ADS8867 diff mode ADC input signal?

[opampsmoker]

Hi
Do you know what is the input signal being digitised by the schem on page 30 of the datasheet( fig 60).
Howcome there are two signal sources?

ADS8867 datasheet

https://www.ti.com/lit/ds/symlink/ads8867.pdf?ts=1605112692262&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FADS8867

 

[gophert]

Howcome there are two signal sources?

Because it is a differential ADC. It measures the difference between two signals. As in one non-zero reference voltage and a signal voltage or the difference between two signals. One signal can be at ground but then you could have selected a standard ADC.

 

[opampsmoker]

Thanks, please could readers also advise on the circuit on page 33, fig 63 of the ADS8867 datasheet.?..this shows a diff amp buffer in front of the ADS8867.....surely if you have a diff amp buffer right at the ADC input...then you dont need a diff mode ADC chip like the ADS8867?

Or does the THS4521 go near the signal source, and then the diff pair runs however many cm's to the ADS8867, which just has the little RC filter in front of it.?

 

[ChrisP58]

Thanks, please could readers also advise on the circuit on page 33, fig 63 of the ADS8867 datasheet.?..this shows a diff amp buffer in front of the ADS8867.....surely if you have a diff amp buffer right at the ADC input...then you dont need a diff mode ADC chip like the ADS8867?

Or does the THS4521 go near the signal source, and then the diff pair runs however many cm's to the ADS8867, which just has the little RC filter in front of it.?

Go back a few pages and read the section called ADC Input Driver starting on page 28.

But yes, if you've got a differential amp as the front end, you may not have any benefit from a differential ADC. That all depends on what your system needs are.