[time-nuts] PLL suggestions

[Joseph Gwinn]

On Tue, 31 Dec 2019 12:00:02 -0500, time-nuts-request at lists.febo.com 
wrote:
Re: time-nuts Digest, Vol 185, Issue 39

> ------------------------------
> 
> Message: 7
> Date: Tue, 31 Dec 2019 11:01:10 -0500
> From: Dan Kemppainen <dan at irtelemetrics.com>
> To: time-nuts at lists.febo.com
> Subject: [time-nuts] PLL suggestions
> Message-ID: <48e038dd-d78f-4dbc-579e-3de5b5fb8120 at irtelemetrics.com>
> Content-Type: text/plain; charset=utf-8; format=flowed
> 
> Hi All,
> 
> We've got a project going on where we need a 125MHz clock that should be 
> locked to 10MHz. I'm considering an on board 10MHz oscillator and 
> external 10MHz input to utilize an external standard to lock the 125MHz 
> which would PLL a 125MHz source.
> 
> The 125MHz becomes a reference for 3.125Ghz, as well as logic running at 
> 125Mhz. (Currently this system is running on small 125MHz TCXO.) 
> Basically we need a reasonably clean 125MHz signal, but locked to 10Mhz 
> for frequency reference.
> 
> We've identified a few VCXO's that seem to be low noise and are small 
> enough. The 10Mhz is easy enough. However my stumbling block is a simple 
> PLL.
> 
> What I'm looking for is a simple, small PLL chip. Something with 
> external analog loop filter components to allow easy tweaking would be 
> preferred.
> 
> In my perfect world, this chip would be a COTS part, with pin strappable 
> divider configuration or similarly simple hardware configuration. An OTP 
> device would work as well, as would one with it's own memory and 
> external programmer. If necessary a small PIC or similar could be used 
> to configure the PLL, but that's one chip which would be nice to avoid.
> 
> Smaller compact package SMT parts are fine. This is going on a board 
> with lots of SMT components, leadless flat pack devices and BGA's, so 
> smaller is better.
> 
> If any of you have any suggestions, I'd appreciate it.
> 
> Happy new year!
> Dan
> 

This sounds like an Ethernet over fiber application.  If so, the 
phase-noise requirements are not all that stringent, and there are many 
COTS components available.  If I recall, Texas Instruments makes a 
"clock cleaner" IC that can be used here.

Joe Gwinn