AD8330 with AD8131

Question

Hi everyone. Sorry for my english. Please try understand me:) I have a problem with AD8330.
I'm designing a DIY digital oscilloscope. I want to use a typical double j-fet circuit in input.
The j-fet are powered by +/-5V. Next AD8131 (+/-5V) are driving VGA AD8330(+5V). On all schematics I have
seen that the AD8131 has a two resistors: 24.9 and 49.9 ohm. My question is...can I connect the
inverting input to global ground and non inverting input trought the output j-fet without those resistors?
In my circut I can't connect the 49.9ohm resistior to ground, it's too big load for J-FET.

EZAdministrator · Accepted Answer

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Thank you,
EZ Admin

ADIApproved · Answer

Hi, 
 Could you post a schematic so I can see how you plan to connect the two FETs? 
 An alternative to discrete FETs is to try the ADA4817-1 FET-input op amp for your oscilloscope front end. 
 If you are trying to design a differential front end then use two of them with the AD8129/AD8130 as the third amplifier to 
 make a high speed instrumentation amplifier. Or the older AD830, which should also work and has a more detailed data sheet. 
 Use this to drive the AD8337 VGA. 
 Regards, 
 Bob

Electronic Design Services - PartnerZone

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AD8330 with AD8131