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ADS1605: ADS1605 narrow band dynamic range

Juha Sarkki
Prodigy 10 points
Part Number: ADS1605

Tool/software:

My application is a digital radio receiver (modification to an existing legacy product). The received signal frequency is between 20kHz and 1MHz and there will be several about 50 dB stronger interfering signals at frequency offsets 5...50 kHz from the received signal.

The datasheet shows wide band input spectrum on several pictures on page 12. However, from these pictures one cannot say if the SFDR, SNR and THD are retained for these close offsets also.

So, are the dynamic range numbers stated in the datasheet true also for the close offsets?

  • 0
    TI__Mastermind 40860 points

    Hello Juha,

    Welcome to the TI E2E community.

    I believe you are asking for IMD, which occurs with two closely spaced signals at similar amplitude and is a result of the non-linearity of the ADC.  We do have one spec in the datasheet that shows these effects for signals near full scale.  As you can see below, the resulting distortion has a similar SFDR (-98dBFS).  I would not expect SNR to be significantly effected since it is limited by thermal noise, nor would I expect THD to be significantly effected based on results for similar devices at lower bandwidths.

    Unfortunately, this is the only data that we have for the ADS1605.

    Regards,
    Keith Nicholas
    Precision ADC Applications

  • 0 in reply to Keith Nicholas
    Prodigy 10 points

    Hello Keith,

    thanks for your reply.

    IMD is one of those things limiting dynamic range. That picture shows IMD on relatively narrow band which correlates well with my application.

    However, SFDR is also important. Consider just one strong blocking signal say -6 dBFS level 10 kHz from received signal. Received signal is at -56 dBFS needing 10-20 dB of SNR. No intermodulation taking place but if there are any spurs around the received signal they can limit the signal-to-noise ratio of the received signal.

    But OK, if no more data is available I guess I just need to try it.

  • 0 in reply to Juha Sarkki
    TI__Mastermind 40860 points

    Hi Juha,

    Agreed, best to test in your exact use case to know for certain.

    Regards,
    Keith