Which of the following must be done to insure that a crystal oscillator provides the frequency specified by the crystal manufacturer?
A. Provide the crystal with a specified parallel inductance
B. Provide the crystal with a specified parallel capacitance
C. Bias the crystal at a specified voltage
D. Bias the crystal at a specified current
A crystal oscillator is a high-stability device used to provide, well, oscillations in a circuit. It is, basically by definition, a type of RLC tank circuit (we talked about that some here.) Since the internal components of the oscillator are fixed, you need a way to provide the proper “load” to the circuit to complete it and “tune” it to provide the necessary impedance. That’s where a “load capacitor” comes in.
You might have then guessed that the answer is B. Provide the crystal with a specified parallel capacitance.
There are a lot of complex things going on, and I recommend reading the following to maybe try and get a better handle on it:
Also note that the question is basically very generalized, there are a lot of other factors that can come into play, as there are many different types of oscillators and ways to properly tune them.