Instrumentation amp question

[Speakerguy]

I'm designing a multichannel data acquisition system, mostly for thermocouples and other temperature sensors. I would like the front end to be composed of identical subcircuits for each channel that are identical, with the functionality of each block determined by selectively populating and depopulating certain components. Doing this for the various sensor types I have using an instrumentation amp is pretty easy.

There is a special case where I have to deal with pure analog inputs (lets say a zero to five volt signal) and an ADC with a 0-5V input range. I would like to use an in-amp for this as well, tying the inverting input of the in amp to ground, connecting the noninverting terminal to the input signal, configuring it for a gain of one, and just sending it to the ADC. Essentially just using the in-amp as a buffer. However, it seems a lot of in-amps don't like this if setup for single supply operation (input common mode not extending to the negative rail).

Is what I am proposing ill advised, or do I just need to be careful about the selection of the in-amp? If so, does anyone have a recommendation for an in-amp that would be capable of this? Bandwidth is not a big concern, low power consumption is. Also has to be unity gain capable for the buffer thing. Thanks for any help!

 

[Winterstone]

I would like to use an in-amp for this as well, tying the inverting input of the in amp to ground, connecting the noninverting terminal to the input signal, configuring it for a gain of one, and just sending it to the ADC. Essentially just using the in-amp as a buffer. However, it seems a lot of in-amps don't like this if setup for single supply operation (input common mode not extending to the negative rail).

Hi Speakerguy,
For my opinion it should work (single supply) - provided that
*both inputs are referenced to Vcc/2 (instead of ground potential), and
*the (grounded) resistor of the 2nd amplifier also is referenced to Vcc/2.
Then, a unity gain configuration is achieved by removing the gain setting resistor at the input (R>>infinite).

W.

 

[crutschow]

The are numerous rail-to-rail type op amps that work fine with a single supply as a unity gain buffer. If you Google "rail rail low power op amp" you will get a number of hits.

 

[Gayan Soyza]

My favorites MCP619 & MCP6042.