I'm laying out a TO package using the AD8015, and I have a few questions about some recommendations in the data sheet:
1. On pg. 3, under the metallization photograph, there's a note that says "for best performance attach package substrate to +Vs", but that either +Vs or -Vs is acceptable. What's the consideration here?
2. Again on pg. 3, it's mentioned that the bypass cap C1 can be connected to signal ground, or to +Vs for improved noise immunity in the case where power supply noise is large. If power supply noise isn't large, is it preferable to connect C1 to signal ground?
3. In fig. 4, the photodiode bias is bypassed to +Vs, but in fig. 16, the photodiode bias is not bypassed. Is decoupling to the positive supply only necessary if power supply noise is large?
What's the ideal configuration if power supply noise is not an issue? Would that be package substrate bonded to +Vs, bypass cap attached to signal ground, and no decoupling of the photodiode to the positive supply? I'll be including the bypass cap C1 inside the TO package, but I'd prefer not to fit the bias decoupling network inside the can (they can be on an external PCB, if needed). If it matters, the bandwidth I'm shooting for is relatively modest (~150 MHz), and the photodetector I plan to use has a fairly large capacitance (~5 pF).