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ADCs with minimum voltage reference

Darrell Rivers
Prodigy 70 points

Other Parts Discussed in Thread: ADS7866, ADS1114

Hello!! I am looking to measure very low voltage signal (0-0.5V range) and was wondering if it is possible without amplification. Hence I would like to know what's the minimum voltage reference of ADCs available at TI. Looking at a few datasheets, it seems to be 1.65V...however, if ADCs(10 or 12 bit) are available with a reference lower than that please let me know. 

  • 0
    TI__Guru**** 182551 points

    Hi Darrell!

    Welcome to our e2e forum!  Not sure which part number you were looking at, but I'm curious to know why you don't want to boost up the signal a little.  Can you tell us a bit more about your project and which ADC you were looking at?

  • 0 in reply to Tom Hendrick
    Prodigy 70 points

    I am looking to amplify load-cell bridge output. The main target is to form a low cost and simple solution so looking to get rid of the amplifier if possible. So far the lowest reference I have found is ADS7866 with 1.2 Vref. I would like to know if there are any particular problems of using a low reference if signal is low.  

  • 0 in reply to Darrell Rivers
    TI__Guru**** 182551 points

    Hi Darrell,

    Have you looked at the ADS1114?  There is a PGA internal to the device, so you wouldn't need an external amplifier.

  • 0 in reply to Tom Hendrick
    Prodigy 70 points

    I might have to end up using ADCs with PGAs but I was trying to explore the possibility of not using one. But thanks anyway!

    Darrell Rivers said:
    I would like to know if there are any particular problems of using a low reference if signal is low.  

    Could you please answer this? I don't think there could be any problems, in fact it would offer better resolution right?

  • 0 in reply to Darrell Rivers
    TI__Guru**** 182551 points

    Hi Darrell,

    The main issue is noise.  With a 12-bit device and a 1.65V reference (assuming 0-Vref is the input range of the ADC), you have a 403uV LSB size.  The ADS7866 will most likely need to be driven from an amplifier in order to properly settle the input voltage to within +/-1/2 LSB during the acquisition cycle (see Analog Input and Choice of Input Driving Amplifier on page 19).

  • 0 in reply to Tom Hendrick
    Prodigy 70 points
    Tom Hendrick said:
    The main issue is noise.

    Which noise are you referring to specifically? The inherent noise of the ADC or from the bridge circuit? Won't using an amplifier amplify the noise by a proportional amount as well leading to the possibility of it not settling within the LSB.

  • 0 in reply to Darrell Rivers
    TI__Guru**** 182551 points

    Hi Darrell,

    All of the above, plus whatever noise might be on your power supply as that is used for the reference in the ADS7866.  Yes - noise from the bridge would be amplified by an amplifier tied to the ADS7866, but depending on the amplifier used it wont really have a big impact on settling time.  Settling time to the input of the ADC is primarily based on the amplifiers bandwidth.