What is the 0 ohm resistance in the circuit?

Preface

This digest is self-aware. Question 0: Why can we separate the ground in a digital analog hybrid circuit? Some of my answers have not been approved by anyone before. If there is any infringement, please contact the blogger's email to delete it. Thank you.

@ Operation amplifier answer

The following is the original article: @ magic sub's answer is inaccurate for the following reasons:
First, 0 euro resistance is not convenient for debugging. I have never broken the connection between analog and digital places during circuit adjustment. This is not called debugging. This is called intentional board burning.

Second, 0 euro resistance can be used as a wire, but it cannot be equivalent to a wire. This is exactly what Shi Wei said. For the signal, the impedance of 0 euro resistance is not zero.

Third, the ground line can be split. This is completely correct. It depends on the signal characteristics. However, EMC is not a profound theory. The two principles can be summarized.

Some people say that the separation of land is useless, or the use is not obvious. I can only say that the division of land in your application is of little use, or that the principle and essence of the Division are not understood during the division, therefore, the effect of separation is better than that of separation. Free to play 0.5 uvpp 10 MHz signal amplification 80 dB gain circuit, teach you how to behave in minutes, teach you what is EMS and EMI, what is the waveform rotten to the oscilloscope can not recognize the signal.

The following are private EMC, that is, electromagnetic compatibility. When designing a circuit, the general EMC problem is divided into two specific problems:

1. Impedance Matching

2. grounding and shielding.

The subject's problem is grounding. Today we will talk about grounding.

First, what is grounding?

Grounding-provides a zero potential reference plane for a circuit or system to establish a low impedance path between the system and the ground. In a circuit, there are two types of signals that require backflow: Signal and interference.

To ensure that the circuit works properly, you must ensure that the signal is clean and not affected by interference (grounding and shielding). Of course, you must not be affected by yourself (impedance matching ).

After understanding the basic point of the circuit, let's talk about the concept of signal reflux. Let's take a look at the two figures below. The figure is found in the forum. If there is any improper situation, notify me to delete it. The first one is the comparison of the reflux paths of different signals. The blue is the ground plane, and the red is the signal line. We can see that 1 kHz and kHz are reflux through the whole ground plane, while the 1 MHz signal, reflux is under the signal line. The second and third images are enlarged.

As you can see, the signal reflux path varies greatly with the signal frequency. Here is an extremely important concept: skin effect. To put it bluntly, the signal will automatically select a low-impedance loop for backflow.

When the frequency is low, the loop impedance of the whole ground plane is not obvious, so the signal will flow back through the whole ground plane. However, when the signal frequency increases gradually, the ground impedance effect will be reflected, at this time, the signal will automatically select the edge of the signal line for propagation, select the ground loop next to the signal line for reflux. This is also the reason why the audio circuit is not laid out in a large area and is grounded at a single point. The circuit of 1mhz-10mhz must be grounded at a single point and ensure the integrity of the ground plane as much as possible. The RF circuit often connects the ground to a ring. No matter whether it is a signal or interference, it follows the principle of where it comes from and where it goes back. Therefore, no matter how the ground line is processed, it will improve the interference reflux Impedance On the signal reflux path as much as possible, let the interference select a completely different path from the signal reflux path for reflux.

To sum up the 0-euro resistance mentioned by the subject (in fact, 0-euro resistance is actually used in a small signal digital-to-analog hybrid circuit to separate signals, in most cases, the iron magnet is used when the ground is split. The function is to improve the impedance of the noise signal on the signal reflux path. In addition, we often use a digital-analog hybrid circuit below 10 MHz instead of separating digits from analog ones with 0-euro resistance, instead, we choose to apply 0 euro resistance or iron magnet to the power source ground, because at this time, only the power supply can be regarded as "clean ", both the analog and digital locations are noisy. The following figure shows a total of five locations, namely, signal, analog, digital, power, and clock.

@ Xiaowen's answer

Please do not come here. @ magic and @ operational amplifier have already talked about several key points and analyzed them well. I will not go into details here if there is a picture of the truth;

I also give a concise list of some 0 ohm resistance usage based on the actual situation I encountered during my work:

1. It does not play a practical role in the circuit. It only works on the PCB for convenience of debugging or Electromagnetic Compatibility Design.

2. When the Jumper works, if a line does not need to be used, directly do not solder the resistor.

3. When the matching circuit parameters are uncertain, use 0 ohm instead. In actual debugging, determine the parameters and replace them with specific resistance values.

4. When you want to test the current of a line, you can remove the 0 ohm resistance and connect it to the current meter to facilitate the test.

5. If layout is unavailable, you can add a 0 ohm resistor (not recommended)

6. In a high-frequency signal circuit, when the inductance or capacitor. Solve EMC problems.

7. Single Point Grounding

8. Fuse

9. Single Point Grounding in analog and digital locations

10. Sometimes there may be no jumper or dial switch on the product. Sometimes the customer may be cheap and cause an error. It can be replaced by 0 Euro.

@ MKO's answer

0 ohm resistance is not used to separate numbers from analog ones, but to enable electrical connections between analog and digital places, because analog and digital places belong to the same network after all, eventually, they still need to be connected together. Separating digital models is just a means for engineers to solve interference.

The convenience of using 0 ohm resistance is that it is easy to disassemble, and can be replaced by another device to observe the final effect for comparison, while the wire cannot be disassembled. In fact, the idea of Throttling is not quite consistent. 0 ohm resistance has an impedance but is small after all. How large is the current flow to throttling? What? Unrealistic. Many circuit boards cannot reach this current level. On the contrary, there is a great impact on the impedance. If the 0-euro resistance impedance is large, the common mode interference caused by the voltage drop on the 0 ohm cannot be ignored.

The isolation between digital and simulated locations is actually a technical task and belongs to the EMC category. I do not agree with some engineers who say that as long as it is a digital-analog hybrid circuit, it is necessary to split the digital ground and analog ground, and then connect it with a magnetic bead or 0 ohm resistor. You must analyze the specific problem. I have seen a lot of circuit boards that adopt a unified, that is, an incorrect division. Of course, there is no problem of connecting with 0 euro resistance. Its EMC can do well.

Instead, some use ground-separated circuit boards, EMC is poor. The reason for this is the engineer's misunderstanding of the nature of EMC. In fact, the key point of EMC is to minimize the circulation path. If the circulation path is divided, it should be noted that once the signal line crosses the geographic line, the circulation path will inevitably increase and EMC performance will deteriorate. The layout of a unified circuit board must be fully considered in advance, and the circuit module should be physically partitioned (not separated) to ensure that all modules have their own circuits, so that other modules will not be affected, at the same time, because the ground is not separated, the integrity of the ground is guaranteed. Of course there are too many details, so we will not discuss them one by one.

Segmentation is good, and it can indeed achieve better digital-analog isolation, but without division, EMC is not necessarily bad. There is no such thing as absolute. No such thing is absolutely good, but it should be decided based on the specific situation, rather than separated, for EMC performance. Separation is just a means, there are multiple methods. Then, let's analyze the specific problem. The above (may be incorrect)

Conclusion

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What is the 0 ohm resistance in the circuit?