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Which ADC to use?

Other Parts Discussed in Thread: ADS1258, ADS131E08, ADS130E08, ADS1278, ADS1178

hello guys,

i'm a student at JCU, I'm currently working on a project where i'm trying to build a data logger that logs from 12 differential inputs (strain gauges). I need an external ADC chip that can log concurrently at 2KHz and can take and amplifies differential input (as for strain gauge). This ADC should be able to send data via SPI or I2C to a micro controller for further calculation. I'm asking about which ADC to use, as i am very new to using an external ADC ( usually use the ones that come in a micro controller). I looked at many of TI ADC chips and many other companies ADC chips, but finding it very hard to find one that fit my need. if you have worked with external ADC chips, please advice me on any info that you might know of and if possible the circuitry that they need. Sorry about the terrible writing ( writing this at 4:43 in the morning)

cheers

Abdul

  • Abdul,


    I think there's a bit more information that we'd need to make a recommendation. Do you need the channels to simultaneously sample? or is it ok if they are sampled concurrently. What sort of resolution do you need? Are all of the inputs measured with the same reference voltage?

    If the inputs we're single-ended, I would have thought an ADS1258 might work. This device uses a 16 input multiplexer and you can take consecutively from each of the channels.

    However, if you need simultaneous samples, I think you may need two devices of either the ADS1278, or the ADS131E08. Both are 24-bit ADCs (note that the noise depending on data rate will affect the equivalent resolution). These devices both have 16-bit equivalents in the ADS1178, or the ADS130E08.


    Joseph Wu
  • hey Joseph, 

    thanks for the reply and sorry about the little information. I do need the ADC to sample all inputs at the same time, about 16 bit resolution should be fine, what do you mean if they all measured with the same reference voltage?

    Abdul

  • Abdul,


    If you need 16-bit performance and simultaneous sampling, I'd choose the ADS1278, or the ADS131E08.

    As for the comment on the reference, I was just checking to see that all of your measurements absolute voltage measurements (as an example, you set a particular reference like 2.5V and make a measurement). In some systems, you can use multiple references either different voltages, or you could use a voltage measurement and a ratiometric measurement. A ratiometric measurement would be using a single excitation current to drive an RTD (resistive temperature detector) and a known precision reference resistor. The output code would be a ratio between the RTD resistance, that you are trying to determine and the reference resistance, which is known. In this measurement, you never use the use a voltage in the conversion.

    I'm guessing that if you don't need to do a ratiometric measurement, you'll be ok with a single voltage reference.


    Joseph Wu