Re: [SI-LIST] : Alternate ESD Techniques

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From: Douglas C. Smith (doug@dsmith.org)
Date: Mon Aug 14 2000 - 17:56:36 PDT


Hi Peter,

I am thinking more of a connected cable and a network that
would sit between the cable and EUT. The network provides
lots of common mode rejection, elimination of unneeded
bandwidth, and (in the case of UTP (unshielded cable) use of
the extra pairs and their mutual inductance to the used
pairs to provide an extra factor of two or more "shielding
effectiveness" when properly connected.

One such network I designed back in my Bell Labs days, gave
UTP CAT 5 cable better ESD immunity than good quality
coaxial cable had in a computer networking application. A
patent was obtained by Bell Labs on that circuit.

If the pin is exposed, signal corruption is not an issue
since there is no signal transmitted. However, international
standards appear to be moving away from having to test
individual exposed pins of a connector. The question may
become moot, except in unusual cases if this happens.

Doug

Peter Baxter wrote:
>
> Hi Doug,
>
> You mention "by other design techniques", in the following paragraph.
>
> Devices such as these can prevent damage if properly used. However, data
> corruption on the protected lines is still likely to occur and must be
> handled by other design
> techniques. In quite a few cases, these techniques can eliminate the
> need for the protective devices in the first place.
>
> Douglas C. Smith
>
> If you had an exposed pin, connected to an IC, that can be touched by
> human contact (an oscilliscope probe is an example, but a poor example -
> as it has attenuation networks in it), (PC Printer socket is a better
> example - as it is high speed and possibly a direct connection (via a
> current limit resistor?))
>
> What alternative techniques might you suggest be considered?
>
> Regards,
>
> Peter Baxter
>
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