capacitance between two long traces in PCB

Thread Starter

Pradeepraj

Joined Nov 29, 2023
2
1701252064375.png

We are having coil which is connected to white color trace. One pink color trace is placed parallel near the coil trace and connected to one end of the resistor. Is any current induce to pink color trace because of coil energizing in white trace. Please explain.
 

MisterBill2

Joined Jan 23, 2018
17,729
There will be some voltage induced into the portion of the pink trace by the changing magnetic field from current in the white trace. BUT that induced voltage may not be great enough to measure with common equipment. The voltage induced will be quite low. It is not likely that the voltage induced by a capacitive effect will be very easy to measure, either.
 

Janis59

Joined Aug 21, 2017
1,813
I would guess to measure it by means of VNA is much easier as to calculate, and even more strictly about accuracy. VNA can measure with an ease the 0.1 pF and less, whilst the calculus must take in consideration the area looking affront each other in that 30 micron path thickness multiplied to pchb material epsilon (which may be rather different even in single pcb platelet and never is known exactly) and add the side area effect which are not nokking each on other but still gives some leakage field lines therefore capacitance, take in consideration the capacitor line shortness (leakage) what may blow the results away sometimes even with factor of so large as 5. Thus, my advice - never trust in calculus but only fresh measurement data.
 

Thread Starter

Pradeepraj

Joined Nov 29, 2023
2
There will be some voltage induced into the portion of the pink trace by the changing magnetic field from current in the white trace. BUT that induced voltage may not be great enough to measure with common equipment. The voltage induced will be quite low. It is not likely that the voltage induced by a capacitive effect will be very easy to measure, either.
Hi Bill,
How can we give give input to coil it has zero impedance so I can,t able to give DC supply. I gave AC source across the coil checked whether any voltage is induced across the resistor but there no voltage across that. Pink trace is non inverting input given to op-amp.
 

MisterBill2

Joined Jan 23, 2018
17,729
Unless the input coil is a "superconductor" by the standard definition, it has some resistance and some inductance, although those values may be below the resolution of the measurement system in use. (That is to say, just because you can not see it does not mean it is not there.) And definitely current can flow through the heavy white trace, although any voltage developed is below what the present system can measure. So certainly the changing current will produce a magnetic field that will induce a voltage into the pink trace.
So the various voltages may be less than the ability of the measurement system, which certainly happens.
The result may then be that although they are there, they do not matter. THAT is many times the case in real world engineering. Of course that is the happy result: The interference is reduced to an amount that does not matter. THAT counts as success in the real world.
 

Janis59

Joined Aug 21, 2017
1,813
RE: Bill <<although those values may be below the resolution of the measurement system in use.>>
Very much disagee. The values 0.01-0.1 pF and 1...10 nH are well in the range of sensitivity of even average heap VNA capabilities. That was in my young days 65 years ago when 10 pF and 1 microHenry was something on the edge.
 

drjohsmith

Joined Dec 13, 2021
850
Hi Bill,
How can we give give input to coil it has zero impedance so I can,t able to give DC supply. I gave AC source across the coil checked whether any voltage is induced across the resistor but there no voltage across that. Pink trace is non inverting input given to op-amp.
Any two adjacent conductors , carrying a current will couple .
It's the basis of how a transformer works !
how much coupling depends upon the length and distance apart, the frequency and the current flowing and the voltage.
This might be of use,
https://www.protoexpress.com/blog/crosstalk-high-speed-pcb-design/
What an engineer needs to decide is, is there significant enough coupling to cause a problem, and if so mitigate,
As you see, moving apart, lowering voltage or current or frequency are first options, putting a shield between is a second approach,
 
Top