Series Parallel Resonance.
The circuit shown below has both series and parallel resonance.
Applet below show the behaviour of the Impedance with
(100.0, 102.0, 2.5, 1.0, 99.999, 1.0, na, 375, na, 10.0)
This shows that the reactance(Cyan) has 2 zeros at the series and
parallel resonant frequencies. The lower resonant frequency is
series resonant(minimum resistance and maximum admittance). The
higher frequency is parallel resonant with maximum impedance and
minimum admittance. The resonant frequencies are shown on the applet.
Setting parameters to
(100.0, 102.0, 2.5, 1.0, 99.999, 1.0, na, 375, na, 1.5) and changing
Cp shows that the upper frequency can be changed by Cp.
This is the equivalent circuit of a quartz crystal, although the
parameters may be very different, the behaviour is the same. The
crystal can be "tuned" by varying a small capacitor in parallel with it.
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COPYRIGHT © 2007 Cuthbert A. Nyack.