On 12/31/19 8:45 AM, Richard (Rick) Karlquist wrote:
You need to determine your requirements for phase
noise. You also need to coordinate this PLL with
the phase noise of the 3.125 GHz PLL, which will
need its own VCO.
The best VCXO's I have found are from Abracon,
COTS in distribution (DigiKey, etc) for only
about $25.
+1 for Abracon - excellent phase noise performance for off the shelf
devices that are cheap and *in stock*
Lucky for you that 125 MHz is a
standard frequency for them. At 3.125 GHz there are several
vendors such as Z-comm to browse. You need
to find one with 3.125 GHz output frequency and then
it needs to be low phase noise. May not be
available. It's just the luck of the draw
as to what they choose to make.
Any PLL chip with a divider and on board phase
detector will give only mediocre performance
(which may be good enough for you). And it
will require a microcontroller to load the
gazillion registers onboard (no strapping).
This *is* the problem these days. A parallel load PLL is almost unheard
of today.
You might look at the (formerly Hittite) HMC parts at Analog Devices -
low phase noise on chip VCOs, and/or low noise divider that can divide
your 3.125 down. Hittite used to have a fixed Divide By N that could do
your 3125 to 125 (divide by 25).
A quick glance at AD's website looks like the HMC705 can do divide by 5,
so you could cascade a couple of these. It doesn't look like the "divide
by anything up to 56" part still exists, at least that will take 3.125.
You might also find a HMC part with a VCO to cover your range.
If you're doing a one-off, there are eval boards with SMA connectors,
etc. available.
For
high performance, you need a conventional
multiplier from 10 MHz to, say, 120 MHz and
then mix down to 5 MHz and use a mixer as
a phase detector. You can divide the 10 MHz
by 2 using a 74AC74.
You decide: performance vs cost/simplicity.
Rick N6RK
On 12/31/2019 8:01 AM, Dan Kemppainen 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.
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.
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