PCB Design

A

Assad

Guest
Hi,

I am trying to develop an Embedded board which comprises an Atmega
128L microcontroller and a CHIPCON2420 (RF section) using ORCAD. The
design requires the two sections to have seperate power and ground
planes. i.e, the Microcontroller(ATmega 128L) has its own power and
ground planes which is independent of the power and ground planes of
the CHIPCON2420(RF section). The board is supposed to have 4 layers
only. I would like to know if there is any specfic technique by which
this 4 layer PCB design is handled. I would greatly appreciate if any
of you could help me in this regard.

Regards,
Assad Ansari
 
Hi Assad,

Separating ground planes can lead to EMI and other problems. Why do they
have to be separated?

I have never had a good experience with split grounds, definitely not
when the digital side contained lots of data buses and modern (fast)
logic chips. Actually I never designed with split grounds but had to
redesign many boards into a common ground architecture after a client
was unable to pass the EMC tests or internal noise had become unmanageable.

Regards, Joerg

http://www.analogconsultants.com
 
"Assad" <sauron.nazgul@gmail.com> wrote in message
news:f81fa0cc.0411151350.2e6860ac@posting.google.com...
Hi,

I am trying to develop an Embedded board which comprises an Atmega
128L microcontroller and a CHIPCON2420 (RF section) using ORCAD. The
design requires the two sections to have seperate power and ground
planes. i.e, the Microcontroller(ATmega 128L) has its own power and
ground planes which is independent of the power and ground planes of
the CHIPCON2420(RF section). The board is supposed to have 4 layers
only. I would like to know if there is any specfic technique by which
this 4 layer PCB design is handled. I would greatly appreciate if any
of you could help me in this regard.

Regards,
Assad Ansari
Click to expand...
A plane layer need not be dedicated to a single ground or power. You can
divide it up in to multiple smaller planes.

Jeroen
 
On 12 Apr 2005 12:04:20 -0700, in sci.electronics.design
"kmaryan@gmail.com" <kmaryan@gmail.com> wrote:

So here I am, stuck trying to organize a mini-course on PCB deisgn for
those with no prior experience. I figured this group would be a good
place to start asking "what should I cover?"

Can anyone give some advice on what can go into a 3-4h session on the
basics of PCB design? The format will be primarily lecture as we don't
have the resources (or the time) to do anything hands-on.

How about some resources? Any books I should look at? Web sites? I've
already found one site that has a pretty good basic tutorial document,
but I think I want to go as far as I can in the time I have and cover
some intermediate-advanced topics.

Any thoughts?

Thanks,

Chris
slightly OT, look at the many data sheets of ADC's and DAC's and they
Click to expand...
ALL specify having seperate Digital and Analog grounds joined at one
point only.

Every time this topic is brought up here, All the SED gurus say "DONT
SPLIT THE GOUND PLANES"



martin

"Wales is a big welsh-shaped rain collection device"
 
On 12 Apr 2005 12:04:20 -0700, the renowned "kmaryan@gmail.com"
<kmaryan@gmail.com> wrote:

So here I am, stuck trying to organize a mini-course on PCB deisgn for
those with no prior experience. I figured this group would be a good
place to start asking "what should I cover?"

Can anyone give some advice on what can go into a 3-4h session on the
basics of PCB design? The format will be primarily lecture as we don't
have the resources (or the time) to do anything hands-on.

How about some resources? Any books I should look at? Web sites? I've
already found one site that has a pretty good basic tutorial document,
but I think I want to go as far as I can in the time I have and cover
some intermediate-advanced topics.

Any thoughts?

Thanks,

Chris
Click to expand...
What is the target audience?


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
 
On Tue, 12 Apr 2005 21:51:09 +0200, martin griffith
<martingriffith@XXyahoo.co.uk> wrote:

slightly OT, look at the many data sheets of ADC's and DAC's and they
ALL specify having seperate Digital and Analog grounds joined at one
point only.

Every time this topic is brought up here, All the SED gurus say "DONT
SPLIT THE GOUND PLANES"



martin

"Wales is a big welsh-shaped rain collection device"
Click to expand...


DON'T SPLIT THE GROUND PLANES!

John
 
I read in sci.electronics.design that martin griffith
<martingriffith@XXyahoo.co.uk> wrote (in
<hf9o51l25dn69cirp7d12vp190cvc5ae7p@4ax.com>) about 'PCB Design', on
Tue, 12 Apr 2005:

slightly OT, look at the many data sheets of ADC's and DAC's and they
ALL specify having seperate Digital and Analog grounds joined at one
point only.

Every time this topic is brought up here, All the SED gurus say "DONT
SPLIT THE GOUND PLANES"
Click to expand...
This does look paradoxical, but that is because both statements are
*deductions* from other, more fundamental statements:

1. Keep 'ground' as low impedance as possible. Everywhere;

2. Keep analogue currents out of digital areas of the board, and keep
digital currents out of analogue areas.

Statement 1 leads to 'Don't split the ground plane.'

