[SI-LIST] Re: ESD solution on antenna output
- From: "Steve Rogers" <SRogers@xxxxxxxxxxxxx>
- To: <Ibarrett@xxxxxxxxxxxxxx>, <davidjp@xxxxxxxxxxx>,<si-list@xxxxxxxxxxxxx>, <Pommerenke@xxxxxxxxxxx>
- Date: Tue, 3 Feb 2004 09:09:23 -0000
Some questions and comments...
1. Can you be more specific as to you ESD problem. Is is causing =
permenant degradation/death of a part on the radio? My guess is that =
your frying your PA transistor due to exceeding the collector-emitter =
or drain-source breakdown voltage.
2. I don't know where this suggestion of a shunt inductor to ground =
originates but this won't help and will in fact make things worse. At =
very high frequencies this will have large reactance and most of the ESD =
voltage will be developed across it. If you are going to try to get away =
with no ESD protection you want to run an output match with some series =
inductance not shunt. A match with some form of L-C filter looking from =
the antenna back to the transistor is good (hopefully this is obvious). =
A nice match is the 'T' type this gives you two inductances in the =
series path. Of course the match you can use depends on the frequency of =
operation and the power level of your transmitter (for transmitters) and =
maybe a bit dependant on the type of transistor. You could end up with =
all your possible match networks having no series inductance.
3. You dont need to worry about pushing the ESD into your ground plane. =
This is fine, you just need to make sure you dont let it generate a =
whopping voltage across the output transistor or any other susceptible =
part.=20
4. You have not mentioned the operating frequency of the radio bit? If =
its running at VHF you will have a reasonable choice of ESD suppression =
parts. Once you get up to mid UHF and more the parasitic capacitance of =
any ESD part you use must be considered. There are parts though such as =
the AVX antenna guard. These come in a number of sizes with cap down to =
as low as 3pF. If the cap needs to be lower you can run with low cap =
diodes such as those suggested in other posts.=20
5. Although the correct place to put your ESD suppressor is right on the =
antenna port, you could get away with placing it anywhere from there =
back to directly across the transistor. This gives you some freedom for =
layout and more importantly impedance matching because whatever you use =
needs to drop into your match network without pouring all your RF power =
away and causing other nasty problems.=20
6. Your radio may have antenna switching and other fancy bits after the =
final amplifier stage. If this is the case then your protection needs to =
be upstream of this.=20
7. The receiver input also needs to be afforded the same protection.=20
8. Remember to do your sums when you pick ESD bits. Before you hit your =
impedance match you can have very large voltage swings on the =
collector/drain of your output transistor. For example a typical class C =
amplifier will have collector voltage swings of twice the DC rail. If =
the design has some harmonic termination or runs class E etc then you =
can have even larger voltage swings.=20
9. Many ESD supression devices have terrible tolerance on their stray =
capacitance. You need to consider this in your design or you will end up =
with an untuned radio.
10. Finally, check out these places:
(a) Microsemi]
(b) Texas Inst
(c) California Micro devices
(d) AVX
ENJOY=20
Steve Rogers B.Eng (Hons) C.Eng IEE
RF Design Engineer
Micromill Electronics Limited
Leydene House
Waterberry Drive=20
Waterlooville Hampshire
PO7 7XX
Tel: +44 (0) 23 9236 6600
Fax: +44 (0) 23 9236 6673
Registered No. 1456922 (England). =20
Registered Office Brook Road
Wimborne, Dorset BH21 2BJ
***********************************************************************
"This email and any attached files are confidential and may be legally =
privileged.If you are not the addressee, any disclosure, =
reproduction,copying, distribution,, or other dissemination or use of =
this communication is strictly prohibited. If you have received this =
transmission in error please notify the sender immediately and then =
delete this email.
It is the policy of Micromill Electronics Limited that no legally =
binding statements, representations or commitments (collectively =
'statements') may be made by email. Any such statements must be =
confirmed either by facsimilie or by post before they will have legal =
effect. The sender of this email is not authorised to commit the company =
in any way and the addressee is hereby formally notified of that fact."
***********************************************************************
-----Original Message-----
From: Ian Barrett [mailto:Ibarrett@xxxxxxxxxxxxxx]
Sent: Monday, February 02, 2004 6:41 PM
To: 'davidjp@xxxxxxxxxxx'; si-list@xxxxxxxxxxxxx;
'Pommerenke@xxxxxxxxxxx'
Subject: [SI-LIST] ESD solution on antenna output
I am currently having a lively discussion with a colleague about an ESD
problem we have encountered. The trouble is I don't think either of us =
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 to an =
ESD
spike applied directly to it's antenna. The design includes a small =
inductor
between the antenna output and ground. My colleague (the designer) put =
it
there to try and alleviate any potential ESD problems. I have found that =
I
cannot solve the ESD susceptibility problem without removing it.
He claims 'any ESD experts will tell you to place this inductor' and =
wants
me to try and find another solution to the problem. But I think the =
inductor
is making the situation worse by coupling the ESD spike onto the ground
plane.
Can anyone offer some theory to back up either argument?
Ian.
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.org
List archives are viewable at: =20
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
=20
________________________________________________________________________
This email has been scanned for all viruses by the MessageLabs Email
Security System. For more information on a proactive email security
service working around the clock, around the globe, visit
http://www.messagelabs.com
________________________________________________________________________
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.org
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
