[time-nuts] Injection Locking

Murray Greenman Murray.Greenman at rakon.com
Tue Feb 2 21:28:38 UTC 2010


Frank,

As Bruce suggests, you can in theory lock any rational number ratio,
including 11/5 and 21/5. However, the locking gain drops off as the
ratio becomes more extreme, and thus the lock range and potential
stability are degraded.

Yes, you could certainly use a regenerative divider to generate 6MHz or
7MHz, but why not use another IL oscillator? Simply make a 6MHz gate
oscillator (common micro crystal) and lock it to 2MHz, divided from
10MHz, then use that to lock 42MHz. If you use Johnson decade counter as
divider (e.g. 74HC4017), you get a nice 100ns wide 2MHz pulse to lock
to.

In my experience locking higher frequencies to lower ones is easier if
the reference consists of a pulse with width rather less than the period
of the higher frequency, although this depends on how you inject.

You'll need to buffer and shape the 6MHz to lock the 42MHz oscillator.
Good idea, build a bunch of gate oscillators and experiment. I suggest
you also try directly locking 42MHz to 2MHz, in order to determine the
lock range.

I know from experience at 2MHz to 10MHz (5/1) the lock range is immense,
far more than the thermal drift of the 10MHz oscillator, and so I have a
very phase stable result. I used mine to GPS lock a 2MHz OCXO, using a
micro running at 10MHz, and I injection locked the 10MHz micro clock to
the 2MHz, and so needed good phase stability.

Not a micro or ASIC in sight!

73,
Murray Zl1BPU




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