# Ranges for ADC Reference Voltages

I am trying to select and ADC with single ended inputs which can input positive and negative voltages (around +500mV to -500mV). Due to the nature of the system I am selecting it for, the voltages cannot be DC biased and also cannot be amplified (in other words the exact DC level is the information). I was wondering if it would be possible to set the reference voltages to REF+ = 500mV and REF- = -500mV, while the power supply is 2.5V to -2.5 V (the ADC allows for true bipolar operation). For instance the ADC I am looking at is an Analog Devices AD7176-2. I noticed in the data sheet that the limits for the reference is that their total voltage difference can be 1V, but the tests they have are only for +5 V to Ground supply, not bipolar operation. Hopefully someone has experience with operating an ADC in this mode. Thanks

• Working with 24-bit ADCs isn't easy. A question that comes to mind is, Why not just use the device's internal reference? With fully-differential inputs, you don't need to keep the inputs strictly within the VSS-to-REFOUT range. Commented Mar 24, 2013 at 16:29
• Well, could you elaborate? DC voltage is the output of my system and it can range from positive to negative. Also the internal reference would be higher, I think it is 2.5V so your voltage step size would be 2.5V/(2^24). If I could just make it within the limits of my output then I would only have 1V/(2^24). Basically I am looking for a way to resolve the exact DC level (positive and negative), very small values, with high precision. (World's best ADC haha) Commented Mar 24, 2013 at 16:38
• My concern is, it will be very difficult to generate your -0.5 to +0.5 V reference with 24-bit accuracy...maybe you will lose as much precision from errors in your external reference as you do from having 2.5 V instead of 1.0 V reference. At the same time you add expensive high-precision external parts for the 1.0 V reference, and also increase the risk of a design error due to added complexity. Commented Mar 24, 2013 at 16:42
• I was concerned about that too, but that's where these components come in: analog.com/static/imported-files/data_sheets/ADR130.pdf Commented Mar 24, 2013 at 16:46
• Not bad. AD7176-2's reference has better initial accuracy and tempco, but ADR130 does win on long term stability. Commented Mar 24, 2013 at 16:53