Frequency above 20 kHz with Sigma Studio and AD1940?

Hello, i want to expirement with sound in the ultrasonic frequency range, deom about 15 kHz to 40 kHz.

Can Sigma Studio operate in this frequency range, and can i do filtering, ect in this frequency range.
I want to use the AD1940 on the evaluation board EVAL-AD1940MINIBZ-ND , can i use this for my tests?
Also, i am concerned about anti alizing filters on the evaluation board will cut off too low, is that a concern, and can i modify these filters if they are there?

If the above cannot be done, do you have any suggestions for evaluation solutions in this frequency range.

Thank you if you can help me

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  •      Hello,

         The AD1940 can handle 40 KHz signals at (for example) a 96 KHz sample rate, but unfortunately the ADAU1940MINIBZ evaluation board cannot.  Since the AD1940 had no internal converters, it relies on the eval board's AD1938 codec -- which has been hardwired for 48 KHz operation.  Thus, although you can set the AD1940 to run at 96 KHz from SigmaStudio, the codec won't go along for the ride -- and you'll get frequency fold-over around 24 KHz.  I just tried running this board at 96K and it definitely doesn't work as expected.  The AD1452MINIZ eval board shares this same limitation.

         Check out the ADAU1701MINIZ board -- the ADAU1701 has internal converters so they operate according to the sample rate you set in SigmaStudio.  See this post for how to specify sample rate:

    How do I change the sample rate of my SigmaStudio system? 

    Note that you don't have to change any hardware (crystal, etc). to go from 48 to 96 to 192K on the -1701 eval board.

         The 1701's two on-chip ADCs have integrated digital anti-aliasing filters -- so there's no analog filter at the chip input, and nothing you need to adjust or worry about.  Its four DACs feature oversampling reconstruction filters, so the board only uses a simple 50 KHz RC output filter.  It rolls off slightly at 40 KHz (see traces below) -- if this is a problem, you could reduce the value of the board's output filter caps, C13 and C14.

    SigmaStudio test project:

    Output at 20 KHz and 40 KHz:

         

         Best regards,

         Bob

Reply
  •      Hello,

         The AD1940 can handle 40 KHz signals at (for example) a 96 KHz sample rate, but unfortunately the ADAU1940MINIBZ evaluation board cannot.  Since the AD1940 had no internal converters, it relies on the eval board's AD1938 codec -- which has been hardwired for 48 KHz operation.  Thus, although you can set the AD1940 to run at 96 KHz from SigmaStudio, the codec won't go along for the ride -- and you'll get frequency fold-over around 24 KHz.  I just tried running this board at 96K and it definitely doesn't work as expected.  The AD1452MINIZ eval board shares this same limitation.

         Check out the ADAU1701MINIZ board -- the ADAU1701 has internal converters so they operate according to the sample rate you set in SigmaStudio.  See this post for how to specify sample rate:

    How do I change the sample rate of my SigmaStudio system? 

    Note that you don't have to change any hardware (crystal, etc). to go from 48 to 96 to 192K on the -1701 eval board.

         The 1701's two on-chip ADCs have integrated digital anti-aliasing filters -- so there's no analog filter at the chip input, and nothing you need to adjust or worry about.  Its four DACs feature oversampling reconstruction filters, so the board only uses a simple 50 KHz RC output filter.  It rolls off slightly at 40 KHz (see traces below) -- if this is a problem, you could reduce the value of the board's output filter caps, C13 and C14.

    SigmaStudio test project:

    Output at 20 KHz and 40 KHz:

         

         Best regards,

         Bob

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