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A load capacitor, CL, changes
not only the frequency (see chapter 3), but also the frequency vs.
temperature characteristic. Shown
above are the f vs. T characteristics of the same resonator with and without
a CL. The CL
rotates the f vs. T curve as if the angle of cut had been lowered (because
the combined effect of the resonator and CL lowers the effect of
piezoelectricity, as explained in the reference below). So, the CL raises the frequency
at all temperatures (the curve with fL has been vertically
displaced for clarity), and it also rotates the f vs. T to a lower apparent
angle of cut, i.e., it reduces the turning-point-to-turning-point frequencies
and temperatures.
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