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Distorted o/p in EXC_OUT Signal from EVAL-AD2S1210SDZ

I am trying to use EVAL-AD2S1210SDZ to read the angle of a resolver. But when I checked the o/p Excitation signal in CRO, I am not getting a sine signal . I am getting a clamped distorted signal.

I am using the op-amp AD8397 with 0.866 gain. 

Can someone please help me to understand why not getting the exact signal at output.

  • Hi,

    The issue on the excitation waveform resolved.

    I measured across resolver initially. Later got correct waveform by putting a high resistance.

    Now I want to know What is the maximum exciation voltage we can generate using this Board. We have a resolver which needs 4.25 Vrms exciation.

    I am using AD8397 ( LK14 to LK17 in position B) .Can you please let me know What is the maximum output voltage I can get using these configuration and How I can achieve it?

  • tpsamuel,

    If your resolver requires 4.25VRMS (differential) then that is about 6Vp (12Vpp).   The RDC swings between 7.2Vpp to 8.0Vpp differentially, natively which means you would need about 1.5x gain so the 15.4K option should be sufficient for your needs (LK10, LK12, LK14, LK16 = B),   As you are using the AD8397 path if you need a bit more gain you can always use OPTION A on LK10 and LK12 and R10 and R30 to increase the gain but you'll need to be mindful of the output limit with regards to headroom and footroom for the amplifier which roughly is 0.5V on either side with respect to the rail at 100 ohm load.  The issue is that you only have 2.5V of offset through that path.  You may be better off going through the AD8662 path to ensure distortion free operation.   The principle would be the same in that if you measured the peak output from each of EXC/EXCB you could calculate the correct gain and implement in the AD8662 stage.


  • Thanks Sean.

    Can you provide the details for parallel interface also. Just want to understand that also.

    Also is it possible to use EVAL Board as standalone?

    In standalone mode, frequency will be 10kHz?

  • tpsamuel,

    For the parallel interface make the following changes to what I mentioned above.

    LK9 - No change.   Leave at position A for Parallel Mode.

    LK3 - Move to Position C and drive RD with a GPIO from the Nano board

    Move all connections for DATA I/O to J3.

    J3-1 -> DB0

    J3-16 -> DB15

    All bit assignments for the databus (DB) are in ascending numerical order.

    If you run short on I/O remember that you can access position and velocity measurements through configuration mode so you could use just DB0-> DB7 to get started.


  • Hi 

    Can you elaborate on the last portion. how to use DB0 to DB7 for measuring position as in the datasheet it is mentioned as below

    0x80 D15 to D8 Read only
    0x81 D7 to D0 Read only

  • tpsamuel,

    The register map simply tells you which bits of the position/velocity register you are accessing when addressing register 0x80 or 0x81.   If 0x80 you are effectively outputing POSITION[15:8] to DB7-> DB0; likewise addressing 0x81 you get POSITION[7:0] output on DB7-> D0.


  • Okay. So we need to set A0 and A1 as high for configuration mode and read the address 0x80 and 0x81 using that. No need to use Sample signal. Right?

  • Okay. So we need to set A0 and A1 as high for configuration mode and read the address 0x80 and 0x81 using that. No need to use Sample signal. Right?

  • tpsamuel,

    No you'll need to strobe sample to pull the data from the loop output into the output register so you can access the data from the serial interface. 


  • I did everything as you mentioned.

    We are able to set the frequency at 3KHz and control the EVAL Board using Arduino. But while reading angle from the register the angle is not correct. Angle changing with resolver. But value is wrong and its not stable. 

    Can you let me know what might have gone wrong.

  • tpsamuel,

    Can you please describe in greater detail specifically how large the error is and how it changes as you rotate the resolver?  Also could you please indicate how you are measuring the reference position?

    Also if you could provide inside regarding the following that would be beneficial as well.

    1) Are you getting any FAULT indications?

    2) Can you please indicate what the input differential magnitudes are going into the RDC?

    3) Have you confirmed that the resolver is correctly wired to the inputs?

    Also for furture reference as this is a new issue it would be appreciated if you opened a new question.  This allows other users to more easily benefit from the content shared in the thread.


  • Also if you can comment on what resolution you are using that would be informative as well.

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