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ADS1298ECGFE-PDK: Query_for_Channel_1, 4 and 6 data graphs

Part Number: ADS1298ECGFE-PDK
Other Parts Discussed in Thread: ADS1298


Thank you so much for helping in previous question, problem was solved.

Now, my query is I am not getting below channel graphs as expected compared to your reference board. I am using CARDIOSIM II simulator and my registers are configured as per done in reference board.

Channel_1 : V6 - Channel1.png

Channel_4:  V2 - Channel4.png

Channel_6:  V4 - Channel6.png

I am attaching .img files for the respective channels, I am not getting why square waves are generating in my graphs. Rest all other channel's data are as per expected as you can see in the image files.

Please help me to solve my query.

Thanks and regards.

  • Hi Koustubh,

    This is typically due to clipping in the inputs, losing the reference voltage/power, or incorrect code to voltage conversion. 

    To confirm that the inputs are not clipping, try probing the inputs with an oscilloscope and confirm that the signal is within the common-mode range of the inputs by using section Analog Input of the datasheet. 

    Probe the reference and power pins as well to confirm that they are not unexpectedly dropping. 

    Please use the BIOFAQ to confirm that the code to voltage conversion is correct.

  • Hello sir,

    I checked for is there any clipping in the inputs on Oscilloscope I didn't see any clipping there, i am attaching images for reference. I also verified code to voltage conversion is correct.

    In the image file yellow line representing for correct channel results and blue line is channel with not giving correct data,

    V2: ch4_v2.jpg

    V4: ch6_v4.jpg

    V6: ch1_v6.jpg

       We are taking inputs for plotting, as after jumper points on hardware and same showing on Oscilloscope.

    is there any another possibility for such channel outputs? (i mentioned in earlier post)

    Thanks and Regards.

  • Hello,

    Also we check following reference points on ADS1298

    AVDD    +2.5V

    AVSS    -2.53V

    DVVD   +3.08V

    RESET  2.5V

    VCAP1   -1.3V

    VCAP2   0V

    VCAP3   -2.26V

    VCAP4   4.44V

    VrefP    -2.46V

    VrefN    -2.25V

    Also in above images the Yellow V4 and other are the inputs for channel that not giving accurate graphs.

    Thanks  and Regards.

  • Hi Koustubh,

    How is it that you have a negative reference voltage? (VREFP - VREFN) = -0.21V? 

    Was this measured with respect to ground or AVSS? 

    Are you using internal or external reference? Can you post a schematic? 

    If all of the register settings are the same compared to the reference board, and the reference board is working properly, more than likely there is something on your new board that is causing these errors. I would check the power, reference, and grounds of the board. The waveforms you have showed me seem to have quite a bit of noise on them which could be caused by an external source on the board. This may disrupt or shift the ground level of the board which would lead to issues. 

  • Hello,

    So 1st is we taken all reading with respect to GND.

    Also today we take our system completely on battery. but graphs are same.also i have upload my schematic of ADS1298AnalogEcgIP-AnalogEcgIP.pdfAnalogECG-AnalogECG.pdf

    The following are the reference voltages with respect to GND.

    AVDD 2.5V

    AVSS -2.5V

    DVDD  3.04V

    RESET 3.33V

    VCAP1  -1.31

    VCAP2  0V

    VCAP3  -1.31V

    VCAP4  4.41V

    VrefP    -90.1mV

    VrefN   -2.53V

    I am using external reference as you can see in my schematic.

    as you see In this schematic i have not connected VCAP1 and VCAP3 that i found during board bring up so currently i am connecting it using fly-wire on my PCB.

    I have design 4 layer PCB for ADC with Analog and Digital ground and connect them at one point using a ferrite bead.(3.3uH 470 OHM).

  • Hi Koustubh,

    Your RESET pin is nearly violating the absolute maximum specifications of the device by being 300mV greater than DVDD. All digital signals should be the same magnitude as DVDD. It is possible that this has damaged the device. 

    Your VCAP3 voltage is -1.31V when it should be 3.9V, this also points to the device being damaged.

    You have connected VCAP1 and VCAP3? Why? There should only be capacitors attached to these pins. Looking at the schematic, I see that AVSS is tied directly to VCAP3. This is incorrect and most likely the device is damaged.

    Please see the schematic in the EVM's user guide for reference:

  • Hello sir,

    Today i worked on RESET pin, and issue of RESET pin is solved now.. by updating the DVDD from 3V to 3.3V.

    My config3 register setting is 0xDC now, earlier i am doing wrong. Now i am getting VREFP as 2.4V wrt AVSS.

    The following are the reference voltages with respect to GND.

    AVDD:   2.5V

    AVSS:   -2.5V

    DVDD:   3.3V

    RESET:  3.267V

    These Voltages are wrt AVSS

    VCAP1:   1.198V

    VCAP2:  0V

    VCAP3:  6.23V

    VCAP4:  0V

    VREFP :  2.4V

    VREFN:   0V

    Still I am getting Square waves for Channel 1, 4 , 6, 8 I am not getting the reason behind.

    I am connecting Capacitors external on the pin VCAP1 and VCAP3 (I am not shorting it) also i already updated VCAP3 connected to AVSS to Capacitor with respect to AVSS.(This will fix issue in my schematic on my board)

    Thanks and Regards.

  • Hi Koustubh,

    As I mentioned in my last post, more than likely, this device has been damaged. Try switching out the device for a new one. 

    VCAP3 should be AVDD + 1.9V = 4.4V. You are reading 6.23V

    VCAP4 should be (VREFP-VREFN)/2 = 1.2V, and you are reading 0V. 

  • As per your suggestion i try with another board . As per your last post the voltages you say i.e VCAP3 = 4.4V and VCAP4 = 1.2 are with respect to AVSS or GND?

    With new board. I am getting Square waves for Channel 1, 3, 4, 6 .

    I am not getting the reason behind it.

    The following are the voltages on new board.

    The following are the reference voltages with respect to GND.

    AVDD:   2.5V

    AVSS:   -2.5V

    DVDD:   3.3V

    RESET:  3.2V

    These Voltages are with respect to AVSS

    Thanks and Regards.

    VCAP1:   1.198V

    VCAP2:   2.5V

    VCAP3:  6.23V (4.3V with respect to GND)

    VCAP4:  1.2V

    VREFP :  2.3V

    VREFN:   0V    (-2.5V with respect to GND)

  • Hi Koustubh,

    Please see this post:

    The VCAP3 voltage is much too high if this board was powered up before the schematic change was made, more than likely the device is already damaged. 

    I recommend fixing the schematic and replacing the device. 

  • Hello ,

    Thank You for your replay. Currently i am updating the old schematic and design another PCB revision.Once i am complete the schematic i will share it with you for schematic review.

    Also I want to ask is there any way that i can post my schematic privately (i.e it is not open for public), so that you can review it and give me feedback and according to it i can bugs in system.

    Thanks and Regards,

  • Hi Koustubh,

    Yes of course. I'll send you an email offline.