[SI-LIST] Re: Effect of contact resistance on high frequency signals
- From: boris.traa@xxxxxxxxxxx
- Date: Wed, 13 Nov 2002 11:16:04 +0100
Kind regards
Boris Traa
System design engineer EMC
Philips Semiconductors BV, dep. SLE
Location A320/301
PObox 80021, 5600JZ
Eindhoven, The Netherlands
Tel: ++ 31 40 27 22249
Fax: ++ 31 40 27 23238
E-mail: boris.traa@xxxxxxxxxxxx Seri: btraa@nlsce1
----- Forwarded by Boris Traa/EHV/SC/PHILIPS on 13-11-2002 11:16 -----
Boris Traa
To:
KaiKeskinen@xxxxxxxxxxxxx
13-11-2002 11:15 cc:
Subject: Re: [SI-LIST]
Effect of contact resistance on high frequency signals(Document link: Boris
Traa)
Classification:
Unclassified
Pushing pieces of metal tightly together (e.g. a metal shield contact finger
and a PCB copper pad) always lead to a lower EMI reduction than a few soldered
contacts. Until now I could not find an explanation. It is just like contact
potentials are
generated due to a contact between 2 different materials (iron and copper) and
as such a kind threshold voltage is present that has to be exceeded before
conductioncan start. An electric DC motor also suffers from these contact
potentials at the rotor
contacts. This transition acts as a diode.
So I'm also very eager to understand the mystery of contact resistance.
Kind regards
Boris Traa
System design engineer EMC
Philips Semiconductors BV, dep. SLE
Location A320/301
PObox 80021, 5600JZ
Eindhoven, The Netherlands
Tel: ++ 31 40 27 22249
Fax: ++ 31 40 27 23238
E-mail: boris.traa@xxxxxxxxxxxx Seri: btraa@nlsce1
"Keskinen, Kai"
<KaiKeskinen@sole To: si-list
<si-list@xxxxxxxxxxxxx>
ctron.com> cc: (bcc: Boris
Traa/EHV/SC/PHILIPS)
Sent by: Subject: [SI-LIST] Effect
of contact resistance on high frequency signals
si-list-bounce@fr
eelists.org Classification:
12-11-2002 20:09
Please respond to
KaiKeskinen
Does anyone out there have any links or papers related to the effect of
degrading contact resistance on high frequency signals (i.e. 622Mbps and
above)?
All the info I can dig up on contact resistance is basically at DC.
What happens to your high speed signals when all the gold has been scraped
off the board or backplane connector pin on the 201st or 400th or 1000th
insertion?
Thanks,
Kai Keskinen
Signal Integrity Advisor
Solectron Technical Center
425 Legget Drive,
Kanata, ON K2K 2W2
kaikeskinen@xxxxxxxxxxxxx
www.solectron.com
> "This message may contain information proprietary to Solectron so any
unauthorized disclosure, copying or distribution of its contents is strictly
prohibited."
-----Original Message-----
From: Mike Brown [mailto:bmgman@xxxxxxxxxx]
Sent: Tuesday, November 12, 2002 9:12 AM
To: zhang_kun@xxxxxxxxxx
Cc: si-list
Subject: [SI-LIST] Re: Decoupling of Oscillator
Zhangkun,
You are right - that filter network is not to keep the oscillator
spectrum out of the power supply, but to keep power supply noise from
modulating the oscillator. Jitter will be introduced into the system
timing if this modulation occurs. Some jitter will unavoidably occur
but the filter, including the tantalum cap, will minimize the amplitude.
The noise frequency will be determined by the timing of the loops in
the software, which change the power loading periodically. Any load
variation above the regulator cutoff frequency is a possible noise source.
I prefer to isolate the power to the oscillator. Others don't, and they
get away with it if their system is not jitter sensitive. I once built
a system with two oscillators and no isolation and found the resulting
jitter due to the asynchronous noise to be intolerable. Isolation
solved the problem.
Regards,
Mike
Zhangkun wrote:
>Hi all
>
>I meet one question about decoupling of oscillator. In our design, the
power supply of OSC is always isolated by one PI filter. In the side near
OSC, there are always one tantalum capacitor of 10uF and several ceramic
capacitors of 0.1uF or 0.01uF. As we know the resonance frequency of
tantalum capacitor is about 3MHz. If the OSC is 50MHz, the spectrum will be
speaded at 0, 50MHz, 100MHz, 150MHz, etc. There will be no power in the
frequency range between 0 and 25MHz. Therefore, I think I could remove the
tantalum capacitor. Is there something wrong?
>
>I think it will have nothing to do with the affection from OSC to outside
circuits. I am worrying about the affection from outside circuits to OSC. If
there is some noise of 2MHz and my OSC is of 50MHz, there will be modulation
between noise of 2MHz and clock signal of 50MHz. The output of OSC and the
clock signal will be affected by the noise of 2MHz. The bead will not
isolate the noise of 2MHz.
>
>I want to know I could remove the 10uF tantalum capacitor or not. Why?
>
>By the way, is there some people who do not use bead to isolate the power
supply of oscillator?
>
>Best Regards
>Zhangkun
>2002.11.12
>
>
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