Re: Phase or frequency modulation?

Liz Tuddenham <liz@poppyrecords.invalid.invalid> wrote:

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
 
 

... The crystal mode is a mass-spring
oscillation, so an instantaneous change in the spring constant causes an
instantaneous change of frequency.
 
There’s no need for the resonant energy to die out, unlike the case of
external forcing, where a change in the forcing frequency takes on the
order of Q cycles to change the response.

 
Could I ask you to explain this a bit more please.  Where is the
'spring' that is variable?
 
 

The spring is the mechanical stiffness of the quartz, plus the
piezoelectric force caused by the interaction with the external circuit.
The mass is the mass. ;)

Dorking the load capacitance slows down or speeds up the piezo restoring
force.

Looking at it this way, i.e. as a simple harmonic oscillator, introduces
some small error, because there is a small acoustic delay involved. It’s
tiny compared with a SAW resonator, however.

I had this forcefully brought to my attention long ago, when my old
colleague Doug Smith invented a super fast atomic force microscope by
turning the vibrating cantilever into an oscillator.

Mine was way more sensitive, but his was, like, 200 times faster.  Really a
smart guy.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs  Principal Consultant  ElectroOptical Innovations LLC /
Hobbs ElectroOptics  Optics, Electro-optics, Photonics, Analog Electronics