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ADS1259: adjust reference voltage to input range

pavel panteluk
Prodigy 110 points
Part Number: ADS1259
Other Parts Discussed in Thread: REF6241, REF6250

I need to digitize differential signal +-3.6 V. to get better precision VREF have to be close to 3.6 V. My reference have 2.50 V. What the best way to do this? Use operational amplifier to gain my reference voltage, use operational amplifier to suppress my signal or use reference with bigger voltage source and then suppress it?
And second question. can i use one power supply and reference voltage source to many (3-6) ADC ?

  • 0
    TI__Guru**** 168605 points
    Hi Pavel,

    Can you give us a little more information on your input signal? Is it a bipolar +/-3.6V signal or is there some DC bias to it? The max AVSS of the ADS1259 is -2.8V, so if your signal is truly bipolar, you would need some level shifting and it might be easier to attenuate the signal at that point.
  • 0 in reply to Tom Hendrick
    Prodigy 110 points

    So, my sensor has defferential output, positive output and negative one. Between ground and positive or negative output always non negative voltage, between positive output and negative output voltage in range -3.6 to +3.6 (and it's not periodic AC)

  • 0 in reply to pavel panteluk
    TI__Mastermind 44550 points
    Hi Pavel,

    The ADS1259 can measure differential voltages up to +/- Vref. Therefore, your reference voltage will need to be at least 3.6V, but I see no issues with using a larger reference, such as 5V.

    I would recommend using a low-noise reference, such as the REF6241 or REF6250. These references have buffered outputs and would be better suited for driving multiple ADC reference inputs. A benefit of using the REF6241 is that you could use the same 5V supply for both the ADC and reference ICs.

    I would not recommend gaining up the reference voltage, if given the choice. Adding an amplifier to the circuit adds additional noise and error (such as offset, gain, and drift errors). Also, since this is a 24-bit ADC with thermal noise that is larger than the ADC's LSB size, there is no benefit or additional resolution that can be achieved by using a smaller reference voltage (1 LSB with a 5V reference is below the noise floor, so making the LSB size even smaller will only increase the number of unstable bits)

    ...That being said, the input to the ADS1259 is unbuffered, so if your signal is not buffered you will need to add an amplifier to the input of the ADS1259, and in this case it may make sense to gain up your input signal to the same amplitude as your reference voltage.
  • 0 in reply to Christopher Hall
    Prodigy 110 points

    Thank you for your full and exact answer again. It is big help in my project implementation, especially in such field that requires experience rather than specification data knowledge.

  • 0 in reply to pavel panteluk
    TI__Mastermind 44550 points

    Glad to help! Let us know if you have any additional questions.