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ads1293 R1/R2/R3 settings affect output amplitude?

user4366959
Prodigy 50 points
Other Parts Discussed in Thread: ADS1293

Dear Sirs,

I observed following phenomenon by changing R1/R2/R3 parameters. Could you tell me the mechanism of this phenomenon?

Test condition

VDD:3.3V, 1.65V+-0.4V sine wave (1Hz) to Ch1 posi input and 1.65VDC to Ch1 nega input.

R1      R2      R3        ADC max (from spec)       Ovserved

4          4        16         800000h                              Output is clean sine wave with 22.7bit output range <- this is good

4          8      128         800000h                              Peak is satured by 800000h

SN/BW should be affected by decimation rate, but I cannot understand why the decimation rate affects output level.

Best regards,

Yukio

 

  • 0
    TI__Expert 3350 points
    R1, R2, and R3 are bits to program the bandwidth of the channel. They determine the decimation ratio of the SINC5 filters placed after the sigma-delta modulators to filter the oversampled data from the modulator. Please see page 17 of ADS1293 datasheet. What you are observing is the effect of the particular filter setting on the signal.
  • 0 in reply to Bahram Mirshab
    Prodigy 50 points
    Dear Mirshab-san,
    Thank you for your reply. I understand your comment, but still cannot find the mechanism why the output
    offset is affected by the R1/R2/R3 settings even if it has same 800000h max ADC output range.
    By the way, I was hit by another phenomenon when I used ADS1293 software tool. Below setting 1 and 2 is
    the portion of captured data with two different settings of R1/R2/R3 parameters.
    My question is
    Q1: In case of setting 1, time stamp starts from 2.000000. In case of setting 2, time stamp starts from
    0.000000 and this should be normal.
    Q2: Relating to Q1, setting 1 logged only 2secnds data, not 4 seconds. Setting 2 can capture 4 seconds
    data.Above phenomenon happened 100% based on the setting 1.
    Could you tell me if this comes from that my usage is incorrect, or from the software bug?
    Setting #1R1:4 R2:4 R3:163leadCapturing time: 4seconds
    ----------------------------------------------------Curve: ECG CH1, size: 794
    Index, Time [Seconds], Output Code
    ----------------------------------------------------0, 2.000000, 4176584.000000
    1, 2.002500, 4176695.0000002, 2.005000, 4176876.000000...
    791, 3.977500, 4176466.000000792, 3.980000, 4176564.000000
    793, 3.982500, 4176683.000000End of CH1 dataSetting #2R1:4 R2:5 R3:6 3lead
    Capturing time: 4seconds----------------------------------------------------
    Curve: ECG CH1, size: 3412Index, Time [Seconds], Output Code
    ----------------------------------------------------0, 0.000000, 6049170.000000
    1, 0.001172, 6049108.0000002, 0.002345, 6049059.000000...
    3409, 3.996483, 6048739.0000003410, 3.997655, 6049052.000000
    3411, 3.998828, 6049091.000000End of CH1 dataBest Regards,Yukio
  • 0 in reply to user4366959
    TI__Mastermind 21685 points

    On the "Measurement" tab, the "Capture Mode" can be set to "Run Continuously" or "Acquire" mode. When "Run Continuously" is selected only last 2 second of data is saved. If "Acquire" is selected, user can save up to 60sec of data. Thanks. 

  • 0 in reply to Vishy Viswanathan
    Prodigy 50 points
    Thanks, Vishy-san, but...
    The setting is "acquire" with 4seconds for both capturing data. Difference is just the R1, R2, R3 setting. Captured data of setting #1 R1:4 R2:4 R3:16 starts from time stamp 2.0000 and period is 2seconds. Data of setting #2 R1:4 R2:5 R3:6 is OK with 4second data. Why setting #1 cannot capture 4seconds even though I set "Acquire for 4seconds" ?
  • 0 in reply to user4366959
    TI__Mastermind 21685 points

    May be some fault is occurring. Please check all the error registers. Thanks.