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Reducing Noise in Gain & Phase Measurement of DC-DC Converter's Control Loop
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T3sl4co1l:
Classic appearance of common mode noise.  Connect the ground near where the signals come from, then make a common mode transformer by carrying one extra ground wire with the bundle of wires, through a suitable core, back to the main ground pin where the power wires connect.  The ground loop voltage through the extra wire (which would ordinarily be a shorted turn, but that ignores the fact that ground isn't, in fact, ground, everywhere on the board) induces a similar voltage in all the other signals, keeping them quiet(er).

Maybe.

Use a few turns on a large ferrite, usually a clip-on cable clamp style, but a toroid (ferrite, not powdered iron -- if it's not dark gray, and you don't know what it came from, assume it's not) will do fine, just a little inconvenient to loop your wires through.

Tim
bendras:

--- Quote from: KIKi on October 23, 2018, 07:19:41 am ---Did you try soldering GND wire on the bottom layer (put GND wire on other side of the PCB)? You should move GND wire as far as you can from the SW pin (inductor).

--- End quote ---

I  have tried this out (please see pictures below) and it seems to have reduced noise quite a bit  :-+.
bendras:

--- Quote from: capt bullshot on October 23, 2018, 07:33:40 am ---The probing technique looks quite inappropriate.
You should use the usual grounding method for the scope probes: Remove the ground clip, connect the probe GND directly to the circuit boards GND plane and the probe tip as short as possible to the measurement points.
Often done by winding a short piece of stiff wire around the GND sleeve and soldering that to the GND plane while pointing the tip to the test point. That should reduce the coupled switching noise significantly.

--- End quote ---

I have tried this out as well (please see pictures below) and it seems to have also reduced the noise quite a bit  :-+.
bendras:

--- Quote from: T3sl4co1l on October 24, 2018, 02:25:58 pm ---Classic appearance of common mode noise.  Connect the ground near where the signals come from, then make a common mode transformer by carrying one extra ground wire with the bundle of wires, through a suitable core, back to the main ground pin where the power wires connect.  The ground loop voltage through the extra wire (which would ordinarily be a shorted turn, but that ignores the fact that ground isn't, in fact, ground, everywhere on the board) induces a similar voltage in all the other signals, keeping them quiet(er).

Maybe.

Use a few turns on a large ferrite, usually a clip-on cable clamp style, but a toroid (ferrite, not powdered iron -- if it's not dark gray, and you don't know what it came from, assume it's not) will do fine, just a little inconvenient to loop your wires through.

Tim

--- End quote ---

At the moment I do not have a ferrite core handy, but I will get one and report the findings  :)
bendras:

--- Quote from: bendras on October 24, 2018, 06:57:52 pm ---
--- Quote from: T3sl4co1l on October 24, 2018, 02:25:58 pm ---Classic appearance of common mode noise.  Connect the ground near where the signals come from, then make a common mode transformer by carrying one extra ground wire with the bundle of wires, through a suitable core, back to the main ground pin where the power wires connect.  The ground loop voltage through the extra wire (which would ordinarily be a shorted turn, but that ignores the fact that ground isn't, in fact, ground, everywhere on the board) induces a similar voltage in all the other signals, keeping them quiet(er).

Maybe.

Use a few turns on a large ferrite, usually a clip-on cable clamp style, but a toroid (ferrite, not powdered iron -- if it's not dark gray, and you don't know what it came from, assume it's not) will do fine, just a little inconvenient to loop your wires through.

Tim

--- End quote ---

At the moment I do not have a ferrite core handy, but I will get one and report the findings  :)

--- End quote ---

I have tried out the common mode transformer suggestion and it seems that this has reduced the noise a tad in comparison with the other methods  :). See the images attached below.
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