Reducing Ground Noise

Thread Starter

PIC-User

Joined Sep 25, 2015
78
I have a very noisy ground plane that I'm trying to clean up a little bit. Below there is a picture of the changes that I have made to reduce the noise. There are two connectors in the circuit a USB (U41) and a mono connector (U142). I added three caps between the input voltage (5V) and the ground plane shown in blue. Bright blue corresponds to the top layer and dark blue is the bottom layer. Any extra noise that I could clean up is going to help me a lot with this circuit. I was getting a lot of ground noise going out through the U142 connector before making these changes. Putting a 1k series resistor in U142 helps a little bit.

I understand that there might be ground loop issues in other parts of the circuit. I have already identified some ground path/loop issues and I have fixed them.

If you have any comments or suggestions on how to improve the noise level in this circuit, I will really appreciate it. Any components I could use? I was thinking about adding Tantalum caps, but I have read that they have a tendency to explode. I'm not sure about that. Any help is greatly appreciated. Thanks.

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KeithWalker

Joined Jul 10, 2017
3,188
How do you know that it is a noisy ground plane? What part of the circuit are you using for a reference for your measurements?
The problem much more likely to be a noisy power supply or pick-up from a radiated EM noise source.
 

Thread Starter

PIC-User

Joined Sep 25, 2015
78
How do you know that it is a noisy ground plane? What part of the circuit are you using for a reference for your measurements?
The problem much more likely to be a noisy power supply or pick-up from a radiated EM noise source.
I am using an oscilloscope at the output of connector U142. I'm sure that the improvements I did will clean the noise up by a lot, but I was looking for a second opinion from you guys. I have an RFID module in this circuit. That's where the noise is comming from.
 

MisterBill2

Joined Jan 23, 2018
19,474
OK, so instead, here is a description of what usually works to reduce conducted noise from a segment of a circuit: First, a capacitor across the power connections to that segment. The value should be high enough to have a low impedance at the predominant noise frequency. Then, in addition, an adequately capable series inductance between that power input and the power source. This would be best if it were a bifilar filter inductor so that it will tend to block noise on both the supply and the return sides of the power feed. Next, another shunt capacitor across the supply connections on the power source side of the filter inductance.
In addition, if there are signal or control connections that have shielded wires, those shields should only be terminated at one end of the conductor, usually the end outside of the noisy segment.
The capacitors must have a voltage rating greater than the sum of the power supply voltage and the magnitude of the noise signal.
 
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