuit board grounding, from the most common single analog circuit loop grounding, simple digital circuit loop grounding to analog digital circuit hybrid grounding, from these grounding methods all show the development of electronic design. If the product you design has other requirements, for example, after EMC testing, the signal frequency of the circuit board is relatively high (the rise time of the signal is 10ns or even lower), then the grounding technology that needs to be considered should also meet the factors at this time. So, today we will analyze and explain the grounding technology under these factors.
Before analyzing the grounding technology of circuit board, we should first understand one reason. Grounding technology is one of the factors to improve the stability of circuit. In the circuit design, reducing the loop through various grounding technologies is one of the methods. Now let’s talk about the technology to reduce the impact of the ground loop.
A uses optocoupler technology to connect the circuit
In the design of circuit, in order to fully protect the latter circuit from the influence of the former circuit, optocoupler isolation technology is one of the common methods
In this design, the influence of the transmitting circuit on the receiving circuit can be well reduced. It is because of the introduction of the optocoupler that the influence of the ground loop on the circuit is greatly reduced.
B use isolation transformer technology to connect the circuit
In this method, a 1:1 transformer is used to isolate the transmitting circuit and the receiving circuit. The ground circuit of receiving circuit is greatly reduced.
C adopts common mode choke
In the circuit design, the receiving circuit is connected with the transmitting circuit through the common mode choke, which can greatly reduce the loop of the receiving circuit and provide good technical support for the EMC detection of the receiving circuit.
D uses balanced circuit technology
In this method, the transmitting circuit is usually a multi-point parallel power supply, through each module circuit equivalent to parallel connection, and finally each module in parallel connection is connected to a single point grounding. In the balance circuit, the current flow of each module does not affect each other, so as to improve the stability of the system.
After introducing the methods of reducing the ground loop, now we will introduce the grounding methods in order to reduce all kinds of grounding.
1、 Floating technology
In electronic design, floating ground technology is a common method. The signal ground of the circuit board is not connected with the external common ground, so as to ensure the good isolation of the circuit. The circuit is well isolated from the external grounding system, and is not easy to be affected by the interference from the external grounding system. However, it is easy to accumulate static electricity on the circuit, resulting in electrostatic interference, which may produce dangerous voltage.
Small low speed (< 1MHz) equipment can adopt floating working ground (or working ground single point to metal shell) and metal shell single point to earth,
2、 Series single point grounding
This kind of grounding method is a kind of grounding method recommended by Daniel of the company. Because of its simplicity, it does not need to pay attention to so much in the circuit board design, so it will be used more. However, this kind of circuit is easy to have common impedance coupling, which makes each circuit module influence each other.
3、 Parallel single point grounding
Although this grounding method gets rid of the problem of common impedance coupling of series single point grounding, in actual use, it will introduce too many troubles of grounding wire. As for which method to use, it needs to be comprehensively evaluated in the actual process. If the area of the circuit board allows, the parallel mode is used. If the connection between each circuit module is simple, the series mode is used. Generally, there are power supply module, analog circuit module, digital circuit module and protection circuit module in the downloaded board. In this case, I use the method of parallel single point grounding.
4、 Multipoint grounding
Multipoint base technology will be used more in daily design, and more in multi module circuit design. This grounding method can effectively reduce the problem of high frequency interference, but it is also easy to produce the design problem of ground loop, which should be fully considered in the design to improve the stability of system design. The working ground of small high-speed (> 10MHz) equipment should be multi-point grounded with its metal shell, the distance between the grounding points should be less than 1 / 20 of the wavelength of the highest working frequency, and the metal shell should be single point grounded.
In short, in the electronic circuit design, the most important point is to reduce the circuit area, which plays an important role in improving the stability of electronic design and improving the EMC design of electronic system. In the actual design, through the comprehensive evaluation of the above technologies, through flexible use, in order to achieve the purpose of improving the stability of the system.