Re: Yo! RF dudes!

John Larkin <jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

We have one product that uses a 600 MHz gated oscillator, using a
coaxial ceramic resonator and a mmic.

John

I used the gated oscillator I posted earlier in an octave-bandwidth vco
running from 350MHz to 700MHz to measure hard disk error rate. It went
directly from SPICE to a production pcb. Since the oscillator phase noise
is part of the measurement, a low value is desirable. I believe it was
about 54ps rms. The oscillator jitter remains the same when it is divided
down, but then it is much smaller part of a cycle so the vco noise became
insignificant compared to the readback signal.

How long does the ceramic resonator take to come up to amplitude? If it's
too slow, can you goose it? That might be the solution to your 50Mhz gated
oscillator problem. Run the oscillator at a high frequency with a high Q
element, then divide down. That should give much better phase noise than
running at 50Mhz with a low Q surface-mount inductor. You should be able to
pull the ceramic resonator enough to phase lock with your reference. That
could solve your tempco problem and give better performance.

I've heard of people starting a crystal oscillator in one cycle. I don't
know how they do it without damaging the crystal, but it might be worth
looking at.

Regards,

Mike Monett

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