On 07/05/2014 12:32 AM, Rob wrote:
Eric Weaver wrote:
So pardon my ignorance, what's the hip PLL or at least
counter/phase-detector these days?

Hip these days is not to use a PLL but use an NCO.
Of course there are differences in the spurious and noise output.

Fair enough. The Si570 and 571 look pretty sweet, but are a bit spendy
on something I was hoping to make a bunch of.



However, when still using a PLL and using it for amateur purposes
(small steps relative to the frequency), at least go for a dual-modulus
system. Else the phase comparator has to operate at the frequency of
the channel step, or even at a fraction of that when a fixed prescaler
is required in front of the programmable divider. As the MC145151
at best operates up to 25 MHz, you often will require a prescaler.
A low phase comparator frequency means a slow loop.

Given that it'll power up and stay on channel a long-ish time, that may
not be a bad thing, but point taken. It need not tune every finest step.



The MC145152 is a dual-modulus version. However, note that with a
dual-modulus system it is more complicated to generate the setting
information, probably requiring a microcontroller. Once you are going
to need that, it is easier to use a more modern IC programmed using I2C.



I guess it's time to hunker down and learn to program an Arduino or
Propeller...