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Alrighty, I've swapped to a SOT-89 package for the vreg, I chose an which has a bit more thermal headroom.
It also does away with the tantalum caps and uses two 1uF ceramic caps instead, so nice for a little BOM and cost reduction.

So two more questions remain.. That biasing of the prescaler and also I have yet to nail down the protection diode selection.

I was wondering about that fancy stuff going on in the inverted input of the prescaler, I thought it must have had a reason like the biasing, but datasheets don't make much mention of it...
How would one go about getting into the ballpark for the design of that network of parts before empirical testing to nail the values?
I have a handful of the prescaler chips here, so I could rig something up pretty easily.

And secondly, the diode selection.. I see that the (obsolete) diodes that HP chose have a capacitance of 26pF, but a reverse voltage rating of 4V.
How can I figure out an upper limit to the diode capacitance? higher reverse breakdown voltage means higher capacitance, so it seems to be a trade-off between durability against user abuse and performance. :D


Thanks!
Jared