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ADS1298 for EMG?

Christof Giers89842
Prodigy 65 points

Other Parts Discussed in Thread: ADS1298, ADS1198, ADS1298R, ADS1294

I want design a electromyographie device with 2x ADS1298, because I've 16 channels.

Exist a reference design for EMG from TI?

Exist a reference design with 2x ADS1298?

Do I need additional amplifiers?

  • 0
    TI__Guru**** 182881 points

    Hi Christof,

    Welcome to our forum!  For EMG on the ADS1298, you should not need any additional amplifier stage.  We don't have any specific reference design for two (or more) ADS1298 devices connected in daisy chain or cascade mode.  We're looking into that, but we have nothing to share with you at the moment.

    If you've not found the FAQ page for the ADS1x9x devices yet, please feel free to look over the 'Design Notes' tab and review the FAQ's we've posted about the ADS1198 and ADS1298.

  • 0 in reply to Tom Hendrick
    Prodigy 65 points

    Hi Tom,

    Thank you for the quick answer. I thought there is a possibility to cascade ADS1298 because there is a section "Multiple device configuration" page 36 in the data sheet, but the description is not sufficient enough to connect two devices. Many questions are open (I've the ADS1298R demo kit and use the shortcuts from the circuit sheet page 76 in the sbau181 User's Guide:

    What happen with the wires WCT, RLDxx? Can this wires be connected between the two devices?

    Is better to use AC or DC input signal?

    Do I need one or two ECG_RL signals?

  • 0 in reply to Christof Giers89842
    TI__Expert 3260 points

    Hi Christof,

    From the RLD side of things, Figure 63 of the 1298R Datasheet (page 68) should show how to connect them. But to answer your last question, there is one RLD signal, applied to all RLD amplifier "RLDINV" inputs.

    For WCT, this would depend on if you're concerned with single ended measurements or not. But, for strictly EMG signals it's not needed, so removing JP16 (according to the ADS1298RECGFE User's Guide), then applying the input signal directly into the jumper headers (rather than go through DB15) might be the best option.

    However, in any case where mutliple parts/boards/etc are used, you will need to use your own software, since our EVM software is not designed for daisy chain or cascade mode.

    Is it better to use AC or DC input signal for what? I'm a little confused by what you mean.

  • 0 in reply to Michael W
    Prodigy 65 points

    Hi Michael

    thank you for the answer. I'll try some tests with the evalboards first. This will take some weeks.

  • 0 in reply to Christof Giers89842
    TI__Expert 3260 points

    Awesome! Let us know how it turns out.

  • 0 in reply to Michael W
    Intellectual 835 points

    I have a question, in cascaded mode how its work drdy pin? because on page 38, drdy is connected just in one device the other one is not connected.

    Another question RESET and PWDN, for both devices have the same configuration, i mean i cant set high reset and pwnd at the same time for both devices?

    Thanks a lot.

    If you have same example, i really apreciate your help

  • 0 in reply to Oscar Baumann
    TI__Expert 3260 points

    Hello Oscar,

    1. /DRDY: This is only an output. The figure that you pointed out essentially means that the /DRDY signals are synchronized, with the use of the START signal. Meaning that, since the two DRDY signals behave exactly the same way, only one is needed.
    2. Not really certain about what you're asking here. But, when using multiple devices, odds are that you will not have many 'extra' pins for static I/O lines, so tying the /RESET and /PWDN lines high (then relying on OPCODES) would likely be the best route to take. [This family of devices allows for software control, via OPCODE commands. If the devices are connected with the same SPI line, then you may simply give the RESET/PWDN/STANDBY/etc OPCODE commands (more information about these on page 41)]. Just be sure the devices do not share the same /CS line. As long as they have separate /CS lines, then you will be able to control which device is powered down/reset and which isn't.
  • 0 in reply to Tom Hendrick
    Prodigy 10 points

    Hi Tom,

             I think it may not meet the desired gain of EMG. For ECG, the gain of 12 may be good enough, but for EMG, we need the gain from 1000~10000 V/V. Actually I tried ADS1294 before and found the output signals were too small. Adding  additional amplifiers may help but I haven't tryed it. I would appreciate if TI can provide a design for EMG.