Test Your EQ (Engineering Quotient)

EQ #72

Suppose you know that a nominal 10.000-MHz crystal has a 9.996490-MHz series-resonant frequency and a 10.017730-MHz parallel-resonant frequency. You also know that its equivalent series capacitance is 27.1 fF. How can you calculate the value of its parallel capacitance?

First, calculate the crystal’s equivalent inductance, based on the series-resonant frequency:

Next, calculate the capacitance required to resonate with that inductance at the parallel-resonant frequency:

Finally, calculate the value of CPAR required to give that value of capacitance when in series with CSER:

Note that all three equations can be combined into one, and this reduces to:

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EQ #72

by Circuit Cellar Staff time to read: <1 min