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"Comparing SAR and delta-sigma ADCs' throughput times", EDN, 4/22/2010

Bonnie Baker - WEBENCH Design Center
Expert 3555 points
Other Parts Discussed in Thread: ADS1256, ADS1258, PGA280, ADS1259, OPA365

From: Feng

Dear Bonnie,

I read your article about “Comparing SAR and delta-sigma ADCs’ throughput times” in latest issued EDN. In fact, I’m in similar situation now. I’m planning to use TI 8 ch, 24 bit, 30kSPS, with internal PGA, ADS1256 for our new data acquisition system. Also, I was thinking to use TI ADS1258 (16 ch, 24 bit, 125kSPS), plus external PGA280. It seems the later selection will give us better performance (sampling speed and more channels), but I’m not sure the combination(ADS1258with PGA280) will give us better results compare with ADS1256. So, for safe the ADS1256 maybe is a better choice?

Looking forward your comments or suggestions.

Best regards,

Feng

---------------------------------------------

Feng,

We don’t have anything on this particular application. However, the PGA280 has been paired up with the ADS1259 which is a much slower sampling device (under 1MHz). The ADS1258 samples at about 8 times higher and may require a faster amplifier as a buffer.

I know that one of our applications engineers has recommended the OPA365 as a buffer, which has a UGBW of about 50MHz which may preserve the linearity and gain error. In the PGA280, the gain bandwidth product is about 6MHz (above G=4) and it might be slow.

 Bonnie Baker

  • TI__Expert 4630 points

    Hi Feng,

    from my experince I would expect that the ADS1256 gives you better performance. However a good and easy possibility for you could be to use ADC Pro and the EVMs  to find the better solution. That's what I would suggest to my customers to do for the comparison above. In addition they get a real statement what precision they can achieve in their design.

     

    Best wishes,

    Olrik

     

  • in reply to Olrik Maier
    TI__Expert 3555 points

    Feng and Olrik,

    You have to be careful when you use the term "better performance". In terms of performance, what are you talking about? is it accuracy (the DC specs like offst, gain, INL, DNL), repeatablity (the AC specs such as SNR, noise, and THD), or throughput time? And to take this a bit further, there are other considerations in terms of performance such as power, power supply values, temperature range, settling time, etc. But your last suggestion is good. I think an evaluation is in order. Before you start on your evalution of the hardware, go into it with open eyes. Take a look at the data sheets of all of the products in your signal chains and try to get a good feel for how your bench evaluation will go.