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ADS1298: Flat response for internal test signal in RDATA mode

Part Number: ADS1298

I am currently sampling the inputs with the internal square wave test signal.

However, I am only getting the square wave in RDATAC mode - not in RDATA (single shot) mode where the response is flat for every channel.

Is this normal behavior? If I change the input multiplexer from "Test signal" to "Normal Input" I can see my ECG signal I am supplying externally (in RDATAC as well as in RDATA mode) so it seems like there is a problem if MUX is set to test signal and device is in RDATA mode.

Any ideas how this could be caused?

  • Hi,

    Thanks for the post.

    The RDATAC and RDATA mode for reading data from the ADC should not be affected by the MUX setting for the input channels. Is your data rate for the RDATA mode the same as RDATAC mode? You may want to try changing the test signal frequency and amplitude for verification. Are you able to get the correct voltage level for the test signal in RDATA mode even if the response is flat?

    Thanks

    -TC

  • No, data rate is the same for both modes (HR-Mode with 1kSPS). This is one exemplary response:

    11418;12306;16339;24804;14654;25113;18829;24945

    I don't know exactly how to convert these numbers into voltages but it is pretty close to 0V (I guess), and they basically stay the same:

    11744;12309;16319;25138;14979;25434;19178;2530

    In RDATAC mode, I get these values (exact same settings as in RDATA mode):

    -29264;-29464;-25505;-15897;3;-117061;-117797;-101861

    and

    12558;12288;16319;25871;0;50324;49080;65144

  • Hi,

    Please see the FAQ link below for the methodology to convert the ADC output codes to volts. Can you check the RDATA mode with external square wave test signals to ensure there is no issue with the signal chain? Please provide the complete registers setting and also some screenshots of the RDATA SPI interface.

    Thanks

    -TC