[time-nuts] fast freq. synthesis schemes
lists at cq.nu
Thu Oct 15 17:05:15 UTC 2009
The loop bandwidth needs to be quite wide while you are switching. Once you
are done with the "move" you can shrink the bandwidth quite a bit.
Depending on what you are trying to do, that may or may not help ...
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Luis Cupido
Sent: Thursday, October 15, 2009 10:21 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] fast freq. synthesis schemes
My fear is "in the loop bandwidth" is a lot of BW
as I need a wide loop for it to be fast.
Okay, it sounds a nice path to investigate.
Lux, Jim (337C) wrote:
> On 10/15/09 5:56 AM, "Luis Cupido" <cupido at mail.ua.pt> wrote:
>> Hi Bert,
>> Thanks for the input.
>> -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
> some forms of error cancellation for close in spur reduction, so the "in
> 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
> evenly divide into the lookup table length.
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