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ADS1298R external respiration details

Vsevolod Anisimov
Prodigy 240 points
Other Parts Discussed in Thread: ADS1298R, ADS1298

Greetings,

I have two ADS1298R using an external respiration mode RESP_CTRL[1:0] = 0x01. The modulation and demodulation signal are at GPIO pins. The question is could i turn internal demodulation circuitry on? Or in this mode external demodulation is only possible ?

The second question is can i make a modulation signal phase shift between my two ADS1298R?

Best regards,

Vsevolod

  • 0
    TI__Mastermind 38745 points
    Hello Vsevolod,

    You are able to use the internal demodulation circuitry by configuring the device with RESP_CTRL[1:0] = 0x3. Section 9.3.1.7.8.3 on page 47 of the datasheet describes this functionality. Making different phase shifts for the different devices would require two different blocking signals which you would have to generate.

    Regards,
    Brian Pisani
  • 0 in reply to Brian Pisani
    Prodigy 240 points

    Ok, but i must keep GPIO3 and GPIO4 as outputs to drive my external modulation circuitry. As i can see in a datasheet it will no longer be possible. Am i right?

  • 0 in reply to Vsevolod Anisimov
    TI__Mastermind 38745 points
    Vsevolod,

    If you are using the internal circuitry to create a modulation clock and to demodulate, then I recommend you simply use the RESP_CTRL[1:0] = 0x2 option where the excitation signal is both generated and demodulated by the ADS1298R.

    Brian
  • 0 in reply to Brian Pisani
    Prodigy 240 points
    Ok, so as i can see i must provide modulation and blocking signal from external source. And do i have to provide external demodulation signal in this mode? Any phase shift between modulation and demodulation signals? Are there any recommendations for characteristics of external signals?
  • 0 in reply to Vsevolod Anisimov
    TI__Mastermind 38745 points
    Hello Vsevolod,

    Perhaps I was not clear. I am recommending you use the internal modulation and demodulation circuitry. Is there some reason you cannot use this feature?

    Regards,
    Brian Pisani
  • 0 in reply to Brian Pisani
    Prodigy 240 points
    Hello Brian,
    Actually i want to use external modulation and internal modulation both driven by external signals. Is it possible in RESP_CTRL[1:0] = 0x3 mode?
    Best regards,
    Vsevolod
  • 0 in reply to Vsevolod Anisimov
    Prodigy 240 points
    Sorry, of course external modulation and internal DEmodulation
  • 0 in reply to Vsevolod Anisimov
    TI__Mastermind 38745 points
    Hello Vsevolod,

    You previously stated that you needed the GPIO output pins to drive your external modulation circuitry. However, if you're going to use the GPIOs to output the modulation clock, this means that your frequency of modulation is some integer divisor of the ADS1298's master clock. My question then is if your modulation clock is generated by the ADS1298 and you wish to use the ADS1298 to demodulate the resulting signal, what is preventing you from simply using the modulation signal that gets generated at the RESP_MOD pins when you configure RESP_CTRL[1:0] = 0x2? I am just having trouble understanding why you cannot do this.

    Regards,
    Brian Pisani
  • 0 in reply to Brian Pisani
    Prodigy 240 points
    Hello Brian,

    Let me describe my device. I have two ADS1298R running from one external CLK. The must work synchronously to get 8 ECG channels, blood pressure channel, breathe channel and 2 respiration channels. The respiration channels runs at two different ADC`s. If i program both ADC`s by one code demodulation and modulation of respiration channels will work in the same conditions - synchronously and using the same phase. I need to shift modulation and demodulation phase of second respiration channel for 90 (for example) degrees from first respiration channel. The question is how i can achieve it. I suppose it can`t be done by programming only. I think that for that purposes i can use mode RESP_CTRL[1:0] = 0x3. I have an external FPGA (it works from the same CLK) that provides modulation clock, blocking signal and demodulation clock for each ADC separately and provide them to GPIO2, 3 and 4 inputs already shifted by the way i need it. Is it the right way of using RESP_CTRL[1:0] = 0x3?
    Now about external modulation. The internal modulator in ADS1298R generates signals RESP_MODP and RESP_MODN to generate current between two ECG electrodes. We use assymetric modulators that generates current between two separate ECG electrodes and common electrode N. So you can see we do not use RESP_MODN. I`m not sure internal ADS1298R modulator can be used in that way.

    Best regards,
    Vsevolod
  • 0 in reply to Vsevolod Anisimov
    TI__Mastermind 38745 points
    Hello Vsevolod,

    Thank you for explaining. I understand now. Yes if you generate the modulation clocks, demodulation clocks, and blocking signals externally with an FPGA, then all that should be required is to set RESP_CTRL[1:0] = 0x3 and route the signals to the corresponding GPIOs which will allow the provided respective demodulation clocks to run the respective ADS1298Rs' demodulation circuitry.

    Regards,
    Brian
  • 0 in reply to Brian Pisani
    Prodigy 240 points

    Ok Brian,

    Thanks for your explanation. Everything seems to be clear now.

    Best regards,

    Vsevolod