Lpc2000

Hi. Sorry for the offtopic, guys. If anybody can point me out some good 
forum/group to post this question, I'll be glad.

I need to calculate trace witdh and cleareance to achive an impedance 
of nearly 50 ohm for an RF trace surrounded by a GND polygon. My board 
is SINGLE layered, so I have no power or GND planes. There's plenty of 
online calculators for this *if* I have a GND plane, but I couldn't 
find any for surface impedance calculation (i.e., between tracks). Any 
hints?

Guille

--- In lpc2000@yahoogroups.com, "Guillermo Prandi" 
<yahoo.messenger@...> wrote:
>
> Hi. Sorry for the offtopic, guys. If anybody can point me out some 
good 
> forum/group to post this question, I'll be glad.
> 
> I need to calculate trace witdh and cleareance to achive an impedance 
> of nearly 50 ohm for an RF trace surrounded by a GND polygon. My 
board 
> is SINGLE layered, so I have no power or GND planes. There's plenty 
of 
> online calculators for this *if* I have a GND plane, but I couldn't 
> find any for surface impedance calculation (i.e., between tracks). 
Any 
> hints?
> 
> Guille
>

Oh, never mind. The price difference between single and double layer is 
minimal.

Thanks anyway.

Guille

----- Original Message ----- 

From: "Guillermo Prandi" <yahoo.messenger@...>
To: <lpc2000@yahoogroups.com>
Sent: Wednesday, May 03, 2006 12:50 PM
Subject: [lpc2000] OFFTOPIC: PCB impedance calculation without GND plane


> Hi. Sorry for the offtopic, guys. If anybody can point me out some good
> forum/group to post this question, I'll be glad.
>
> I need to calculate trace witdh and cleareance to achive an impedance
> of nearly 50 ohm for an RF trace surrounded by a GND polygon. My board
> is SINGLE layered, so I have no power or GND planes. There's plenty of
> online calculators for this *if* I have a GND plane, but I couldn't
> find any for surface impedance calculation (i.e., between tracks). Any
> hints?

You will find it impossible to get a 50 ohm impedance the way you describe. 
Why not just put some copper pour on the other side of the track, making it 
a microstrip section. A track width of 0.1" will give you about 50 ohms with 
FR4 material. If you are stuck with a single-sided board you could glue a 
piece of copper foil to the other side of the board or use some 50 ohm coax 
cable. If the connection is short and the frequency not all that high, I 
wouldn't bother with impedance matching anyway.

Leon
--
Leon Heller, G1HSM
leon.heller@...
http://www.geocities.com/leon_heller

Leon 

---
[This E-mail has been scanned for viruses but it is your responsibility 
to maintain up to date anti virus software on the device that you are
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--- In lpc2000@yahoogroups.com, "Leon Heller" <leon.heller@...> wrote:
>
> ----- Original Message ----- 
> From: "Guillermo Prandi" <yahoo.messenger@...>
> To: <lpc2000@yahoogroups.com>
> Sent: Wednesday, May 03, 2006 12:50 PM
> Subject: [lpc2000] OFFTOPIC: PCB impedance calculation without GND 
plane
> 
> 
> > Hi. Sorry for the offtopic, guys. If anybody can point me out 
some good
> > forum/group to post this question, I'll be glad.
> >
> > I need to calculate trace witdh and cleareance to achive an 
impedance
> > of nearly 50 ohm for an RF trace surrounded by a GND polygon. My 
board
> > is SINGLE layered, so I have no power or GND planes. There's 
plenty of
> > online calculators for this *if* I have a GND plane, but I 
couldn't
> > find any for surface impedance calculation (i.e., between 
tracks). Any
> > hints?
> 
> You will find it impossible to get a 50 ohm impedance the way you 
describe. 
> Why not just put some copper pour on the other side of the track, 
making it 
> a microstrip section. A track width of 0.1" will give you about 50 
ohms with 
> FR4 material. If you are stuck with a single-sided board you could 
glue a 
> piece of copper foil to the other side of the board or use some 50 
ohm coax 
> cable. If the connection is short and the frequency not all that 
high, I 
> wouldn't bother with impedance matching anyway.
> 
> Leon
> --
> Leon Heller, G1HSM
> leon.heller@...
> http://www.geocities.com/leon_heller
> 
> Leon 
> 
> ---
> [This E-mail has been scanned for viruses but it is your 
responsibility 
> to maintain up to date anti virus software on the device that you 
are
> currently using to read this email. ]
>

