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TMDSDOCK28379D: Low SINAD

Danilo A.
Mastermind 27330 points
Part Number: TMDSDOCK28379D

Hi Team,

We received this inquiry from our customer.

So my problem is that we recently bought the kit TMDSDOCK28379D

We are testing it and we're getting a SINAD lower than indicated in the Microcontroller data sheet when using one of the ADC of the microcontroller.

We would like to know if we're doing something wrong in our test. We would like to know if it is possible to discuss our test setting with someone who can confirm if under this setting we should get the SINAD indicated in the data sheet.

We're getting 60 dB. I wanted to mention the following:
- The signal generator is a NI DAQ USB-6363. We measured its SINAD and we're getting approx. 80 dB.
- Signal Frequency: 1 kHz
- Signal Amplitude 1.6 V.
- Sampling rate of the ADC = 20 K.

Also, In the User Guide of the control card, they recommend for this test to "place additional female SMA connectors on the control card docking station", however, we don't see the appropriate holes to place such SMA connectors in the docking station. We wonder if there is another docking station that we are not aware of.

Regards,

Danilo

  • 0
    TI__Guru* 76730 points

    Danilo,

    I would suggest the customer take a look at this application note, it will help them understand the driver circuit/settings they can use to optimize the ADC performance https://www.ti.com/lit/spract6.  Especially if they are evaluating 16-bit mode, understanding the circuit model/drive will be key to seeing the numbers we publish in the DS.

    I'm not exactly sure what is meant by the NI USB-6363 comment, from what I can see this device has a 16-bit ADC so perhaps the customer is stating they are measuring their function generator with the 6363 and it is 13-bit accurate?((80-1.76)/6.02)  Perhaps there is a DAC on that device that I didn't see the specification for.

    In terms of amplitude, in order to get the best separation between signal and ground they would want to use the full scale range of the ADC, which on the controlCARD is connected to a 3.0V reference. 

    The reference to the SMA connector, I think is for the LaunchPad, but the key is really to evaluate the app note and make sure the driver circuit/sampling window of the ADC are aligned to adequately charge the internal S/H cap.  The SMA connection(or any co-ax connector) typically give a more robust/noise free connection needed when working in these bit ranges.

    In terms of a known good source, we recommend using this one from TI https://www.ti.com/tool/PSIEVM it provides both single ended and differential outputs which mates up well with this ADC.  I believe TI designed this EVM to help customers evaluate the goodness of our ADCs, either discrete or embedded.  Custpmer can look at the references and support circuit/filters on this design as well.

    Best,

    Matthew