Hello,
I was reading the datasheet of the AD7671.pdf and I noticed that there are 4 inputs for this single channel ADC. According to the datasheet, they're hooked up to a resistor network, but I really fail to understand why. Like, why not just bring one pin into the ADC and connect that to the resistor network?

I'm not that well informed regarding ADC arches yet, so if you know of a fine article on this particular choice by AD I'd be much obliged if you'd post the link.

Thanks!

 

hi ball,
The d/s explains the purpose of the 4 inputs, they are used for scaling the input voltage range.
E

 

I suppose it is worth mentioning that in almost all cases in this universe as well as all the others that the answers to such questions are always in the datasheet.

 

I suppose it is worth mentioning that in almost all cases in this universe as well as all the others that the answers to such questions are always in the datasheet.

I was actually more interested in why there are four inputs. I knew that they were connected to resistors. Like, if you have a mux to the capacitors, why not just have a mux to the resistor network? What makes this ADC different from the others that it requires four inputs? Did the designers just forget something, or is there something I'm not familiar with (far more likely), that makes four inputs more desirable than 1?

Maybe I could have explained it better in my OP...

Thanks

 

Look at Table I., show below for the hookup arrangement.



Notice the how the different arrangements require different connections to all four inputs.

 

Forgive me if this is wrong, are they using the four inputs to select an impedance range depending on the intended dynamic range of the input signal?

That's what it looks like to me.

 

No. They are using four inputs to select an input range and an offset.
For an input range of ±10V and an offset of 0 you use the ±4 REF line and configure the signals accordingly.
For an input range of 0-10V you use line 0 V TO 4 REF line and connect the signals as indicated.

Do you see what is going on with those hints?

Go back to figure 3 in the datasheet, make the connections as described and see it that makes gives you some clarity.