Thanks, Leon. I'll keep in mind your suggestions if I bump into this 
problem again, but you're right, a second layer is way easier. The 
line is relatively short (1 inch), but frequency is GSM (1.8/1.9 
GHz), so I want to be careful to keep signal integrity in good shape 
as much as I can within reason.

Guille

----- Original Message ----- 

From: "Guillermo Prandi" <yahoo.messenger@...>
To: <lpc2000@yahoogroups.com>
Sent: Wednesday, May 03, 2006 2:34 PM
Subject: [lpc2000] Re: OFFTOPIC: PCB impedance calculation without GND plane


> --- In lpc2000@yahoogroups.com, "Leon Heller" <leon.heller@...> wrote:
>>
>> ----- Original Message ----- 
>> From: "Guillermo Prandi" <yahoo.messenger@...>
>> To: <lpc2000@yahoogroups.com>
>> Sent: Wednesday, May 03, 2006 12:50 PM
>> Subject: [lpc2000] OFFTOPIC: PCB impedance calculation without GND
> plane
>>
>>
>> > Hi. Sorry for the offtopic, guys. If anybody can point me out
> some good
>> > forum/group to post this question, I'll be glad.
>> >
>> > I need to calculate trace witdh and cleareance to achive an
> impedance
>> > of nearly 50 ohm for an RF trace surrounded by a GND polygon. My
> board
>> > is SINGLE layered, so I have no power or GND planes. There's
> plenty of
>> > online calculators for this *if* I have a GND plane, but I
> couldn't
>> > find any for surface impedance calculation (i.e., between
> tracks). Any
>> > hints?
>>
>> You will find it impossible to get a 50 ohm impedance the way you
> describe.
>> Why not just put some copper pour on the other side of the track,
> making it
>> a microstrip section. A track width of 0.1" will give you about 50
> ohms with
>> FR4 material. If you are stuck with a single-sided board you could
> glue a
>> piece of copper foil to the other side of the board or use some 50
> ohm coax
>> cable. If the connection is short and the frequency not all that
> high, I
>> wouldn't bother with impedance matching anyway.
>>
>> Leon
>> --
>> Leon Heller, G1HSM
>> leon.heller@...
>> http://www.geocities.com/leon_heller
>>
>> Leon
>>
>> ---
>> [This E-mail has been scanned for viruses but it is your
> responsibility
>> to maintain up to date anti virus software on the device that you
> are
>> currently using to read this email. ]
>>
>
> Thanks, Leon. I'll keep in mind your suggestions if I bump into this
> problem again, but you're right, a second layer is way easier. The
> line is relatively short (1 inch), but frequency is GSM (1.8/1.9
> GHz), so I want to be careful to keep signal integrity in good shape
> as much as I can within reason.

Yes, for GSM you do need to take some care with the track. I'm using a 
Siemens MC55 module which has a tiny Hirose coax socket (about 2.5 mm wide) 
for the antenna as well as an optional pad for connection to a PCB. I'm 
using the former as it makes things easier, although I had to buy an SMA 
adapter cable. I'm actually using a home-made single-sided PCB with it.

