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Driving ADC AD7631 using AD8421 and AD8271

Question asked by jebaspaul on Jan 20, 2014
Latest reply on Jan 22, 2014 by jebaspaul

Hi,

 

Please refer the attachment for schematic.

 

I am working on multi channel Data acquisition system. Each channel is sampled and quantized in 25 us.

 

AD7631, 18 Bit ADC, is used in this design. As per the information given in the ADC datasheet, a RF filter is needed in front of ADC. It has R(12ohm) and C(2.7nF). Currently, there is no buffer placed in between IA and ADC. The ADC is driven differentially using AD8421 and AD8271(IA reference generator). I can see some overshoots at the output of IA in simulations. And also in AD8271 datasheet, it is mentioned that the series resistance should be greater than 20 ohm.

 

Qns:

1. Can AD8421 and AD8271 drive AD7631 [ RF filter(R=12 ohm & C =2.7 nF) ] without any stability and settling time issue ?

2. Is that RF filter in really needed in front of AD7631.

3. The buffers suggested for driving AD7631 is costly. (AD829AQ - $5.5). Can anybody suggest a low cost buffer.

 

Note:

Supply voltage - +/-15V

Input signal - +/-10V

 

Thanks,

Jebas.

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