*Question E7H05:
How is positive feedback supplied in a Pierce oscillator?*  

*Correct Answer is  D: Through a quartz crystal*  

### AI Response: (may contain errors)  

In a Pierce oscillator, positive feedback is supplied through a quartz crystal. Here's why:

1. **Correct Answer: Through a quartz crystal**
   - A Pierce oscillator uses a quartz crystal to provide the necessary positive feedback. The crystal acts as a frequency-selective element, ensuring that the oscillator operates at a stable frequency. The crystal's properties allow it to provide the phase shift and gain needed for oscillation.

2. **Why the other choices are incorrect:**
   - **A: Through a tapped coil**
     - A tapped coil is typically used in LC oscillators, such as Hartley oscillators, to provide feedback. It is not used in Pierce oscillators, which rely on the crystal for feedback.
   - **B: Through link coupling**
     - Link coupling is a method of transferring energy between circuits, often used in RF amplifiers or transformers, not in providing feedback in a Pierce oscillator.
   - **C: Through a neutralizing capacitor**
     - A neutralizing capacitor is used to cancel unwanted capacitance or feedback in amplifiers, not to provide positive feedback in oscillators.

3. **Useful Concepts:**
   - The Pierce oscillator configuration typically includes an amplifier (like a transistor or an op-amp) and a quartz crystal. The crystal provides both the frequency control and the feedback path necessary for sustained oscillations.
   - The crystal's high Q factor ensures that the oscillator has excellent frequency stability and low phase noise.

Understanding the role of the quartz crystal in a Pierce oscillator is crucial for recognizing how it differs from other oscillator types that use different feedback mechanisms.