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ADS131M08: Is this a precision ADC too?

Bela Istvanfi
Prodigy 30 points
Part Number: ADS131M08

Dear experts,

I'm planning to use ADS131M08 in a precision multi-channel instrument. Its basic data (resolution, output data rate, Delta-Sigma architecture, synchronous sampling) are the deciding factors.

As I study the documents, You are recommending this ADC for energy measurement applications. My application is not that, I need a precision ADC to digitize the output signal of a photosensor, in a laser-interferometry application.

This is my first practical use of D-S converter, and I have the following two questions:

1. Have You got any arguments against this ADC? Can You recommend a better one ? Which is also available, I mean.

2. According to Mr Shannon: is the input sample rate Fclk/2? In case of 8MHz clock, the input sample rate is 4MHz, therefore I can create an antialiasing filter with this parameter and _not_ with the output data rate. Is this correct, or am I wrong?

Thank You in advance and Yours sincerely:

Bela

  • 0
    TI__Guru**** 168605 points

    Hi Bela!

    Welcome to our e2e forum!  Welcome to the world of delta-sigma converters as well! 

    For your first question, the AMC131M08 is a great part!  If you can tell use some features that you are looking for, we might be able to point you to another device.  Do you need 8 simultaneously sampled inputs?  What data rate are you looking for?  What sort of dynamic range?

    For Q2, you are close.  The ADS131M08 divides the clock by 2 internally which sets up the actual sample rate and then Table 7-1 shows you the various OSR options with their effective data rate.  Here is a nice blog post that you might find useful:

    https://e2e.ti.com/blogs_/archives/b/precisionhub/posts/the-delta-sigma-advantage-to-anti-aliasing-filters

  • 0 in reply to Tom Hendrick
    Prodigy 30 points

    Hallo Tom,

    thank You for the answer, and excuse me for the delayed reaction. I wasn't around my computer for a few days.

    So, the features I'm looking for:

    - Simultan sampling is essential, since we're converting 16 channels and the timing of the output data is critical. Should be simultaneously sampled, due to the nature of our measurement. I am planning to use 2 pcs of ADS131M08, supplied with the same clock and there's the reset/Sync input, hopefully it provides synchronisation between the chips as well.

    - Data rate: at least 20 thousand conversion per second. Can be higher too, while we're using a powerful uC as interface between the ADC and the computer. (A PC is on the top of the whole system, it receives the conversion data after applying some math in the uC)

    - Dynamic range: Unfortunately I cannot provide this in dB. The higher the resolution is the better, I am planning 24 bits. Since the noise is also critical - who needs the lower bits as a random number generator? - I'd like to remain in the Delta - Sigma architecture. I have some experience with SAR types but not yet with D-S. I hope the D-S is more friendly architecture, due to it's integrating nature.

    - There's another point of view: the availability of the component. Unfortunately it is also a critical parameter today. We could manage to buy some ADS131M08's. Just enough until the end of 2023. They're already here on my desk. We do hope we can buy them later, too.

    Also, thanks for the blogpost!

  • +1 in reply to Bela Istvanfi
    TI__Guru**** 168605 points

    Hi Bela,

    Synchronizing two or more ADS131M08 devices is definitely possible.  If you look over table 7-2, you can get 16 kSPS with an OSR setting of 256 or 32 kSPS with an OSR of 128.  The effective resolution drops as you decrease the OSR (that's the nature of the DS converter).  I'll let Ryan know you enjoyed his blog post!