Guillermo Prandi wrote:

>--- In lpc2000@yahoogroups.com, "Guillermo Prandi" 
><yahoo.messenger@...> wrote:
>  
>
>>Hi. Sorry for the offtopic, guys. If anybody can point me out some 
>>    
>>
>good 
>  
>
>>forum/group to post this question, I'll be glad.
>>
>>I need to calculate trace witdh and cleareance to achive an impedance 
>>of nearly 50 ohm for an RF trace surrounded by a GND polygon. My 
>>    
>>
>board 
>  
>
>>is SINGLE layered, so I have no power or GND planes. There's plenty 
>>    
>>
Since RF is RF and not digital or analog, you may want to ask around 
some of the lists which deal with RF.  For example, Ham Radio (Amateur 
Radio).  I have an old copy of the: G.R. Jessop,G6JP "VHF UHF Manual", 
ISBN #0-900612-92-4

Jessop goes into a lot of detail about microwave and one section of the 
book deals with microstripline transmission circuits.  Both using double 
clad PCB as well as transmission line charactoristics of various types 
of materials: slab lines (PCB traces), parallel wires, wire parallel to 
infinite plane, wire in rectangular trough, etc.

For slablines:

=============== begin formula ======================


Where B is the overall length of the two parallel slabs, and, A == 
inside distance between the slabs:

Zo ~= 377 * (A / B)

(IOW Zout is approximately equal to 377 times A / B).

And, given that A << B then "edge effects are neglected"


================== snip =====================


That example is for two slablines in freespace.  However, depending on 
the cross-sectional area of the slabs, I would suspect that the effect 
of the PCB surface would be negligable.

If you present the line with a known impedance, design the slab line for 
that impedance and terminate in the same impredance, then you do not 
have to worry about 1/4 wavelength effects.  Radically change any of the 
three impedances and the wavelength of the line becomes a factor.

My copy is rather dated, 1991, but it is an excellent reference.

Regards,

TomW

-- 
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net, http://cyberiansoftware.com
"Windows? No thanks, I have work to do..."
----------------------------------------------------

Hi Guillermo. Have you tried AppCAD? It's a free download from the Agilent website.

Guillermo Prandi <yahoo.messenger@...> wrote:  Hi. Sorry for the offtopic, guys. If anybody can point me out some good 
forum/group to post this question, I'll be glad.

I need to calculate trace witdh and cleareance to achive an impedance 
of nearly 50 ohm for an RF trace surrounded by a GND polygon. My board 
is SINGLE layered, so I have no power or GND planes. There's plenty of 
online calculators for this *if* I have a GND plane, but I couldn't 
find any for surface impedance calculation (i.e., between tracks). Any 
hints?

Guille





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[Non-text portions of this message have been removed]

Thanks, Tom!

--- In lpc2000@yahoogroups.com, Tom Walsh <tom@...> wrote:
>
> Guillermo Prandi wrote:
> 
> >--- In lpc2000@yahoogroups.com, "Guillermo Prandi" 
> ><yahoo.messenger@> wrote:
> >  
> >
> >>Hi. Sorry for the offtopic, guys. If anybody can point me out 
some 
> >>    
> >>
> >good 
> >  
> >
> >>forum/group to post this question, I'll be glad.
> >>
> >>I need to calculate trace witdh and cleareance to achive an 
impedance 
> >>of nearly 50 ohm for an RF trace surrounded by a GND polygon. My 
> >>    
> >>
> >board 
> >  
> >
> >>is SINGLE layered, so I have no power or GND planes. There's 
plenty 
> >>    
> >>
> Since RF is RF and not digital or analog, you may want to ask 
around 
> some of the lists which deal with RF.  For example, Ham Radio 
(Amateur 
> Radio).  I have an old copy of the: G.R. Jessop,G6JP "VHF UHF 
Manual", 
> ISBN #0-900612-92-4
> 
> Jessop goes into a lot of detail about microwave and one section of 
the 
> book deals with microstripline transmission circuits.  Both using 
double 
> clad PCB as well as transmission line charactoristics of various 
types 
> of materials: slab lines (PCB traces), parallel wires, wire 
parallel to 
> infinite plane, wire in rectangular trough, etc.
> 
> For slablines:
> 
> =============== begin formula ======================
> 
> 
> Where B is the overall length of the two parallel slabs, and, A == 
> inside distance between the slabs:
> 
> Zo ~= 377 * (A / B)
> 
> (IOW Zout is approximately equal to 377 times A / B).
> 
> And, given that A << B then "edge effects are neglected"
> 
> 
> ================== snip =====================
> 
> 
> That example is for two slablines in freespace.  However, depending 
on 
> the cross-sectional area of the slabs, I would suspect that the 
effect 
> of the PCB surface would be negligable.
> 
> If you present the line with a known impedance, design the slab 
line for 
> that impedance and terminate in the same impredance, then you do 
not 
> have to worry about 1/4 wavelength effects.  Radically change any 
of the 

