[time-nuts] fast freq. synthesis schemes

[Lux, Jim (337C)]

On 10/15/09 5:56 AM, "Luis Cupido" <cupido at mail.ua.pt> wrote:

> Hi Bert,
> 
> Thanks for the input.
> 
> briefly;
> -Phase noise is not too important
> -It is to make just a few (and cost is not a major issue)
> 
> The suggestions using prescalers or any other high speed
> digital chips may bring simplicity while compared with
> the design using multiple loops and harmonic mixers and samplers
> that is something I had in mind when I place the question out.
> I was wondering if recent technology would make possible
> to have a simpler approach.
> 
> I like your first suggestion but I fear the spurious...
> I have no clue how bad it will be, but I guess I can only
> be sure if I make a prototype of that.
> The second one I must check how small would be the step...
> 1 MHz would be enough for a start.

The spurs might not be as bad as you think... The newer crop of DDS include
some forms of error cancellation for close in spur reduction, so the "in the
loop bandwidth" part is cleaner.  Also, maybe you can use clever choice of
DDS clock rate to make sure that you only need "nice" phase increments that
evenly divide into the lookup table length.