[time-nuts] PLL suggestions

[Bob kb8tq]

Hi

If you are talking about a conventional PLL, the days of pin programable single chip
devices are long gone. Indeed they didn’t last long “back in the day”. The most common
answer is to hook up a cheap micro to shoot the registers. You could also do it with an
FPGA. A lot depends on what is already in the system. 

With logic, GHz, and a PLL involved, isolation to keep crud down will be part of the 
answer …..

Bob

> On Dec 31, 2019, at 11:01 AM, Dan Kemppainen <dan at irtelemetrics.com> wrote:
> 
> 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
> 
> 
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