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How to reduce the data rate to increase the averaging, and the noise drops correspondingly in ADS1298?

sand lee
Prodigy 10 points
Other Parts Discussed in Thread: ADS1298

Hi,

This is about ADS1298 question.

I set 001 in DR bits of CONFIG1—16KSPS data rates are used in ECG applications to implement software pace detection, and then average to 500SPS data rates. That means I got a 16KSPS data rate input-peferred noise, as follow Table (ADS1298 datasheet 8.1 Noise Measurements),  It is too large noise. I just want a 500SPS data rate input-peferred noise, but I can’t just set 500SPS data rate in DR bits of CONFIG1, because if I do that, it means I couldn’t do software pace detection anymore.

DR BITS OF CONFIG1 REGISTER

OUTPUT DATA RATE(SPS)

-3-Db BANDWIDTH

(HZ)

PGA

GAIN=6

000

32000

8398

87(917)

001

16000

4193

15(206)

010

8000

2096

3(36)

011

4000

1048

1.5(11.2)

100

2000

524

1(7.5)

101

1000

262

0.7(4.9)

110

500

131

0.5(3.3)

 

So, How to reduce the data rate to increase the averaging, and the noise drops correspondingly in ADS1298?

What should I do 16KSPS average to 500SPS can make the input-peferred noise just like set 110 in DR bits of CONFIG1—500SPS data rates?

Is ADS1298 just use sinc filter (ADS1298 datasheet 9.3.2.4.1 Sinc Filter Stage ) to make it? 

  • 0
    TI__Mastermind 18285 points

    Sand,

    I'm moving your post to the correct forum.

  • 0
    TI__Mastermind 38745 points
    Hey Sand,

    The ADS1298 uses a third order sinc filter to get the response discussed in the datasheet. You're probably never going to get the exact frequency response of the 500 SPS data rate since when the data comes out at 16 kSPS it's already been filtered by the sinc3, but you're on the right track. You could do something similar to what the device does in that for each output from your filter, you could take the average of 32 input samples. Taking the average acts like a low pass filter which will reduce the noise level.

    Alternatively, you could use any digital low pass filter you want that has the right band specifications. There is nothing special about an averaging filter once the data is outside of the device. However, helping you choose the optimal digital filter design is outside the scope of this forum.

    Regards,
    Brian Pisani