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spectrum function in OCEAN

ksnf3000

Hi All,

I am trying to calculate the Effective no.of bits,SINAD,SNR etc. for a delta-sigma ADC. As per the OCEAN reference document on page 427  for the function "spectrum" , it shows that these parameters are calculated using the DFT of any given input signal. 

However,when I am using the below expression its showing that evaluation of the expression has failed. 

spectrum (dft(VT("/net028") 0 1e-06 4096 "Rectangular" 1 "default") 4096 500K 1 2G "Rectangular" nil "sinad")

Please provide your insights on this and what could be the possible solution for this.

FYI: I calculated the DFT separately and used the spectrum function which gave me an erroneous result( I assume!!) 

Regards,

Kashif 

  • ksnf3000

     Hi All,

    While calculating the SNR,ENOB using the "spectrum" function in calculator,I seem to be getting rather erroneous results. As seen in the attachment, I am getting "-1.9 bits" as my resolution and the SNR/SFDR is 0!!  I really don't understand this why.

    I have followed the below steps for the above results

    Sent the transient output data to calculator. This is my input signal to the spectrum function.

    32768 is the number of bins I desire to use

    800K is the bin size. My transient simulation time was 1.25u

    1 is the starting FFT frquency

    13.1072G is the end FFT frequency.  // I had also performed a dft of the same signal from which I obtained the input & output signal       frequencies.

    Please let me know what is the problem. Is this an issue with Cadence or in the manner in which the computation is being done?

    Thanks!

    Kashif

     

  • Andrew Beckett

    Kashif,

    It's hard to debug without seeing the input data. Please contact customer support.

    Kind Regards,

    Andrew.

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