Chosing voltage reference for MCP3913 ADC

[Vex]

Hi everyone,

I'm having trouble understanding how to connect the voltage reference to the MCP3913 (http://ww1.microchip.com/downloads/en/DeviceDoc/MC93913-Data-Sheet-DS20005227B.pdf).
I have to connect a bipolar signal +/- 1V, with respect to AGND, on all 6 channels. VREF pin of the ADC can't be connected to the voltage lower than -0.6V with respect to AGND. How can the ADC measure -1V then?

[iMo]

The ADC inputs are "differential". Also both IN+ and IN- should stay within AGND and AVDD.
An example:

IN+   IN-     result

2.0    0.8     1.2
1.5    1.5     0.0
1.0    1.5     -0.5
0.3    2.4    -2.1

[AE7OO]

Actually in this case the MCP3913(Like the MCP3911 which I use) can measure +/- .6V referenced to AGND.  Max input is +/- 2V, but signals outside of the +/- .6V range won't be very accurate.  They do caution about holding inputs below AGND for any length of time, or if the internal clock is not running.

As far as the voltage reference goes, what kind reference are you using that has better specs(9ppm/C  tempco) than the internal?   Beating the internal VREF is hard because at that level everything counts, how long your traces are, how clean the board is, solder type, etc.  These are not like some MCU vrefs that might have a 500ppm/C tempco or worse, where adding even a $2.00 external reference makes a big difference. 

[AngélicaMX]

Even using the internal reference, can the MCP measure negative voltages of up to -0.6V?

We don't need to put any negative sign in the REF-?