Noise of 0 ohm resistor?

[pstamler]

What does Ohm's law tell us about VOLTAGE noise across ZERO ohms?

Well, of course. But the question here is what the real resistance of these "0 ohm" resistors is, and what significance that might have. After all, there's nothing that has 0 ohms in the real world except superconductors.

Peace,
Paul

 

[emrr]

And my dumb question would be, at a critical impedance and frequency, what differences exist between using 0 ohm parts versus using bits of jumper wire?  Not operating in this field at all, my assumption from the outside would be that straight wire would be better compositionally.  But then, is that even possible with machine fabricated boards, or are you stuck with having to use easily insertable 0 ohm parts? 

 

[Svart]

I'm stuck using machine placed parts.  Realistically if the bits of wire could be manufactured in a repeatable manner and their tolerances don't change much and they could be machine placed then they would be a little more desirable functionally but realistically you'd have issues with solder creep and being able to guarantee they don't roll around or get placed crooked/offset and so forth.  Those types of issues can be worse than having a discontinuity in a transmission line like a SMD 0 ohm jumper because they can be random.  I'd rather have a repeatable problem than one that is random any day of the week.

 

[sahib]

There are about 30 of them in the signal path which is a 50ohm transmission line.  

According to the type of zero ohm links I am using you have approximately 0.15 ohms in total.

I just did a rough calculation. If I am wrong my masters could correct me. 0.25mm diameter x 10mm length copper wire would present a resistance of 0.0034 ohm. Therefore if you had copper jumpers instead of these links (which are also wires) that would give you 0.102 ohm in total. Not much of an improvement, plus you have the headache of insertion problems. So, just as well you are not allow to change the PCB because you would be worse off as thinner cross section of a track would give you much higher resistance. Unless, of course you are able to shorten the overall length of the line. Hence, my crude mathematic tells me that this is not the area that you should be concerned.

Edit. If you replaced these copper jumpers with silver wires the total resistance would be around 0.095 ohm.

 

[Svart]

Yeah I agree, that I wouldn't get much benefit from it other than slightly lower resistance.  The greater amount of solder needed to surround the diameter of the wire might add more resistance too since solder is not quite as good of a conductor as copper.

 

[CJ]

opened up this wifi box
has tuned traces all over the input

playing games with intentional caps due to traces being close, or on top of each other,
then a 1 meg resistor across the + and = signal traces, then more traces, another resistor,
so if you can get your signal to resonate down the line, maybe your s/n ratio will get better.

 

[Svart]

that type of stuff is tuning the transmission lines.