*Question E7H12:
Which of the following ensures that a crystal oscillator operates on the frequency specified by the crystal manufacturer?*  

*Correct Answer is  B: Provide the crystal with a specified parallel capacitance*  

### AI Response: (may contain errors)  

To ensure that a crystal oscillator operates on the frequency specified by the crystal manufacturer, you need to provide the crystal with a specified parallel capacitance. Here's why:

1. **Correct Answer: B: Provide the crystal with a specified parallel capacitance**

   - **Explanation**: Crystals are designed to operate at a specific frequency when a certain load capacitance is applied. This load capacitance is specified by the manufacturer and is crucial for the crystal to oscillate at its intended frequency. The load capacitance affects the resonant frequency of the crystal, and using the correct value ensures accurate frequency operation.

2. **Why the Other Choices are Incorrect:**

   - **A: Provide the crystal with a specified parallel inductance**
     - Inductance is not typically used to set the operating frequency of a crystal oscillator. Crystals are primarily affected by capacitance, not inductance, for frequency determination.

   - **C: Bias the crystal at a specified voltage**
     - Crystals do not require a specific bias voltage to operate at their specified frequency. The frequency is determined by the mechanical properties of the crystal and the load capacitance, not by voltage biasing.

   - **D: Bias the crystal at a specified current**
     - Similar to voltage, the current bias does not determine the operating frequency of a crystal. The frequency is primarily influenced by the load capacitance.

3. **Useful Formula:**

   - The frequency of a crystal oscillator can be affected by the load capacitance ($C_L$). The manufacturer specifies a load capacitance that ensures the crystal operates at its nominal frequency. The formula for the load capacitance is:

     $$ C_L = \frac{C_1 \times C_2}{C_1 + C_2} + C_{stray} $$

     where:
     - $C_1$ and $C_2$ are the capacitors used in the oscillator circuit.
     - $C_{stray}$ represents any stray capacitance in the circuit.

By ensuring the correct load capacitance, you can maintain the crystal's specified frequency.