What is a PCB with a Ground plane?

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David R Hucke

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Aug 7, 1992, 7:02:19 PM8/7/92
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Thanks to all who helped me with my wire wrapping question...

What exactly is a ground plane? Can I make one myself and stick it
on a prototype board? Or do I need to buy a board specifically with
a ground plane?


Thanks again..


--
peg...@csd4.csd.uwm.edu David R. Hucke
UW-Milwaukee Film Major
--

Larrie Simon Carr

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Aug 7, 1992, 8:05:34 PM8/7/92
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In article <1992Aug7.2...@uwm.edu> peg...@csd4.csd.uwm.edu (David R Hucke) writes:
>Thanks to all who helped me with my wire wrapping question...
>
>What exactly is a ground plane? Can I make one myself and stick it
>on a prototype board? Or do I need to buy a board specifically with
>a ground plane?
>
>
>Thanks again..

Physically, it basically one layer on a multilayer PCB that is dedicated
as a ground. A good ground plane covers the entire layer except for
via's and thru hole areas.

Benefits include decreased inductance on circuit ground and less cross-talk
between traces.

If you have a single sided board, you can use the other side as a ground
plane. Otherwise you will have to go >2 layers which is too expensive
for most people.

A ground plane becomes important for frequencies >10 - 20 MHz. Depends
on the application, chip technology used and design.


--
Larrie Carr
Engineering Science (604) 291-4451
Simon Fraser University (604) 298-1050
British Columbia, Canada lar...@sfu.ca

Glenn A Sullivan

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Aug 7, 1992, 9:26:58 PM8/7/92
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The latest issue of RF DESIGN has its first really useful article on
the underpinnins of oscillator phase noise.
This is Audust 1992, page 50--57, by Constantine Fantanas.

I've also read the relevant chapters in Van der Zaal (spelling?).

The LO for CH2/3/5 in the tuner I recently designed, at 101/107/113 MHz,
has far-out sideband energy AT LEAST 70dB down, limited by the spectrum
analyzer. This is for greater than 100KHz offset.
OFFSET dBc
100 Hz -30
500 Hz -50
1000 Hz -60
100,000 Hz -70+

We get excellent demodulated video! Yet I see a faint flicker in the chroma,
and wonder if untracked LO phase noise might slightly upset the synchronous
demodulator (MC44301, Motorola), since the AFT loop is quite slow (10Hz)
and the demodulator PLL is about 5KHz bandwidth?
Are these values bad? Colpitts oscillator, using NE602, on ground plane,
MV2101 (Motorola) varactor, running 1 to 4 volts. No cavity (100MHz),
just generic 8pF NPO chip caps, not American Technical Ceramics; inductor
of 100nanoH has Q about 30. LO size is 1cm X 2.5cm.

To get extra LO power, and thus about 4dB more Mixer gain, I boosted the
(internal) oscillator emitter current by about 4X

Anyway, any ideas on improvements? Silver-plated inductor? ATC caps?
Lower the LO emitter current, to alter its noise figure? Add 3X3cm shielding,
to check for external RFI pickup?

Allen Sullivan
gsul...@enuxha.eas.asu.edu


David J W Emrich

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Aug 9, 1992, 9:45:16 AM8/9/92
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peg...@csd4.csd.uwm.edu (David R Hucke) writes:


>Thanks again..

The ground plane is as the name suggests, a layer of copper connected to
ground. It's main use is suppressing crosstalk across tracks on the
PCB. Generally it is the middle layer of copper in a three layer board,
and it is the reverse of the pad layout. I.e. it is a continuous sheet
of copper, etched to remove pad-sized holes wherever a component lead or
lead through (link from top layer to bottom) pass through. Commercial
PCBS are made this way by etching two or more separate "thin" fiberglass
boards, and heat-and-resin-bonding them together.

