[time-nuts] crunching numbers from XOR phase detector
ehydra at arcor.de
Wed Jan 4 23:23:46 UTC 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
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.
Brian Justin schrieb:
> Not yet, but I guess I will now!
> ----- 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.
> 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
>> is at or very close to zero. Some versions of the chip claim to have
>> that dead-zone. But it's still there to some degree, at least in all the
>> versions I have tried.
>> -Brian, WA1ZMS
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