[time-nuts] 74HCT9046A Max. Operating Frequency

Bob Camp lists at rtty.us
Tue Apr 29 07:06:32 EDT 2014


Hi

It’s close in noise in the case of the HCT series parts.

Bob

On Apr 29, 2014, at 3:13 AM, Magnus Danielson <magnus at rubidium.dyndns.org> wrote:

> Alex,
> 
> Sure, but is that close-in phase-noise or wideband white noise?
> It matters greatly how it is distributed in frequency.
> 
> Most importantly, is it low enough to recover the clock.
> 
> If it is too high, then one needs to use another VCO.
> 
> In this case, he only wanted to use the 74HCT9046 as a phase comparator and then steer a VCXO, so the 9046s VCO phasenoise would not be relevant.
> 
> The clock recovery PLL only have to have decent phase noise above 8 kHz, as below that it is being suppressed by the loop and replaced by the source (and lower frequency systematics from cabling and ISI). Sure, near 8 kHz it needs to be decent as the suppression isn't perfect.
> 
> Then comes the much narrower PLL.
> 
> Cheers,
> Magnus
> 
> 
> On 04/29/2014 02:21 AM, Alexander Pummer wrote:
>> the CMOS chip: PLL 74HC4046, 7046, 9046,  will have substantial phase
>> noise, particularly close to the higher end of the usable frequency range..
>> 73
>> Alex
>> 
>> On 4/28/2014 1:30 PM, Magnus Danielson wrote:
>>> Chris,
>>> 
>>> On 04/28/2014 04:16 PM, Chris Albertson wrote:
>>>> On Sun, Apr 27, 2014 at 11:41 PM, sg sg <micpreamp at yahoo.de> wrote:
>>>> 
>>>>> Thanks very much for your responses!
>>>>> ..
>>>>> The source is an AK4114 AES/EBU audio receiver, which has both master
>>>>> clock (24.576 MHz) and "word select" rate (48-192 kHz) outputs.
>>>>> Perhaps it
>>>>> is better to run the PLL at the latter? Any disadvantages from this?
>>>> 
>>>> 
>>>> So this is for clock distribution in a studio?   While our eras don't
>>>> care
>>>> about nano seconds or even micro seconds we do care that long of the
>>>> same
>>>> length have exactly the same number of samples.  In other words at a
>>>> given
>>>> times into a track, all tracks have the same number of samples.    I
>>>> think
>>>> what matters in this application is long term stability over days, weeks
>>>> and even years.   So the first step is always to figure out your
>>>> requirements and USE NUMBERS.
>>>> 
>>>> Next.  It is not "either/or"  you can put the PPL at 24..5MHz or 48K
>>>> or you
>>>> can divide by 10 and put the PPL at 2.45Mhz.  or any place in between.
>>>> 
>>>> One question:  Why use the receiver as a clock source?  Most use
>>>> something
>>>> independent like an OX or even Rb then use that to drive a DDS chip.
>>>> 
>>> 
>>> Rb is way overkill. Beyond keeping things in sync to ensure same
>>> sample rate, what is important is jitter but not ppm level wander.
>>> Jitter can kill your listening experience by to ways, one is bit error
>>> rate, causing bits to be incorrect. The second is that it creates
>>> side-bands, which causes issues when you try to achieve 24 bit
>>> resolution, or for that matter 130 dB dynamics. Do read what Julian
>>> Dunn had to discuss on that matter, since he look at what sidebands
>>> would do, considering masking effects of psycho-acoustics etc.
>>> 
>>> Then again, we being time-nuts, overkill is easy to achieve.
>>> We need to be careful about jitter as we re-synthesize and lock things
>>> up. Jitter-peaking as a cause of jitter accumulation, and that leads
>>> to... bit errors and side-bands.
>>> 
>>> Cheers,
>>> Magnus
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