[time-nuts] crunching numbers from XOR phase detector

ehydra ehydra at arcor.de
Wed Jan 4 18:23:46 EST 2012


The XOR phase comparator is without feed-back and that simply means no 
dead-zone. This is consistent with literature on XOR PDs.

It will of course have non-linearity which is improving with speed of 
the process technology. A 74HC4046 will be better than a CD4046.
BUT the low-frequency noise is inversely proportional to channel-length 
of the used MOSFETs. So for time-nuts interests a slower CD4046 can be 
better.

The other 4046 phase comparators are made of flip-flops where the 
dead-zone is proportional to gate-delay.

For ultimate performance one have to use a classical DRM.

- Henry


Brian Justin schrieb:
> Not yet, but I guess I will now!
> Thanks!
> 
> -Brian
> 
> 
> 
> 
> 
> ----- Original Message ----
> From: Orin Eman <orin.eman at gmail.com>
> To: Discussion of precise time and frequency measurement <time-nuts at febo.com>
> Sent: Wed, January 4, 2012 12:59:12 PM
> Subject: Re: [time-nuts] crunching numbers from XOR phase detector
> 
> Have you tried the 74HCT9046?  They claim no dead zone.  Note - seems to be
> HCT only.
> 
> Orin.
> 
> On Wed, Jan 4, 2012 at 9:32 AM, Brian Justin <wa1zms at att.net> wrote:
> 
>> Be very careful of the FPD in the 4046. It has a dead-zone when the phase
>> error
>> is at or very close to zero.  Some versions of the chip claim to have
>> "improved"
>> that dead-zone. But it's still there to some degree, at least in all the
>> versions I have tried.
>>
>> -Brian, WA1ZMS
>>

-- 
ehydra.dyndns.info




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