From: sleeper75se (sleeper75se_at_yahoo.se)
Date: 2002-01-15 05:55:06
Hi all,
I've uploaded a composite of the layout for the input stage to the
files section. The board size is 160x100 mm, so there is plenty of
room left.
An SMT-version would of course be *much* smaller ...
The PCB is double sided, with a ground plane on top (not shown) and
all traces at the bottom, although it looks like they are on top in
the picture.
Some points worthy of notice, and perhaps criticism? :
* The inputs are guarded by a special plane connected to the shield
drivers. If you do not believe in shield drivers, it is an easy task
to connect the plane to ground instead.
* The empty space in the middle of the board is reserved for a DRL.
* The negative power rail passes under U102 and U202. It goes to the
center pin on the right side of the IC. I hope I've successfully
avoided routing it directly under the chip. One option is to route it
around the column of capacitors, but that could create a big current
loop instead.
* The decoupling capacitors are not as close to the IC's as possible.
Again, this is because placing them close would mean the signal path
would move around the board in bigger loops. To compensate, I've made
the trace between the 100nF capacitor and IC really fat - 40 mils. I
hope this is enough.
* All those little vias on the ground plane connects the bottom with
the top layer. There should be more of them...
* I have not made a proper analysis of how the currents flow. I've
just followed my intuition. But that is not to be trusted. :-)
* The in-amp reference input on pin 5 is fed by the integrator. This
means the signal must travel several inches from U102/U202 pin 1 to
the instrumentation amp. However, it moves parallel to the output
from the in-amp (pin 6, U100/U200) as much as possible.
* I need to sleep. I've been awake 24 hrs now, so if you see
something strange in the layout, it's probably because of that.
* It is not a pretty layout, but the day I'll be able to do pretty
layouts is the day after hell freezes over. :-P
Please tell me what you think needs changing and then I can fix that
and upload the layout in a usable form.
/Andreas
This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:36 BST