• State Resolved
  • Locked Locked
  • Replies 7 replies
  • Subscribers 46 subscribers
  • Views 1307 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADS8881EVMV2-PDK: ADC pro and PSI output frequency problem

Marc Liu
Intellectual 2860 points
Part Number: ADS8881EVMV2-PDK
Other Parts Discussed in Thread: ADS8881, ADCPRO,

Hi,I meet some problems while test the ADS8881 EVM in lab

I used two test board:

  • PSI(Precision signal injector) + ADS8881 EVM + ADC pro
  • PSI(Precision signal injector) + ADS8881 EVM2 + EVM GUI

The problems are as follows:

  • PSI(Precision signal injector) + ADS8881 EVM + ADC pro
    • How to set the FFT? I find Fundamental Leakage Bins, harmonic leakage bins influence SNR and THD a lot
    • The SFDR in the attachment “1-ADC pro > SFDR” seems not correct
  •  PSI(Precision signal injector)
    • Does the PSI just use for output 2kHz? While output 1kHz or 3kHz, the SNR result is very bad(52.9dB@1kHz,  72.9dB@3kHz)

Now I have AP525, but I didn’t have differential BNC to SMA cable. So do I can just use PSI@2kHz to do the test? How if I want to adjust the input signal frequency?

Looking forward to your reply. Thank you.

Marc

How to set the following parameters?

Harmonic leakage bin=0, THD=-112.8dB

Harmonic leakage bin = 3, THD=-103.31 dB

  • 0
    TI__Mastermind 49445 points

    Hello Marc,

    We are looking into this; we will get back to you shortly.

    Thank you and Best Regards,

    Luis

  • 0 in reply to Luis Chioye
    TI__Mastermind 49445 points

    Hi Marc,

    The ADS8881EVv2-PDK is the new evaluation kit developed on the compact PHI board controller. It replaces the legacy ADS8881EVM-PDK based on the MMB0 platform and ADCPro.

    In the case of the new ADS8881EVMv2-PDK, the FFT spectrum analysis tool uses by default the 7-Term Blackman-Harris window and the software automatically applies the appropriate leakage bins; providing also an accurate measurement of SFDR.

    As you have mentioned, when using the legacy ADS8881EVM-PDK ADCPro, the leakage bins must be set manually. On ADCPro please select the 7 term B-Harris window and the window leakage pins should be set as 7 DC leakage bins and ±7 fundamental bins and ±7 harmonic leakage bins.  More details about FFT windows can be found at:

    http://electronicdesign.com/analog/choose-right-fft-window-function-when-evaluating-precision-adcs

    In order to obtain the expected FFT performance of the ADS8881, a very pure sinusoidal signal must be applied. The PSI (Precision Signal Source) provides a very pure, low distortion, low noise signal at 2KHz. It accomplishes this signal purity by using an audio DAC cascaded with an 8th-order Bandpass filter tuned at 2KHz.

    On the PSI (Precision Signal Injector), it is possible to override the 2-KHz Bandpass filter, and test other frequencies; however, since the 2kHz Bandpass filter is not present, the quality of the signal is degraded; and as a result the ADS8881 will not reflect the expected FFT performance. If you require test AC performance at other frequencies; I recommend using a fully-differential, high performance signal generator. In the case of the Audio Precision, the best performance is obtained by connecting the balanced output of the AP to the SMA inputs of the EVM with properly shielded cables.

    If you wish to override the Bandpass filter in the PSI board, JP1 and JP3 jumpers need to be moved from the FLT position to the BP position. The image below was taken from the ADS8900 user guide showing the PSI jumpers. Please note, performance will be degraded in comparison to the 2khz filtered signal.

    Many Thanks,

    Kind Regards,

    Luis Chioye

    SAR ADC Applications

  • 0 in reply to Luis Chioye
    TI__Intellectual 2860 points

    Hi Luis,

    Thanks so much for your detailed reply.

    I select the 7 term B-Harris with 7 DC leakage bins and ±7 fundamental bins and ±7 harmonic leakage bins.

    The result under PSI@2kHz is as follows, SNR is 110dB, even higher than the datasheet, may not accuracy enough.

    It seems ADS8881 EMV2 + EVM GUI is better than ADS8881 EMV + ADC pro.  So I'd like use the former one to do the following test.

    How about your opinion?

    Thanks again.

    Marc

  • 0 in reply to Luis Chioye
    TI__Intellectual 2860 points
    Hi Luis,

    I'd like to ask one more question, if I want to test the DC performance and do the calibration of gain and offset of ADS8881 EVM2, I need a accurate source. Do you have any recommended instruments?

    Now I have AP525 and PSI and a SourceMeter with 100nV accuracy. All seems not match the LSB requirement.

    So could you give some suggestions?

    Many thanks.

    Marc
  • 0 in reply to Marc Liu
    TI__Mastermind 49445 points
    Hi Marc,

    Yes, please use the ADS8881EVMv2-PDK for your AC tests as this GUI provide accurate FFT results and the legacy ADS8881EVM-PDK is now obsolete. A stable, high precision, low drift DC source such as the Data Precision 8200 calibrator could be used in combination with a high resolution meter (Agilent 3458 or equivalent) to measure accurately the voltage at the inputs of the ADC to perform the Gain error measurements. You must also ensure to account for the initial accuracy of the reference in your measurement.

    When using the balanced output of the AP, the ADS8881EVM will meet performance. The best performance is obtained by connecting the balanced output of the AP to the SMA inputs of the EVM with properly shielded cables. Ensure to use a fully-differential signal close to full-scale (-0.5dB) for your tests. Alternatively, you could use the PSI board.

    Best Regards,
    Luis
  • 0 in reply to Luis Chioye
    TI__Intellectual 2860 points
    Hi Luis,

    Thanks for your detailed reply and suggestions. I will use ADS8881EVMv2 and PSI to do the following test.

    Best regards,

    Marc
  • 0 in reply to Marc Liu
    TI__Mastermind 49445 points

    Hi Marc,

    Please see below, I have previously tested a new ADS8881EVMV2 using the AP SYS-2722, connected with the XLR balanced output to the SMA inputs on the ADS8881EVMv2 through the shielded cables.  Please see pictures of the set up and FFT results below meeting SNR=99.1dB and THD=-121.5dB.

    I used Fin=1kHz to make a distinction from the PSI board (2kHz).

    Thank you and Best Regards,

    Luis Chioye

    SAR ADC Applications