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ADS1298ECGFE-PDK : External Test signal via Signal Generator

Komal Mariam
Prodigy 130 points
Other Parts Discussed in Thread: ADS1298ECGFE-PDK, ADS1298

Hi,

I am carrying out preliminary testing on the ADS1298ECGFE-PDK and it's software. I successfully tested the kit with internal test signals and now I wish to provide an external sinusoidal signal via signal generator in order to see it behave as an ADC.

I have read the user guide but  do not fully understand how to connect the function generator to the ADS.

Is it possible to view the signal on a channel if I connect it via DB15 connector or should I remove the jumpers and connect the generator to the VINP and VINN pins?

Thank you in advance,

Komal

  • 0
    TI__Mastermind 38745 points
    Hi Komal,

    Either way should work. The DB15 connector is useful if you have a patient simulator that uses electrode cables to connect, but if you were to remove the jumpers and connect a function generator to the ADC side of the generic connectors labeled JP26 - JP33 on the schematic, that should work fine as well.

    Regards,
    Brian Pisani
  • 0 in reply to Brian Pisani
    Prodigy 130 points

    Thank you for answering Brian.

    I am connecting the function generator to the ADC side on the pins marked with + and - for CH8. But the software's Scope tab does not display the signal that I have input. I am attaching the screenshots for the control register settings that I have set . 

    The input signal is a 13 Hz- 1V sine wave. However this is what the scope is showing.

    I have taken a zoomed screenshot to see the output obtained clearly.

    Please tell me what needs to be changed here to view the input signal.

    Thank you in advance.

  • 0 in reply to Komal Mariam
    TI__Mastermind 38745 points
    Hey Komal,

    Looking at your signal, that fast frequency waveform seems to have a period of around 10 samples which is roughly 500 SPS/10 S = 50 Hz which is probably the utility frequency. That frequency is being coupled to your inputs from your signal source. To see whether or not your actual signal is making it to the ADC, check the FFT tab and see if you can identify your signal in its respective frequency bin.

    As a side note, you're going to need to set your common mode to a valid range somehow since it looks like your signal generator is at an offset with respect the the board. One way to do that with your current setup would be to hook the ground wire of you signal gen to the board AVSS which corresponds to -2.5V. Then you could give the signal you generate an offset of 2.5 V to put its common mode at 0 V with respect to the ADS1298. The signal wire can connect to the positive input of the channel and the negative input can be wired to the RLD output. Make sure the RLD amp is configured as just a mid-supply buffer rather than using channel inputs to determine its outputs. That way when the ADC measures the differential voltage on the channel, it measures your input signal with respect to the mid-supply voltage which is zero volts. This method may seem roundabout, but setting the common mode for biopotential measurements is a challenge in the first place and so the EVM was designed to showcase this device's ability to do that using the RLD amplifier. If you have a simpler way of setting the common mode for your purposes, then by all means you can do that instead.

    Regards,
    Brian Pisani
  • 0 in reply to Brian Pisani
    Prodigy 130 points

    Hello again Brian,
    I have connected the function generator to channel 2, JP32 between Pins 2 and Pins 4. I have given a sinusoidal signal of 13Hz. This is the resultant waveform I am getting. It seems the offset problem has disappeared. 

    And here is it's FFT. I cannot see any frequency at 13Hz. Does it mean my signal is not reaching the ADS? 

  • 0 in reply to Komal Mariam
    TI__Mastermind 38745 points
    Hey Kormal,

    Looking at your first image, the period of that waveform looks to be around 40 samples which at 500 SPS corresponds to a frequency close to 13 Hz so I think your signal is getting to the converter! Also, to get a better picture of your spectrum, you should try to change the display so 0 dB is at the top of the graph.

    Brian Pisani
  • 0 in reply to Brian Pisani
    Prodigy 130 points

    Thank you so much for your help, Brian.

    I was finally able to view the signal via the ADS1298.

    Here's what I did:
    Connected the signal generator to Pin 2 of one of the channels and the GND of JP5. Then connected RLDOUT to PIN 4 of the same channel. 

    Regards,