Analog Circuits Cookbook

256 Analog Circuits Cookbook

Figure

8.27 Equivalent circuit of a quartz crystal, and the variation of its imped-

ance in the vicinity of series resonance, including parallel resonance. Diagram (b)

shows how ignoring C

0

series resonance can provide a very narrow passband

when working between source and load impedances comparable to its equivalent

series resistance

Figure 8.27(a) shows the equivalent circuit of a crystal, C

Q

being the

capacitance between the two electrodes plus the strays due to mounting

and encapsulation. L

1?

and R^ are the electrical equivalents of the crystal's

motional inductance and capacitance, and damping . Although th