In our application, the flowing is DAC38RF89's configuration. When we output 1GHz signal, there is no spurs. But other frequencies, it can see spurs.
We found that it was caused by the inverse sinc filter. If disable the inverse sinc filter, there is no spurs.
The frequency of spurs is related to the signal frequency. For example, the spurs cannot be seen at 1GHz, but the output power has a few dB change; at 999.999MHz, the spurs will be at 999.989MHz and 1000.009MHz; at 999.998MHz, the spurs will appear At 999.978MHz and 1000.018MHz; that is, the spurious frequency is Fout±(1G-Fout)*10. When the inverse sinc filter is turned off, the spurs disappear.
However, if the signal is output through the NCO, whether or not the inverse sinc filter is enabled, there is no spurious.
Why does theinverse sinc filter cause this problem？spurs.rar
