Hi all,

I have an ADF4350 setup to generate 3177.216MHz and 1588.608MHz derived from a 26MHz reference clock and would like to work out the frequency error down to a fraction of a Hz. Assume we have a perfect 26MHz reference clock.

Using the following settings:

input ref clock - 26MHz

pfd freq = 2.6MHz

Prescaler: 8/9

N counter: 1222

frac: 4

Modulus: 650

R counter: 10

doubler : 0

BS counter: 21

RF divider: 2

Given these settings how can I calculate back the actual frequency of the VCO output? The frac-n synth has only a finite resolution so the VCO will not be exactly 3177.216MHz. 12bits for the fractional and 12bit modulus. If I plug this in the formula from the datasheet I will get back exactly the frequency I want. The formula though uses floating point numbers though so you won't see the rounding errors.

target RF output freq: 1588608000.000 Hz

Aux output freq: 3177216000.000 Hz

calculated Rf freq: 1588608000.000 Hz

Many thanks

The ADF4350 evaluation board control software will do these calculations for you.

I put together these settings for your application. I've used a 26 MHz PFD frequency to minimize your phase noise while still achieving your required frequencies:

If you try to set the output to a frequency that cannot be achieved, the software will highlight it in red:

Free download of the software here: http://ez.analog.com/message/38857#38857