*Question E7B02:
What is a Class D amplifier?*  

*Correct Answer is  A: An amplifier that uses switching technology to achieve high efficiency*  

### AI Response: (may contain errors)  

A Class D amplifier is a type of amplifier that uses switching technology to achieve high efficiency. Here's why this is the correct answer and why the other choices are incorrect:

1. **Correct Answer: A - An amplifier that uses switching technology to achieve high efficiency**
   - Class D amplifiers operate by rapidly switching the output devices (usually transistors) on and off. This switching creates a pulse-width modulated (PWM) signal that is then filtered to produce the desired audio output. The key advantage of this method is high efficiency, often exceeding 90%, because the output devices are either fully on or fully off, minimizing the time they spend in the linear region where power dissipation is highest.

2. **Incorrect Choices:**
   - **B: A low power amplifier that uses a differential amplifier for improved linearity**
     - This describes a different type of amplifier, often used in Class A or Class AB designs, where linearity is a priority over efficiency. Class D is not primarily concerned with linearity in the same way.
   - **C: An amplifier that uses drift-mode FETs for high efficiency**
     - Drift-mode FETs are not a standard component of Class D amplifiers. The efficiency in Class D comes from the switching operation, not from a specific type of FET.
   - **D: An amplifier biased to be relatively free from distortion**
     - This describes amplifiers like Class A, which are biased to operate in the linear region to minimize distortion. Class D amplifiers focus on efficiency rather than minimizing distortion through biasing.

**Key Points:**
- Class D amplifiers are known for their high efficiency due to the switching operation.
- They are not primarily designed for low distortion or improved linearity, which are characteristics of other amplifier classes.
- The efficiency of Class D amplifiers makes them ideal for applications where power conservation is important, such as in portable audio devices.