> three impedances and the wavelength of the line becomes a factor.
> 
> My copy is rather dated, 1991, but it is an excellent reference.
> 
> Regards,
> 
> TomW
> 
> -- 
> Tom Walsh - WN3L - Embedded Systems Consultant
> http://openhardware.net, http://cyberiansoftware.com
> "Windows? No thanks, I have work to do..."
> ----------------------------------------------------
>

Thanks, Bisser. I didn't know this program. Now I added it to 
my 'useful tools' folder!

Guille

--- In lpc2000@yahoogroups.com, Bisser Gatchev <begatchev@...> wrote:
>
> Hi Guillermo. Have you tried AppCAD? It's a free download from the 
Agilent website.
> 
> Guillermo Prandi <yahoo.messenger@...> wrote:  Hi. Sorry for the 
offtopic, guys. If anybody can point me out some good 
> forum/group to post this question, I'll be glad.
> 
> I need to calculate trace witdh and cleareance to achive an 
impedance 
> of nearly 50 ohm for an RF trace surrounded by a GND polygon. My 
board 
> is SINGLE layered, so I have no power or GND planes. There's plenty 
of 
> online calculators for this *if* I have a GND plane, but I couldn't 
> find any for surface impedance calculation (i.e., between tracks). 
Any 
> hints?
> 
> Guille
> 
> 
> 
> 
> 
>   SPONSORED LINKS 
>         Microcontrollers   Microprocessor   Intel microprocessors 
>     
> ---------------------------------
>   YAHOO! GROUPS LINKS 
> 
>     
>     Visit your group "lpc2000" on the web.
>     
>     To unsubscribe from this group, send an email to:
>  lpc2000-unsubscribe@yahoogroups.com
>     
>     Your use of Yahoo! Groups is subject to the Yahoo! Terms of 
Service. 
> 
>     
> ---------------------------------
>   
> 
> 
> 
> 		
> ---------------------------------
> New Yahoo! Messenger with Voice. Call regular phones from your PC 
and save big.

> 
> [Non-text portions of this message have been removed]
>

--- In lpc2000@yahoogroups.com, "Guillermo Prandi"
<yahoo.messenger@...> wrote:
>
> Thanks, Tom!
> 

A general rule of thumb with RF circuits is that traces which are less
than 1/10th of the wavelength of the highest frequency involved have a
negligible effect. 

I wouldn't like to run an unshielded RF signal next to any sort of
high speed digital device though.

Mike

Mike wrote:

>--- In lpc2000@yahoogroups.com, "Guillermo Prandi"
><yahoo.messenger@...> wrote:
>  
>
>>Thanks, Tom!
>>
>>    
>>
>
>A general rule of thumb with RF circuits is that traces which are less
>than 1/10th of the wavelength of the highest frequency involved have a
>negligible effect. 
>
>  
>
Good point, thanks!

TomW

-- 
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net, http://cyberiansoftware.com
"Windows? No thanks, I have work to do..."
----------------------------------------------------