[time-nuts] 10MHz to 80MHz frequency multiplier suggestions

[Bob Camp]

Hi

Another way to filp that around is that the same ADC's begin to degrade if the broadband phase noise isn't at least in the 150's. With an 18 db penalty for multiplying, that puts you into the 170's for phase noise out of the TBolt. Even if the TBolt OCXO is that good (doubtful) building a multiplier chain with that sort of floor is a *very* difficult thing to do.

Bob


On Feb 1, 2011, at 5:19 AM, John Miles wrote:

> 
>> 
>> Before one can conclude such a solution is adequate one needs to know
>> the ADC requirements for clock jitter.
>> If the ADC is a high resolution pipelined ADC like those available from
>> AD and LTC then such a solution will degrade the performance
>> significantly.
>> These ADCs require clock cycle to cycle jitter of a few tens of femtosec
>> or less to realise the datasheet performance.
> 
> Actually it's better (worse?) than that, for two reasons: 1) none of those
> ADCs can take advantage of a clock noise floor much better than -150 dBc/Hz,
> and 2) the clock noise is improved by 20*log(clock/input).  That means an HF
> receiver like the Perseus will be able to shrug off some or all of the noise
> added by the multiplier, depending on where you tune it.
> 
>> The intrinsic jitter of an ACMOS gate is too high by a factor of
>> 20 or more.
> 
> For an HF source, -133 dBc/Hz is a very small amount of phase noise at 1 Hz.
> For comparison, both the HP 10811 and later-model Thunderbolt OCXOs are in
> the -100 to -110 dBc/Hz neighborhood at 1 Hz.
> 
> The residual PN of a 74AC04 is about -135 dBc/Hz at 1 Hz, measured on a 10
> MHz carrier(1).  The TSC 5115A, whose ADCs are from the same basic family as
> the one in the Perseus, has a (non-correlated) 1-Hz measurement floor
> of -133 dBc/Hz(2).
> 
> Bottom line: if you use reasonable construction practices and maintain a
> high signal level throughout the chain, I don't think there is much to worry
> about when driving an ADC with a 10 MHz->80 MHz multiplier.  I would worry
> more about spurs than noise.
> 
> (1) http://www.ke5fx.com/ac.htm
> (2) http://www.symmetricom.com/link.cfm?lid=6156
> 
> -- john, KE5FX
> 
> 
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