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ADS1298 with data rate of 600sps.

Gabriel Rozenwald
Prodigy 20 points
Other Parts Discussed in Thread: ADS1298, ADS1271, ADS1298ECGFE-PDK

Hi,

I am considering the ADS1298 for an ECG equipment that would be used where the mains frequency is 60Hz, thus the sampling frequency of 600Hz would greatlly simplify the design of the mains notch filter (already done). According to the datasheet the CLK frequency should be 2,4576 MHz, thus, above the maximum of 2,25 MHz  listed for the external clock reference.

We also already have a family of products that runs on the ADS1271 with 600sps and all the ecosystem of software expecting this data rate.
I believe the ADS1298 is a great product but overseeing the need for other data rates, as 600sps, was bad businness strategy in my humble opinion.

So, is it possible to overclock the device to achieve a 600sps data rate?

 

Thank you for your kind attention.

Gabriel Rozenwald

 

  • 0
    TI__Guru**** 180931 points

    Hi Gabriel,

    Welcome to the e2e forum!  Thank you as well for you honest opinion on the ADS1298! 

    The clock limits in the data sheet are there to show the frequency range of the main modulator clock we've used to verify all performance parameters of the ADS1298 over the specified operating voltage and temperature conditions.  Running the clock up to 2.4576MHz would be outside the specified operating limits of the ADS1298 as you noted above.  You could implement 50/60Hz Notch filters in software using the published ADS1298 data rates, would that be a possible option?

  • 0 in reply to Tom Hendrick
    Prodigy 20 points

    Hi Tom,

    Thank you for your prompt response. The point with the notch filter is that the 600Hz enables the design of a digital filter with a theoretical infinite attenuation of the 60Hz, only affected by the quantization errors. So, the filter is already made in software, however it only work if the sampling rate is multiple of the notch frequency (60Hz).
    The other point is that we would like to co-exist with already deployed software that expects 600sps.

    I am considering buying the development kit, but I would like to know if there is something that is not expected to work if I  try driving the clock at a different rate (possibly slower, say 1,2288 MHz) that could yield the 600sps.  I am asking this because I noticed that this a brand new product and may be there was not enough time to perform a full product characterization  outside of the default clock range (just guess work here).

    Thank you for your king attention.

     

    Gabriel Rozenwald

  • 0 in reply to Gabriel Rozenwald
    TI__Guru**** 180931 points

    Hi Gabriel,

    The ADS1298ECGFE-PDK hardware has a 3-pin jumper (JP22) that allows you to select an external modulator clock.  The default setting for this jumper is closed pins 2-3 which selects a 2.048MHz oscillator installed on the board.  If you move the shunt on JP22 to cover pins 1-2, you can apply an external modulator clock source on J3 between pins 17 (clock) and 18 (ground) or directly to pin 2 of JP22 referenced to one of the ground test points.  There is nothing I am aware of that would not be expected to work.