[time-nuts] fast freq. synthesis schemes

Luis Cupido cupido at mail.ua.pt
Thu Oct 15 12:56:09 UTC 2009


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.


Thanks
Luis Cupido.


EWKehren at aol.com wrote:
> Luis
> There is not really enough information to make a good recommendation. Is  
> this a one off or is the plan to make multiple units, what are the phase 
> noise  requirements, what are the cost limitations? If cost is a major issue 
> there are  in my opinion only two options.
>  In both cases a VCO has to be used presetting with a fast  D/A.  In the 
> first case you pre scale by 16 and feed an AD 9910 DDS as a  programmable 
> divider using a 100 MHz output in to a Hittite HNC 439 phase  comparator with 
> all the shortcomings of a DDS multiplied by the total divider  ratio. 
> The second option is a Hittite HMC 700 fractional PLL and use 50 or 60 MHZ  
> compare frequency. You have to pre scale by 2 . Having used the all the 
> above  components I can tell you the DDS works reliable at 1200 MHz in and the 
> 700  works great at 9 GHz.
>  I have not gone for switching speed but in my case emphasis is on  phase 
> noise and resolution. As a matter of fact a friend of mine and I are doing  a 
> low cost signal generator from 100KHz to 26 GHz in one Hz resolution using 
> the  Hittite 700 part. Phase noise goal at 8 GHz is -100 dbc, 10 KHz offset. 
> We use  surplus yigs.
> Bert Kehren WB5MZJ
>  
>  
> In a message dated 10/14/2009 3:25:33 P.M. Eastern Daylight Time,  
> cupido at mail.ua.pt writes:
> 
> Hi,
> 
> I'm looking for the schemes used on the
> frequency  synthesizers that change frequency
> in few microseconds time (or less)
> at  microwaves lets say circa 12-18Ghz)
> Obviously with some resolution (let's  say 100Khz step
> or in that order)(otherwise it would
> be a trivial  exercise in the BW of the PLL loop filter)
> 
> Does anyone know of some  paper or tech notes from
> some instrument or modules that show block  diagrams
> of such?
> 
> I have many info on mw synthesizers but all fall  into
> microwave radio style of things with much higher
> resolution (khz  and less) and much longer
> switching times (millisencods or more).
> Info  on fast stuff I can't really find.
> 
> 
> I'm thinking of experimenting on  something along those
> lines so... all comments are  welcome.
> 
> Thanks.
> 
> Luis  Cupido.
> ct1dmk.
> 
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