What is the difference between AD7608 and AD7609 inputs? The block diagram for both parts look the same, but there must be something that makes one part a single-ended and the other part a differential input. What is it?
All we have are the datasheets and a circuit note on layout considerations. Calibration routines are different for each device and they are optimized for the input conditions specified. Using the AD7609 as a single-ended part, for example, would not show optimum INL or THD.
We have parts with programmable unipolar/bipolar single-ended or differential ranges though, if you want to check them out.
The AD7608 and AD7609 are from the same family of high resolution, bipolar input, simultaneous sampling DAS solutions, thus they share the same architecture, and have similar functional block diagram. This family of DAS solutions differ in their inputs, resolution, and number of channels. The AD7608 and AD7609 are both 18-bit, 8-channel ADCs but the AD7608 accepts single-ended inputs while the AD7609 accepts true differential inputs. If you look at the block diagram and analog input section of the datasheet, you’d notice that the AD7608 have VxGNDs while AD7609 have Vx-s.
Let me elaborate.
The AD7608/9 perfectly fit into our application. The only drawback is that we need to build separate variants for single-ended and differential inputs – a problem that is apparently present for other users as well (like here http://ez.analog.com/message/124945#124945).
The input structure for both devices seems to be the same (some sort of differential buffer, as seen in the block diagram), but the AD7608 accepts only single-ended inputs (with a pseudo differential kind of input, since VxGND is allowed to float a little bit) and the AD7609 accepts only differential inputs (with a relatively wide common mode range, but not wide enough to “misuse” the differential input as single-ended input). All in all the input properties would call for a device that can do both, single-ended and differential input, based on a range setting or so.
But maybe the AD7608 and AD7609 aren’t that similar, and show some essential differences on their input buffers. I would like to understand what these differences are.
Maybe there some circuit or app notes that cover this topic?
I hoped for some academic insight , but we'll stick with the AD7609 anyway. Other parts like ADAS3022 have other trade-offs.
Thanks & regards,
Retrieving data ...