host VI configuration

[afd-2000]

I was just wandering about the frequency controls in the Host VI for the blocks labeled "DAC Config IQ" and "ADC NCO."  I've generated a sine wave in the DAC timed loop in my FPGA VI and am having trouble viewing this sine wave in the host VI.  I'm not too sure what values these frequencies should be set to.  I know the frequency for the ADC NCO block controls the NCO frequency that translates the signal, though I'm not too sure how to set the IQ tuning word frequency.  Can anyone help me out here?

[JerryAL]

Hi

I’m not sure what you are referring to in terms of the IQ tuning word frequency.  Are you referring to a control on a NI 5640R VI? 

Just based on tuning word, I think of DDS blocks to create frequencies in the baseband as the NI 5640R is concerned.  Depending on how you are applying the data to the DAC, it may show up as a simple frequency shift from the configured DAC’s NCO frequency, or even as a simple AM waveform on the output of the DAC if you only vary the I data and leave the Q constant or zero.

A DDS tuning word is usually just a mathematical number that determines how far a counter/accumulator counts for one clock cycle.  In DDS, the accumulator represents one cycle of a waveform.  The rate that the accumulator rolls over represents the frequency of the waveform.  If the tuning word is a value that will cause the accumulator to roll over every X (5 for example) clock cycles, the frequency of the waveform will be the clock rate divided by X (5).  If the clock rate is 10 MHz, the frequency will be 2 MHz if it takes 5 clock cycles for the accumulator to roll over.

Jerry