[SI-LIST] Re: ESD solution on antenna output (re-send)
- From: "npischl" <npischl@xxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Thu, 05 Feb 2004 03:32:54 -0000
This looks like / indicates a possible layout issue. Either the
voltage of different parts of the circuit are "pulled apart" -
voltage difference - during the ESD event, or there is induced spike
due to EM coupling/induction. Do you have split planes, connectors
between two boards or something of that nature, that would possibly
allow the abovementioned effects to happen?
Reset lines are often culprits of ESD problems, because often they
are treated as "static", and not routed as high-frequency lines.
That makes them susceptible to EMI. Also, once you understand the
problem, a SW change may help too - e.g. look for repeated
confirmation of each reset signal etc.
This is just my guess based on what you provided.
Neven
--- In si-list@xxxxxxxxxxxxxxx, Ian Barrett <Ibarrett@xxxx> wrote:
> OK update. Thanks again for all the replies, it has certainly
helped to
> clarify things in my mind.
>
> The device is a 400MHz transmitter that fits in the palm of your
hand, and
> the failure mechanism in nothing to do with the output stage -
another part
> of the circuit is going into a lock-up that requires a power cycle
to reset.
> Parallel work is looking at exactly how and why this is happening,
but I am
> looking at how the ESD is coupling into the circuit in the first
place.
>
> I have tried the experiment below - short the antenna to ground -
and the
> circuit locks-up. When I completely isolate the antenna (from the
output
> stage and any surrounding ground plane) it survives. Unfortunately,
> insulating the antenna as someone suggested, is not an option.
>
> Ian.
>
>
>
> ----- Original Message -----
> From: "Ingraham, Andrew" <a.ingraham@xxxx>
> To: <si-list@xxxx>
> Sent: Tuesday, February 03, 2004 08:57 AM
> Subject: Re: [SI-LIST] ESD solution on antenna output
>
> What would happen if you (experimentally) replace the inductor
with a short;
> i.e., directly short the antenna to ground? Of course it wouldn't
transmit
> or receive, but it might help prove/disprove your hypothesis that
the
> failure mechanism involves the ESD getting into the ground system
and then
> doing some damage there.
>
> If it is what you suspect, then we need to get into a different
mindframe.
> Most of the replies have assumed that the ESD problem is a voltage
between
> the signal and ground terminals, across the amp input or output.
But if
> it's a spike event IN the ground system, then you have to figure
out where
> it goes within your ground system and how it causes the damage.
Maybe the
> problem is that the inductor is connected to the wrong "ground"
point!
>
> An inductor to ground is used on many antenna terminals, but
apparently not
> everywhere. I think they are fairly common on HF/VHF/UHF antennas
that are
> not already self-grounding by having some sort of loop. (A base-
fed
> vertical antenna is not self-grounding, but a shunt-fed one is.)
If the
> antenna to electronics are capacitively coupled, a mobile or
outdoor
> antenna could build up several thousand volts of static charge
from wind
> and/or rain hitting it, and then you can have something like a
blown
> capacitor and electronics. Hence the inductor. It provides a DC
and low
> frequency current path to ground to bleed off this static build-
up, as Ray
> Anderson mentions.
>
> But this assumes 2-terminal (1-port) thinking; i.e., that the
enemy is
> voltage ACROSS the terminals, not something within the
electronics' ground
> system.
>
> If you think inductive kick might be worsening the problem, a few-
hundred
> ohm resistor might be better.
>
> Another variation is to use transformer coupling to the antenna,
which if
> narrowband might reject more out-of-band energy while shunting low
frequency
> ESD energy to ground.
>
> But, if you are fairly sure the problem is the ESD getting into
your ground
> plane and then causing damage, you need to think of different
solutions.
>
> Regards,
> Andy
>
>
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