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Differential Op-Amp to Differential ADC

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hanua

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Hi guys,

New to the forum and it seems I have some question regarding using an op-amp to present a real word input to a differential ADC.

I'll present some information of the time of input I want to be sampling. The input comes from a detector which has negative going pulses with rise times from 20-40 nsec, falling times around 100 nsec. Pulse amplitudes are from -20 mV to -100 mV. Basically what I want to do, is to use the op-amp to AC couple the detector input to the ADC and have the pulses taking up the whole range of the ADC.

The ADCs I'm using will be the ADS62P28/29/48/49. All of these are interchangeable as long as I have the proper connections made on the board. Output from the ADC will be to a FMC connector on a FPGA board.

The part I'm not really confided is the configuration of the op-amp to ADC since i've never worked with this before.

I'll post some schematics of what I have so far. op_amp_input.jpg
This first one is the input from the BNC connector to the op-amp. Right now, I have it configured for a differential gain of 1.

I understand that I basically need to take the input signal range, amplify it and shift it into the input range of the ADC. Which I believe is the job of the op-amp. I've seen so many configurations of op-amps which seem to do the same thing that I'm just confused now.

This is the ADC configuration.
adc_input.jpg

The ADC input range seems to be 2Vpp. What does this mean? Is this between +1 V to -1V for what does it mean? Also what is the purpose of the Vcm and how does it need to be connected between the op-amp and ADC.
 

dear the things you explained are not so clear, please define the op-amps output clearly so that we can work on it.
 

dear the things you explained are not so clear, please define the op-amps output clearly so that we can work on it.

Would you please explain what I need to re-define on the schematic. I've used nets to link between schematics.
 



I've changed the analog input a bit using a new op-amp. Is this circuit properly balanced and AC-coupled?
 

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