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?
peg...@csd4.csd.uwm.edu David R. Hucke
UW-Milwaukee Film Major
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
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.
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.
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?
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...
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
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
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.
| _ |_ _ |_| _ _| _| Electronics Department
|_| (_) | | | | | | (_| (_| (_| \/ School of MPCE
---------------------------------/- Macquarie University
Sydney, AUSTRALIA 2109
Email: jo...@mpce.mq.edu.au, Ph: +61 2 805 8959, Fax: +61 2 805 8983
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
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. *
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,
>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
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