Figure 2-8.
Piezoelectric crystal.
(1) One type of crystal-controlled oscillator that uses the crystal's series
resonant feature for frequency determination is shown in A of figure 2-9.
For variety a PNP transistor is shown, so biases are negative.
This
shunt-fed crystal-controlled oscillator is basically a tickler-coil type.
Regenerative feedback is obtained by transformer action.
The collector
tank is tuned to the series resonant frequency of the crystal.
Because
the crystal is very selective, it greatly improves the frequency stability
of the signal generated.
(2) Another crystal-controlled oscillator is shown in B of figure 2-8.
You
should recognize it as a Colpitts type.
The inductance required to
resonate with C1 and C2 is provided by the crystal.
(3) These are but two of a wide variety of ways to use crystals for frequency
control of oscillators.
The main advantage of crystals is their
stabilizing influence.
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