Statement 2 requires you to LOOK where currents are going to flow, and
remember they flow IN LOOPS on the board. I was going to try to show in
ASCII art what that implies, but it's too difficult.

Imagine that you have the device in the centre of a square board. with
the Aground pin towards the 'west' and the Dground pin towards the east.
They are connected together, but around the device is a continuous
ground plane. Then ALL digital currents must flow substantially
westwards to the Dground, and all analogue currents must flow
substantially eastwards to the Aground.

Keep the sectors roughly from NW to NE and SW to SE for power management
and other stuff that isn't sensitive signals. If you get it right, there
should be very little analogue or digital current flowing in the strip
of ground plane perpendicular to the bridge between the Aground and
Dground pins.

But there may well be a lot of 'trash' current there, which would cause
mischief elsewhere if you split the ground plane along the length of
that strip.
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
 
Hello John,

DON'T SPLIT THE GROUND PLANES!
Click to expand...
Psssst. Don't spill the beans. After all, the more people adhere to
split grounds the more work there will be for people like us ;-)

Regards, Joerg

http://www.analogconsultants.com
 
Why is it that PCB design books cost more than the design software and your
first 3 orders from a PCB house combined? All of them are $90+

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"Stephen" <stephendeese@hotmail.com> wrote in message
news:1113333146.006208.146330@o13g2000cwo.googlegroups.com...
I've found "Printed Circuit Board Design Techniques for EMC Compliance"
and the other book by Mark Montose to be very helpful. I am a pretty
inexperienced EE who doesn't have a mentor to work with. These two
books have taught me a great deal. Don't worry about the EMC part,
they are a great references for general PCB concerns.
Click to expand...
 
On 12 Apr 2005 14:28:11 -0700, in sci.electronics.design
"kmaryan@gmail.com" <kmaryan@gmail.com> wrote:

The target audience is threefold, roughly in order of decreasing
priority:
- EEs starting out in PCB design right out of school, with no prior
knowledge
- Hobbyists advanced enough to be making PCBs, rather than just
proto-boards. (I figure with the growing availability of cheap and fast
ICs, there's some hobbyists who need to know good practices)
- people who make simple, slow circuit, noise not an issue, PCBs for a
living, but perhaps want to move to doing some digital stuff, high
speed stuff, low noise stuff...

Keep the ideas coming

Thanks,

Chris
look at the El Cheapo 5 day PCB merchants, Olimex, ExpressPCB etc, it
Click to expand...
might give you a different angle, Like "what you can get for 25 € $ Ł"
options

martin

"Wales is a big welsh-shaped rain collection device"
 
On Tue, 12 Apr 2005 20:56:36 GMT, Joerg
<notthisjoergsch@removethispacbell.net> wrote:

Hello John,

DON'T SPLIT THE GROUND PLANES!

Psssst. Don't spill the beans. After all, the more people adhere to
split grounds the more work there will be for people like us ;-)
Click to expand...






oops. sorry.

John
 
On Tue, 12 Apr 2005 18:35:08 -0400, the renowned "Glenn Ashmore"
<gashmore@cox.net> wrote:

Why is it that PCB design books cost more than the design software and your
first 3 orders from a PCB house combined? All of them are $90+
Click to expand...
Midrange price for technical books. But design software often costs
many thousands.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
 
"Glenn Ashmore" <gashmore@cox.net> wrote in message
news:t2Y6e.1874$Z73.791@lakeread04...
Why is it that PCB design books cost more than the design software and
your first 3 orders from a PCB house combined?
Click to expand...
Because you're using cheap software and cheap board houses? Much PCB design
software still has a 4 digit price tag, and I imagine that there's some
that's still 5. Similarly, go get some price quotes for 8 or 12 layer
boards and then start complaining about book prices...

Seriously, if you can't afford books, there is plenty of free PCB layout
information available on the Internet. Nevertheless, there are books that
are easily worth more than the asking price in that they can save you a lot
more time than that many hour's wages would pay...
 
Hello Chris,

They're basically text books, in that realm $100/book isn't unusual.
Most eng students budget $500/term or more for books. Perhaps we are
being gouged, but it's not like these are bestsellers, so it might just
be a supply/demand thing.
Click to expand...
That's the point. They might sell a few thousand total, if that. So it
can't be produced at the same cost as an Agatha Christie thriller in
paperback.

Regards, Joerg

http://www.analogconsultants.com
 
Hello Chris,

I'd do a hands-on seminar instead, no dry teaching from the pulpit. Get
a cheap but good CAD program such as Eagle. That has schematic and
layout nicely integrated and there are freeware and educational versions.

