I designed a 6-bit current-mode R2R DAC in LTSpice. This is the output spectrum with a 500kHz input sinusoid to an ideal ADC (running at 10MHz clock) which feeds directly into the DAC. Vin is input to ADC, Vout is output of DAC

enter image description here

The output FFT spectrum looks like this: enter image description here

I have a few questions about this:

  1. How do I determine the SNR and SNDR of this? Usually when I use Cadence Virtuoso for this kind of stuff, it gives me that output.
  2. Secondly, does my FFT spectrum seem okay? I know there is a lot of posts about LTSpice putting junk at the end of the FFT. I have tried my best to follow all the tips given by others on how to reduce it. (plotwinsize, etc.)
  • \$\begingroup\$ See this. When you posted the question, didn't this, or other, similar ones, come in the list of suggestions? As for SNR&co, you measure, then calculate, there's no automatic tool for that. One way to do it would be to subtract a known fundamental. \$\endgroup\$ – a concerned citizen Apr 5 '20 at 8:44
  • \$\begingroup\$ @aconcernedcitizen As I mentioned, I have followed tips given by others including that post. It has reduced it and my question was does it look okay at this point? \$\endgroup\$ – AlfroJang80 Apr 5 '20 at 18:12

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.