AD9656 input configuration

dhslichter commented 7 years ago

[ ] 1. Use Schottky diodes for input protection on AD9656. For each input, want diodes both to ground and +1.8V supply rail. Diodes should be placed immediately next to AD9656, between AD9656 and filter/impedance matching component footprints. Suggest HSMS-286C-TR1G, which has low forward voltage and tolerates up to 4V reverse bias. Series connected diodes, series anode to ground, cathode to +1.8 V rail.
[ ] 2. Include 0603 pads for impedance matching/band defining components TBD. Input impedace information for AD9656 available here in Excel spreadsheet form to enable component choices. See also AN-742 and AN-827. Connections should be differential only, no connections to ground or positive rail. See drawing below.

jordens commented 7 years ago

What about ESD protection (i.e. some nice TVS)? Do we leave that to the mezzanine?

hartytp commented 7 years ago

I'd leave that to the mezzanine -- there are going to be relatively few cases where the input signal is coupled directly into the ADC, so protection will be needed upstream...

jordens commented 7 years ago

@hartytp ack @dhslichter the lower diode needs flipping...

dhslichter commented 7 years ago

TVS is a disaster from a distortion standpoint, so we leave that decision to the mezzanine designers. RF Schottky gives protection with minimal distortion. @jordens good catch on diode directions, was distracted as I posted initially, have updated top comment to fix.

dhslichter commented 7 years ago

Further information on TVS vs Schottky for ADC input protection: http://www.analog.com/media/en/analog-dialogue/volume-49/number-2/articles/rf-samp-adc-input-protection.pdf

dhslichter commented 7 years ago

@sbouhabib please add any comments/thoughts here.

sinara-hw / sinara

AD9656 input configuration #38