Question
What is the equivalent circuit of a quartz crystal?
Answer Options
- A) Series RLC in parallel with a shunt C representing electrode and stray capacitance
- B) Parallel RLC, where C is the parallel combination of resonance capacitance of the crystal and electrode and stray capacitance
- C) Series RLC, where C is the parallel combination of resonance capacitance of the crystal and electrode and stray capacitance
- D) Parallel RLC, where C is the series combination of resonance capacitance of the crystal and electrode and stray capacitance
Correct Answer: A
Explanation
A quartz crystal, when packaged between two electrodes, behaves electrically like a very high-Q resonant circuit due to the piezoelectric effect. To model its behavior accurately near its resonant frequency, an equivalent circuit is used that accounts for both the mechanical (motional) resonance and the electrical parasitics of the mounting.
The equivalent circuit of a quartz crystal consists of a series RLC network (representing the mechanical resonance and loss of the crystal itself) in parallel with a shunt C (representing the static capacitance of the metal electrodes and the crystal packaging stray capacitance). This combination allows the crystal to exhibit both a series resonant frequency (low impedance) and a slightly higher parallel resonant frequency (high impedance).
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