OK, I've got two new PCBs here. I redesigned the comparator PCB layout from scratch - it has a couple problems:
- The input and output are single-wire, ungrounded connections. Stupid, stupid stupid stupid.
Let's see a 4ns rise square wave have to snake back through the massive loop to the one ground connection that it had......
I have no idea what I was thinking, I know better than that!
- 0603 is unnecessarily small IMO, I'm backing the size out to 0805, and I also replaced the PMSS3904/6 (SC-70) with MMBT3904/6. They're cheaper, too! I will still use the occasional SC-70 where necessary (BFS17W are much cheaper than BFS17, for instance), and TSSOP for chips with more than eight pins. Those are pretty easy.
I am considering one further small change. The 4151 diodes are a bit hard to find, and depending on the phase of the moon and what the DigiKey and Mouser stockists had for breakfast, they can be available in different footprints. I may see if I can make up a "combo" footprint that will take a SOD-80, MicroMELF, or SOD-123 (at least they're all pretty much the same shape...).
Also, the
final final AM module (no big changes, but I tidied it up a bit, it looked a bit crazy).
I'll send these out Sunday night, so hopefully we catch the mistakes that I'm sure they still have...
Nobody seems to bother looking at the 3D renders, so I'll just stop posting them and filling up Dave's server...