[SI-LIST] Re: ESD solution on antenna output
- From: "Brent DeWitt" <bdewitt@xxxxxxxxxxxxx>
- To: <cgrassosprint1@xxxxxxxxxxxxx>, <sandord@xxxxxxxxxxxxx>,<Ibarrett@xxxxxxxxxxxxxx>
- Date: Mon, 2 Feb 2004 22:11:42 -0700
Hi Chaz,
I suspect most RF input/output semiconductors represent a excellent =
protection device for a gas discharge device! ;-}
General thoughts:
Protecting an antenna path is tough. No way around it. The series high =
Q inductor approach is terribly silly. The impulsive nature of ESD can =
ring anything below a couple of GHz, so dissipative elements are the =
only out. The frequency wasn't mentioned, but if high, could render =
many of the garden variety semiconductor devices unusable due to =
capacitive loading. Now the happy part; with the multi-billion dollar =
cell phone industry driving device manufacturers, there are low =
capacitance protection devices out there. A quick web search should =
yield a few alternatives.
Since I don't know anything about your application and ignorance is =
bliss, there are also other things to be considered:
- Is this direct discharge? Insulate the antenna.
- Is there abundant signal? Pad down the antenna to reduce the ESD =
amplitude.
- Is the RF low frequency? Roll off the input seriously.
- Is the RF narrow band? Use a dissipative band reject filter.
Best of luck!
Brent DeWitt
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Charles Grasso
Sent: Monday, February 02, 2004 10:40 PM
To: sandord@xxxxxxxxxxxxx; Ibarrett@xxxxxxxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: ESD solution on antenna output
Hi - Typically lighning protectors for antennas use some sort of =3D
sparkgap/gas discgage tube to provide protection with low capacitance. I =
=3D
agree with the folks that advocate removal of the inductor..that will =
=3D
ring under ESD conditions and make the situation a lot worse!
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Sandor Daranyi
Sent: Monday, February 02, 2004 5:10 PM
To: Ibarrett@xxxxxxxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: ESD solution on antenna output
Hello Ian,
There are ESD suppressor components offered for RF applications, but of =
=3D
cou=3D3D
rse they are highly dependent on the frequency, power, impedances etc. =
=3D
in=3D3D
volved. These parameters were not detailed in your post, so with a stab =
=3D
i=3D3D
n the dark for a small device with not very high frequency, there might =
=3D
b=3D3D
e a relevant device at=3D3D20
http://www.spkecl.com/htdoc/over-voltage-protector-ESD-Guard.htm or =3D
there a=3D3D
re other similar offerings from Littelfuse or Bussmann and others.
...but this wasn't your question. You hinted at having a solution =3D
yourself=3D3D
, which involves removing the inductor. I have to agree. It's always =
=3D
tr=3D3D
icky to make a meaningful comment without knowing the details (and I'm =
=3D
no=3D3D
t an expert), but I don't see how the inductor could provide an ESD =3D
solut=3D3D
ion in that configuration, unless the frequency of transmission is very =
=3D
h=3D3D
igh and it is guaranteed that there is not much ESD energy at =3D
frequencies=3D3D
approaching that. Ever.
The noteworthy thing is that the most likely failure mode of the =3D
inductor i=3D3D
s open, which might keep the device operating, but it can then be =3D
(perhap=3D3D
s fatally) damaged by the next serious ESD event that comes along.
What actual (physics based) explanation has your colleague offered for =
=3D
the =3D3D
inductor, apart from that all ESD experts use it? It suspiciously =3D
sounds=3D3D
like it is something that is appropriate under some specific =3D
circumstanc=3D3D
es, and has then been applied because "experts do it". People can get =
=3D
to=3D3D
uchy when they are asked about something they've done that they don't =
=3D
tot=3D3D
ally understand why... Of course, we never see that on this forum!!! =
=3D
;-=3D3D
)
Regards,
Sandor Daranyi
Senior Design Engineer
Ian Barrett wrote:
> I am currently having a lively discussion with a colleague about an =
=3D
ESD
> problem we have encountered. The trouble is I don't think either of =
=3D
us=3D3D20
> know
> enough to be able to convince the other of our point of view.
>
> The product is a small radio transmitter that is very susceptible =3D
to=3D3D20
> an ESD
> spike applied directly to it's antenna. The design includes a =
small=3D20
> inductor
> between the antenna output and ground. My colleague (the designer) put =
=3D
it
> there to try and alleviate any potential ESD problems. I have =
found=3D20
> that I
> cannot solve the ESD susceptibility problem without removing it.
>
> He claims 'any ESD experts will tell you to place this inductor' =
and=3D20
> wants
> me to try and find another solution to the problem. But I think =
the=3D20
> inductor
> is making the situation worse by coupling the ESD spike onto the =3D
ground
> plane.
>
> Can anyone offer some theory to back up either argument?
>
> Ian.
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