The ADC12DJ2700 will be used to configure the system using undersampling technique.
I am trying to use the DDC module in ADC12DJ2700, and while reading the datasheet regarding the NCO frequency setting, I had a question in the Rational NCO frequency setting mode.
In the Datasheet, fs = 2457.6MHz and fnco = 5.02MHz as examples. (I think fs = fdevclk.)
Basic NCO frequency setting mode is as follows :
Substituting the above formula, FreqAx is 873085.867. If you cut the decimal point, FreqAx = 873085, and fnco is 5.0199995MHz. (not same as 5.02MHz)
According to the description of the datasheet, I need to use rational NCO frequency setting mode to set the exact NCO frequency I want.
However, as I looked at the formula, I don't understand why the rational NCO frequency setting mode is separate.
The method of obtaining freqAx value in rational NCO frequency setting mode is as follows.
(typical value of fstep is 10KHz)
In my understanding, the only difference between how to obtain FreqAx values in basic mode and rational mode is that truncation of the fractional part of the calculated result in basic mode and rounding in fractional mode.
Is what I understand correct?
Looking at the formula attached above, I don't understand why the NCO_RDIV value is calculated.
