[SI-LIST] Re: Analog&Digital Power planes
- From: Tayyab Jamil <tayyab@xxxxxxxxxxxxxx>
- To: sureshkumar.v@xxxxxxxxxxxxxxxxxx, si-list@xxxxxxxxxxxxx
- Date: Tue, 18 May 2004 09:54:35 +0500
Hi suresh,
For your situation the supply coming from FPGA board should be =
connected to
the digital supply of the second (a/d) board.=20
Reason is obviously the same for which we isolate digital and analog =
circuit
supplies. Digital circuit contains fast switching circuits and fast
transients on power nets are produced. Also a phenomenon called ground
bounce is common in digital circuits and we need to stop these =
transients
from going in analog word because analog circuit has no thresholds and =
even
a small noise can be amplified and generate the erronoious/noisy =
outputs.
So as per my opinion you should tie your FPGA boards supply to the =
digital
supply of 2nd baord and isolate all the analog using filter/bead.
Tayyab
-----Original Message-----
From: suresh [mailto:sureshkumar.v@xxxxxxxxxxxxxxxxxx]
Sent: Saturday, May 15, 2004 1:07 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Analog&Digital Power planes
Hello SI Experts ::
=A0
We have three PCb cards in our system.The first one is a FPGA board =
and
the second board is a analog front end card and contains a)D to A=20
converters b)A to D converters and the third board is a RF Transceiver=20
board.The "D to A" coverter gives input to the RF board and the "A to =
D"
converter gets its inputs from the RF card.
=A0
The power supply to the second board is given from the first board.Now
on=20
the second board the power planes are split into two planes a) Analog=20
supply plane and 2)Digital supply plane.Both the planes are joined at a
single point through a RF beed.
=A0
similarly the grounds are also split into two planes and joined at a
single=20
point.
=A0
QUEST::The power supply comming from the FPGA card needs to be taken as =
Digital power or the Analog power for the second card.Can somebody pls
try=20
and reason it out.
=A0
Best Regards
--=20
suresh
-
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=20
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