ADAU1701 ADC input passband @192kHz

Hello,

I am currently searching for a small DSP used to filter and measure a 80kHz bandwidth analog signal. So I need an ADC @ 192kHz.

The ADAU1701 seems to fit my application pretty much, but I can't find anywhere in the datasheet what's the passband of the input ADC when used @ 192kHz.
Is it the same as in 48kHz sampling mode ? (shown in the datasheet, 22kHz bandwidth)
Or is it as I expect a 96kHz bandwidth ?

If you have any chart about the input ADC bandwidth with sampling rate set to 192k, that would be appreciated.
Also if you have experience about sampling a signal @192k with that chip, I'm interessting in your experience.

Thank you very much

  •    Hello tdnwcs,

       Hopefully an ADI support engineer can help you with a definite ADC response curve @ 192K.  I do know, however, of two projects which successfully ran ultrasonic signals into a ADAU1701 at fs = 192K.

    • A music student taught himself enough EE to build a -1701-based sonar-assist device for a blind friend -- see Ultrasonic Transducer
    • I experimented using a -1701 to demodulate FM stereo and RDS -- see FM Stereo Demodulator

       Both these applications require input bandwidth in excess of 50 KHz.  I don't know why the data sheet only shows 48K operation.  The input ADCs on these and like parts actually sample at many times the core sample rate in order to drive a built-in oversampled, sharp-cutoff anti-aliasing filter. The 48K response graph you see in the data sheet is actually the response of this filter!  With the DSP core running at 96K or 192K, the anti-aliasing cutoff can logically increase as well -- and the -1701 evidently adjusts this filter accordingly.  The filter's group delay drops dramatically at 192K (more so than the increased sample rate alone suggests) -- another indication that a different input filter applies there.

       Best regards,

       Bob

  • OK, since no one has answered I tested it myself:

    You're flat within 1 dB at 80 KHz, and down 3 dB at 88 KHz.  Please respond whether this test is adequate for your needs.

    Best regards,

    Bob 

  • Sorry, this answer was delayed.

    The datasheet only showed the 48kHz bandwidth, it was done a long time ago so I cannot answer why they did not include others. The converters will go all the way up to Nyquist (within reason) so at 192kHz you will get close to the 96kHz bandwidth you would expect.

    Dave T