Delta sigma ADC with gain > 128

Discussion in 'General Electronics Chat' started by Vindhyachal Takniki, Feb 6, 2015.

  1. Vindhyachal Takniki

    Thread Starter Member

    Nov 3, 2014
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    1. I have application where I need to measure strain (quarter bridge three wire) of 120ohm.
    2. This is power sensitive application so I am using small current to excite strain bridge isntaed of voltage.
    As I can switch off current source when not required.

    3. I am using 24 bit adc - ADS1248 with internal current source.
    4. Is there any high precision adc with PGA > 128 ?
     
  2. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    As far as I know, no one makes a D-S A/D with gain > 128. And I use these kinds of parts often (most often, ADS1242).

    You could drop your Vref to as low as possible (0.5V, I think) or add a high-quality instrumentation amp between the bridge and A/D.

    Both solutions will add noise. You can average multiple readings to improve noise performance.
     
  3. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    Joey's right... most ADCs have an internal amplifier that works at up to a gain of 8, and after that they implement "digital scaling" which is nothing more than a specially filtered multiplication of the signal obtained from the gain-8 instrumentation amplifier.
     
  4. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    The PGA in a delta sigma is digital, but it's not "faking" the gain. In fact, the input referred noise level drops with increased gain.

    I use the ADS1242 with 128 PGA, and it works quite well.
     
  5. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    I use an old model by Intersil, an HI7190. I found it difficult to program and use... I'm gonna take a look at that ADS1242 of yours, see if it's an improvement... thanks
     
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