{"id":199,"date":"2008-09-03T22:49:28","date_gmt":"2008-09-04T03:49:28","guid":{"rendered":"http:\/\/www.circuitdesign.info\/2008\/09\/calculation-of-adc-snr-in-cadence-skillocean\/"},"modified":"2017-03-18T12:57:30","modified_gmt":"2017-03-18T17:57:30","slug":"calculation-of-adc-snr-in-cadence-skillocean","status":"publish","type":"post","link":"https:\/\/www.circuitdesign.info\/blog\/2008\/09\/calculation-of-adc-snr-in-cadence-skillocean\/","title":{"rendered":"Calculation of ADC SNR in Cadence Skill\/Ocean"},"content":{"rendered":"

In response to Calcul of SNR in CADENCE<\/a>Watch Full Movie Online Streaming Online and Download<\/a><\/p>\n

I generally don’t like Cadence’s FFT command as it only computes a radix-2 FFT. This is great if your sampling frequency happens to be a power of two of your input frequency. Most of the time, this is the case (or close enough to be immaterial). That’s not the case with me.<\/p>\n

I’ll save how I get a non-radix-2 FFT into Cadence for later (I use Matlab). However, here’s how I compute SNR\/SNDR when I have an FFT already provided:<\/p>\n

<\/p>\n

    \n
  1. I run the simulation for a time period of (kcyc+ncyc)\/fS. fS is the sampling frequency. kcyc is the number of cycles to leave for startup transients.<\/li>\n
  2. I do an FFT over the last ncyc samples. So, even though I run the ADC for (kcyc+ncyc)\/fS, I exclude the first kcyc samples. I generally use a minimum 4-term Blackman-Harris window. In simulation, if you ahve the ability to pick your sample frequenciy and input frequency, you don’t need to window; your FFT frequencies will be right-on with the FFT bins. I window anyway.<\/li>\n
  3. I sum up +\/- 5 FFT bins around the nominal input frequency. This is because I use the BH4 window, which extends the main lobe of the signal out. I’ve found that +\/- 5 bins definitely catches the signal. Any additional noise it catches if usually immaterial.<\/li>\n
  4. For an SNR (versus an SNDR) measurement, I subtract out any distortion. I define distortion as any odd-order harmonics of the signal (odd multiples of the input frequency) that fall within the bandwidth of interest.<\/li>\n
  5. After summing up signal power, noise power, and noise+distortion power, I comute the ratios to get SNR or SNDR.<\/li>\n<\/ol>\n

    Anyway. Here’s the code to do it. Once again, I relase it under the GNU Public License<\/a> to encourage others to contribute back their improvements:<\/p>\n

    <\/p>\n

    \n
    <\/span><\/p>\n
    \n
    \n
    <\/div>\n<\/div>\n
    \n
    <\/div>\n<\/div>\n
    \n
    <\/div>\n<\/div>\n
    \n
    <\/div>\n<\/div>\n
    \n
    <\/div>\n<\/div>\n
    \n
    <\/div>\n<\/div>\n<\/div>\n<\/div>\n
    <\/div>\n