The only practical way for a do-it-yourselfer-ground plane is if you are
using only a single conductor layer on your board (i.e. if it wasn't for
the ground plane, you would have a double layer board). Various
experimental boards have been made from two separated PCBS, but the
disadvantages are obvious, Thick boards, and the difficulty of lining up
the two boards (requires EXACT drilling!!).

Hope this is useful...

[dav] aka
David Emrich
gu...@uniwa.uwa.edu.au

srg...@grace.dsir.govt.nz

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Aug 9, 1992, 5:35:04 PM8/9/92
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Haven't been following this, but if you want to add ground planes to PCBs
I wrote a utility to do this. It requires the artwork to be in the form of
a laserjet printer file ( we use a program called EAGLE from Cadsoft).
The program is called XFILL10.ZIP in MSDOS.ELECTRONICS on Simtel-20
--
Bruce Spedding
Materials Science and Performance
Industrial Research Ltd, Fax: +64-4-569-0132
P.O.Box 31310, Work: +64-4-569-0485
Lower Hutt, ( NZST : +12 ) Home: +64-4-562-8522
New Zealand. Internet: srg...@grv.grace.cri.nz

John Haddy

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Aug 9, 1992, 6:55:47 PM8/9/92
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In article <1992Aug8.0...@sfu.ca>, lar...@beaufort.sfu.ca (Larrie Simon Carr) writes:
|> In article <1992Aug7.2...@uwm.edu> peg...@csd4.csd.uwm.edu (David R Hucke) writes:
|> >Thanks to all who helped me with my wire wrapping question...
|> >
|> >What exactly is a ground plane? Can I make one myself and stick it
|> >on a prototype board? Or do I need to buy a board specifically with
|> >a ground plane?
|> >
|> >
|> >Thanks again..
|>
|> Physically, it basically one layer on a multilayer PCB that is dedicated
|> as a ground. A good ground plane covers the entire layer except for
|> via's and thru hole areas.
|>
|> If you have a single sided board, you can use the other side as a ground
|> plane. Otherwise you will have to go >2 layers which is too expensive
|> for most people.
|>
If you're wire wrapping, you can use a single sided copper-clad board if you're
prepared to do the drilling for your W/W sockets yourself and if you have access
to something like a small engraver. Drill the power and ground holes for each IC
just big enough for a clearance fit. Drill all other holes about 1mm bigger (so
that the signal pins do not contact the copper plane. Use the engraver to create
an isolated donut shape for the power pins. Solder your W/W sockets to the power
islands and ground plane copper.

Alternatively, I have seen (_long_ ago) commercial W/W prototyping boards with a
ground plane on the upper side. These required that a link be made from your IC
ground pin back up to the upper side of the board.

You might get away with making something like this yourself, using copper foil
adhesive tape across all unused space on the top of your board. Just remember to
solder jumpers between each strip of tape used.

This may be too much bother - around here its faster (and cheaper) to jump
straight to a PCB prototype than to spend much time in getting a W/W board ready
and then wired. We haven't, in fact, made a W/W board in over four years.

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Mike Fox

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Aug 10, 1992, 2:23:35 PM8/10/92
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The previous postings have answered the question, here are
a few more points. If you have a high frequency PWB or don't
have much real-estate - this is a must. Also, you will probably
want a power plane as well. It is best to place power or ground
planes between signal planes. If you have to put two signal
planes next to each other look out for clocks over data bus'
and try not to place two planes with etches predominately in
the same direction next together.

As to the higher costs, the person doing the artwork will
certainly appreciate your separating gound and power planes
as it makes their life MUCH easier. A multi-layer board doesn't
add that much more drilling than a single or 2 layer board.
Therefore, the extra cost will be primarily driven by the board
fab shop. I would get some quotes on 2sided vs multi-layer
boards.

Jim Ray

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Aug 10, 1992, 2:11:03 PM8/10/92
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Ground and power planes are really cool for PCB's, but my home project
must use wirewrap instead of $$$ multi-layer PCB. Any other ideas?

