“This article introduces in detail the difference between the common ground and the non-common ground of the analog circuit and the digital circuit in the PCB board. In order for everyone to understand… I drew two circuits with ORCAD, one is an ordinary triode analog amplifier circuit, and the other is a digital circuit oscillator.

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This article introduces in detail the difference between the common ground and the non-common ground of the analog circuit and the digital circuit in the PCB board.

In order for everyone to understand… I drew two circuits with ORCAD, one is an ordinary triode analog amplifier circuit, and the other is a digital circuit oscillator.

Below is the circuit diagram of the two circuits when one point is grounded

In fact, there is no need to draw a point ground like this in the schematic diagram, just for everyone to see it more clearly. . As you can see, the left is an ordinary amplifier circuit, and the right is an oscillator. Because the current in the digital circuit part is too small during the simulation, a first-level triode is connected behind it.

Below are the waveforms of the two circuits:

You can see that both waveforms are very good with no distortion.

The red one is the waveform when the triode amplifier is amplified, and the green one is the oscillator waveform. Some people may ask why the red one does not work in the previous waveform? That’s because the actual power supply is simulated in ORCAD, and there is a period of time from no power to when there is power, so the previous waveform is very small.

You can see that there is a little grounding, the two circuits have no effect, and they work normally with each other. Related articles are recommended: Recognize ground bounce (ground noise).

The following is not the circuit diagram when one point is grounded

Here, two resistors are used to replace the resistance of the wiring on the PCB. Some people will definitely say that this is not a piece of shit. How can the resistance on the PCB be so big. 50 euros…haha!

Here I use such a large size for everyone to see it more intuitively. In fact, it will not be so large, but for circuits with high frequencies, sometimes the impedance of the wire is much smaller than the inductive reactance! ! ! That may produce such a large resistance, here is the digital circuit connected to the back.

The following are the simulation waveforms of the two circuits. Will there be no interference as before?

You can see that the waveform amplification of the analog circuit is disturbed and it is not good.

Send a separate analog waveform, as follows.

This distortion is appalling.

The numbers below are distributed, because the numbers are placed close to the power supply, the interference is not very serious.

You can see that the digital circuit is still disturbed.

I will post an enlarged picture for everyone to see, as follows.

You can see, is it disturbed by simulation?