Then show the audience the actual work, explaining what you do and why.
Of course, the auditorium needs to be equipped with a good projector
(and a spare bulb...) and ideally with WLAN so the students can also
follow on their own laptops.

Regards, Joerg

http://www.analogconsultants.com
 
kmaryan@gmail.com wrote:

So here I am, stuck trying to organize a mini-course on PCB deisgn for
those with no prior experience. I figured this group would be a good
place to start asking "what should I cover?"

Can anyone give some advice on what can go into a 3-4h session on the
basics of PCB design? The format will be primarily lecture as we don't
have the resources (or the time) to do anything hands-on.
Click to expand...
So here I am, stuck trying to organize a mini-course on eye
surgery for those with no prior experience.

Can anyone give some advice on what can go into a 3-4h session
on the basics of operating on the human eye? The format will be
primarily lecture as we don't have the resources (or the time) to
do anything with actual eyeballs.

(In other words, either take the time to educate them properly, or
don't educate them at all and hire someone who is already educated.
The world already has quite enough marginals layouts already
without you making people think they can do a layout after a four
hour lecture.)

BTW, don't split ground planes. :)
 
On Wed, 13 Apr 2005 12:06:06 +0000, in sci.electronics.design Guy
Macon <http://www.guymacon.com/> wrote:

kmaryan@gmail.com wrote:

So here I am, stuck trying to organize a mini-course on PCB deisgn for
those with no prior experience. I figured this group would be a good
place to start asking "what should I cover?"

Can anyone give some advice on what can go into a 3-4h session on the
basics of PCB design? The format will be primarily lecture as we don't
have the resources (or the time) to do anything hands-on.

So here I am, stuck trying to organize a mini-course on eye
surgery for those with no prior experience.

Can anyone give some advice on what can go into a 3-4h session
on the basics of operating on the human eye? The format will be
primarily lecture as we don't have the resources (or the time) to
do anything with actual eyeballs.

(In other words, either take the time to educate them properly, or
don't educate them at all and hire someone who is already educated.
The world already has quite enough marginals layouts already
without you making people think they can do a layout after a four
hour lecture.)

BTW, don't split ground planes. :)





http://uk.geocities.com/martingriffith/dilbertteachme.gif
Click to expand...


martin

"Wales is a big welsh-shaped rain collection device"
 
I read in sci.electronics.design that Guy Macon
<http@?.guymacon.com/.invalid> wrote (in
<115q2q33hcav82c@corp.supernews.com>) about 'PCB Design', on Wed, 13 Apr
2005:

BTW, don't split ground planes. :)
Click to expand...

But any planes with splits must be grounded immediately.
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
 
I read in sci.electronics.design that "kmaryan@gmail.com"
<kmaryan@gmail.com> wrote (in
<1113409635.565356.170590@f14g2000cwb.googlegroups.com>) about 'PCB
Design', on Wed, 13 Apr 2005:
I'm not claiming to make anyone an experienced designer here. This is
going to be a small, free, seminar offered by a non-profit group to
local EEs. The first thing out of my mouth is probably something along
the lines of "This does not qualify you to design anything, for that
you need experience, but it does cover the basic issues so you can keep
them in mind."

So if you were going to "educate them properly" what topics would you
go over? Hands on may be difficult given our resources, but I can still
include plenty of worked examples of good vs bad practices and why
things are done one way or the other.

Yes, you have to start somewhere. In my case, it was a guest lecture at
Click to expand...
college by the putative inventor of the etched PCB, an Austrian IIRC.
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
 
On Wed, 13 Apr 2005 09:27:15 -0700, kmaryan@gmail.com wrote:

I'm not claiming to make anyone an experienced designer here. This is
going to be a small, free, seminar offered by a non-profit group to local
EEs. The first thing out of my mouth is probably something along the lines
of "This does not qualify you to design anything, for that you need
experience, but it does cover the basic issues so you can keep them in
mind."

So if you were going to "educate them properly" what topics would you go
over? Hands on may be difficult given our resources, but I can still
include plenty of worked examples of good vs bad practices and why things
are done one way or the other.
Click to expand...
Get pre-sensitized board stock, watch your exposure time and light
source (I used sunlight the time I did one) and watch your etch times and
etchant concentration, and agitate.

You can drill before or after etching, and you can simulate plated-
through holes with a piece of #30 wire. If you absolutely need real
plated-through holes, send it out.

If you do double-sided, be sure to give yourself register marks OFF the
main board real estate. I laid a little board out decades ago, by hand
with tape and peel-off stickers and an X-acto knife and all that crap,
at 2X, and had the print shop print it 6-up while maintaining
registration,for a surprisingly reasonable amount of money.

For huge ground/power planes, consider using some kind of lattice, and
don't forget the thermal relief!

Good Luck!
Rich
 
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