*****************************************************************
* *
* Jim Ray r...@eecs.nwu.edu *
* *
* The opinions expressed are my own and not my mama's. *
* *
*****************************************************************

Tony Duell

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Aug 11, 1992, 7:12:29 AM8/11/92
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For ground plane on w/w circuits. Try either of the following.
1) Over here in England (and I guess in hte states also), you cna buy
protoboards with a ground plane. They work _very_ well, I have built 30-40
MHz stuff on them with no problems. A bit expensive though - about $80 for
a double eurocard.
2) get a piece of copper-clad the size you need, and drill holes where you
want to pu things. Then either enlarge the hole on the copper side only of
things you don't want grounded (say about 3mm), or use a PCB counterbore
if you can get one. That tool will cut a small pad round each hole. Now
insert and solder your parts, and w/w the circuit. The copper-clad baord
will make a ground plane.
-tony 'PDP11 Hacker' Duell
a...@siva.bris.ac.uk

Andy Warner

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Aug 11, 1992, 10:57:18 AM8/11/92
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In article <1992Aug10.1...@eecs.nwu.edu>, r...@eecs.nwu.edu (Jim Ray) writes:
> [...]

> Ground and power planes are really cool for PCB's, but my home project
> must use wirewrap instead of $$$ multi-layer PCB. Any other ideas?

Some people answered the question "what's a ground plane" without
knowing the context in which it arose.. sorry 'bout that..

At places like Halted Specialities & Frys in CA, I've seen decent
sized W/W boards with ground planes. Digi-Key sells a smaller
version (that I use a lot of) [page 202, part # V1049-ND, in their
July-August 1992 catalogue].

They are a little more expensive, but if you value your sanity,
they are worth it.

On an allied thread, I too wire-wrap using a manual tool (which
raises quite a few eyebrows, "you did all _this_ by hand ?") I
find it slows me down enough to stop me making too many stupid
mistakes. It does make a strange mark in the pam of your hand,
though..
--
andyw. N0REN/G1XRL

an...@aspen.cray.com Andy Warner, Cray Research, Inc. (612) 683-5835

John Whitmore

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Aug 11, 1992, 8:02:07 PM8/11/92
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In article <1992Aug7.2...@uwm.edu> peg...@csd4.csd.uwm.edu (David R Hucke) writes:

>What exactly is a ground plane? Can I make one myself and stick it
>on a prototype board? Or do I need to buy a board specifically with
>a ground plane?

Basic physics: current in a wire causes a magnetic field.
Changing magnetic field causes a voltage in a wire. Two wires, therefore,
form a transformer: put a changing current in one wire, get
a signal voltage out of the other.

Slightly more advanced physics: the addition of a grounded plane
in the problem creates an IMAGE CURRENT. The changing current in
wire #1 is accompanied by an equal and opposite image current in
the ground plane, effectively due to a wire which is the mirror
image of the first wire (and the mirror plane is the ground plane).
The induced voltage (EMF) on wire #2 is then the sum of the EMF
due to the current in #1, and the opposite EMF due to the image
current. The EMF's cancel each other out.

The higher the frequency, the more abruptly the current
in wire #1 changes, and the greater the EMF becomes. A ground
plane 1/4" from the wiring may be effective at low frequencies,
and with insensitive signal paths. A ground plane inside a
multilayer circuit board may be required at higher frequencies
(the closer that image current is to the driving current, the
more nearly the EMF it induces will cancel the EMF due to the
driving current).

At the highest frequencies, ground planes are a very good
protection against unwanted signal coupling that one can build into
a PC board. Other techniques include twisted-pair wiring, coaxial
cables (the image current is an EXACT cancellation for coaxial
wiring) and so-called 'stripline' wiring (which uses both a
ground plane and some wiring dimension control). Ground
planes are also important in low-frequency circuits, because
any high-frequency COMPONENTS can accidentally couple (and
oscillate).

John Whitmore

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