Options for positive and negative ADC (Bipolar)

Thread Starter

Edwarddim

Joined May 2, 2019
4
Hi,

I am wanting to create a circuit board with a Bipolar ADC on it and not sure what the best option would be.

I am using an esp32 but wanted to use an external ADC (surface mount) for better accuracy. The range that I want to measure is -2.4V->+2.4V. My first attempt I thought to just use a simple voltage divider, an ADC (ADS1115) and the 3V3 on the ESP32 to boost the signal so I could measure negatives which worked ok but the 3V3 fluctuates a lot with temperature which decreases the accuracy dramatically. I did do some calibration that made it a bit better but I feel it would be much easier to just use a bipolar ADC.

Is getting a bipolar ADC the easier way? What types of bipolar ADC's should I go for? Any specific recommendations? I would like to have 4 channels with mV accuracy if possible.

Sorry if I am asking a stupid question or it has been asked before. I did search the forum and couldn't find anything.
 

Delta prime

Joined Nov 15, 2019
576
Hello there :)
An onboard•INTERNAL PGA is available on the ADS1114 and ADS1115 that•I2C ™ INTERFACE: Pin-Selectable Addresses offers input ranges from the supply to as low as±256mV.
 

crutschow

Joined Mar 14, 2008
25,660
I could measure negatives which worked ok but the 3V3 fluctuates a lot with temperature which decreases the accuracy dramatically.
You could use a reference voltage IC to generate a stable reference. such as the LT1634 or, the somewhat less stable TL431.
(What are your stability requirements?)
 

Thread Starter

Edwarddim

Joined May 2, 2019
4
There are many variations of ADC input configurations so what type of bipolar ADC do you really want?

https://www.analog.com/media/en/new...ection-guide/Precision-ADC-Selector-Guide.pdf
Had a look there and I guess I am looking for either a Single-Ended True Bipolar or a Pseudo-Differential True Bipolar. I can't see on this list any that are 3.3V supply and multi channel?

You could use a reference voltage IC to generate a stable reference. such as the LT1634 or, the somewhat less stable TL431.
(What are your stability requirements?)
I have kind of figured out the problem for the circuit that I was using and it turns out that it wasn't the supply 3V3 that was fluctuating with temperature but the protection diodes that I was using which was causing the fluctuations with temperature. Removing them fixed the issue so I should be able to keep using it and think about something else for protection.

Thanks for the help however I am still keen to find out if there is a much simpler option.
 
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