On Fri, 29 Jul 2005 12:33:53 -0700, "John Smith"
wrote:

Ham op:

Just drew the circuit of a xtal in the feedback of a high precision op amp
circuit... hmmm, could be colpitts--but can't see the resemblance...

Just drew the circuit of an xtal chucked in the feedback line of a set of logic
gates... hmmm, that could be colpitts too, but again, can't see the
resemblance...

Draw a transistor (FET, or triode) with a capacitor from collector
(drain, plate) to emitter (source, cathode), an inductor from
collector to base (gate, grid), and a capacitor from base to emitter.

Ground the emitter and everything connected to it and take the output
from the collector. You have a Pierce. Replace the inductor with a
crystal and you have a Pierce oscillator with the crystal operating in
the anti-resonant mode.

Ground the collector and everything connected to it and take the
output from the emitter. You have a Colpitts. Replace the inductor
with a crystal and you have a Colpitts oscillator with the crystal
operating in the anti-resonant mode.

Insert a crystal between the emitter and the two capacitors connected
to it and take the output from the emitter and you have a crystal
oscillator operating at series (or overtone) resonance.

Stick a varactor in there someplace and you have a VCO or VCXO.

Clapp, Vacker, Franklin, Butler.... they are all just variations on an
old theme.