From: sleeper75se (sleeper75se_at_yahoo.se)
Date: 2002-03-02 17:46:40
Hi again Joerg,
I have some comments on the new PCB.
I realize that the board is not finished so forgive me if I'm
pointing out something that was about to change anyway. And some
comments are probably irrelevant.
Could you please post the latest schematic (v1.14, so the designators
match the PCB)?
Anyway, here goes:
* The two input stages (protection circuitry and instrumentation
amps) have different layouts. Since the ground planes add a fair bit
of capacitance, the HF-properties would be more similar if the
layouts matched.
* IC7 has no ground plane that prevents capacitive coupling between
the traces under it and the chip substrate. Looks like Eagle has
messed up though. Aren't the ground planes on the top and bottom the
same net?
* Linear recommends for its LT1167 that the HF-chokes (C202,C203 etc.
on the PCB) are placed as close to the input pins as possible. It's
probably safe to assume the same for INA114. On channel 2, the traces
going from R205,R206 to the inputs, are several centimeters though
they don't have to be.
* I read somewhere that you should always use 45 degree turns and
avoid 90 degree turns. Don't know if it is relevant here as this is
an LF-design.
* Design change suggestion: Why not separate analog and digital
signals into two different cables? If nothing else, it would be
nimbler, and easier to shield if necessary.
Regards,
Andreas
This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:39 BST