Hello Labmaster,
You proposed that you needed to
generate every frequency with no more than 2 periods. To do this, you
need to ensure that Sampling rate / desired frequency = some value x.
"x" has to have either no remainder or a remainder of 0.5. With a
remainder of 0.5, you can generate the frequency with only 2 periods
and still meet phase coherency requirements. With a remainder of 0,
you can simply generate the desired frequency with a single period.
For
example, lets say you want to generate a frequency of 1.2MHz and
1.3MHz. The sampling rate can be anything you want within the limits
of the board. We could first look for a common sampling rate that
would equate to an single period generation. For example,you could
multiply 1.2 by 1.3 and come to a common sampling rate of 15.6MHz.
This will give either 12 or 13 as the number of samples. Now, we need
to make sure this is a multiple of 4. To do so, you can simply
multiply these numbers by 4 to give a new number of samples. For a
single period, we need to force this to a new update rate. So, for
15.6MHz / 1.2MHz = 13 * 4 = 52*1.2MHz = 62.4MHz. For the other desired
frequency, it will be 15.6MHz / 1.3MHz = 12*4 = 48*1.3MHz = 62.4MHz.
Unfortunately,
you will need to work with these numbers/equations to find a way to
optimize this solution, but this should get you started. I only mentioned the 0.5 solution as an additional way to optimize your results.
Regards,
Paul C.
Message Edited by Paul C. on 05-22-2009 01:20 PM
