*Question E7C09:
What is a crystal lattice filter?*  

*Correct Answer is  D: A filter for low-level signals made using quartz crystals*  

### AI Response: (may contain errors)  

A crystal lattice filter is a type of filter used in radio frequency applications, particularly for processing low-level signals. Here's why the correct answer is correct and why the other choices are incorrect:

1. **Correct Answer: D - A filter for low-level signals made using quartz crystals**

   - **Explanation**: Crystal lattice filters are designed to provide very high selectivity and stability, which makes them ideal for filtering low-level signals. They use quartz crystals because of their high quality factor (Q), which allows for narrow bandwidths and precise frequency control. This makes them suitable for applications like intermediate frequency (IF) stages in receivers.

2. **Why the other choices are incorrect**:

   - **Choice A: A power supply filter made with interlaced quartz crystals**
     - **Explanation**: Power supply filters typically use capacitors and inductors to smooth out voltage fluctuations. Quartz crystals are not used in power supply filters because they are designed for frequency control, not voltage regulation.

   - **Choice B: An audio filter made with four quartz crystals that resonate at 1 kHz intervals**
     - **Explanation**: Audio filters generally do not use quartz crystals because the frequencies involved are much lower than those where quartz crystals are effective. Quartz crystals are used for radio frequencies, not audio frequencies.

   - **Choice C: A filter using lattice-shaped quartz crystals for high-Q performance**
     - **Explanation**: While the term "lattice" is used, it refers to the configuration of the filter circuit, not the physical shape of the crystals. The crystals themselves are not lattice-shaped; they are typically cut in specific orientations to achieve desired frequency characteristics.

In summary, crystal lattice filters are specialized for handling low-level RF signals with high precision, making them unsuitable for power supply or audio applications.