*Question G6A07:
What are the operating points for a bipolar transistor used as a switch?*  

*Correct Answer is  A: Saturation and cutoff*  

### AI Response: (may contain errors)  

In a bipolar transistor used as a switch, the operating points are:

### Correct Answer: Saturation and Cutoff

1. **Saturation**: 
   - In saturation, both the base-emitter and base-collector junctions are forward-biased.
   - The transistor acts like a closed switch, allowing maximum current to flow from collector to emitter.
   - The voltage across the collector-emitter ($V_{CE}$) is minimal, close to zero.

2. **Cutoff**: 
   - In cutoff, both the base-emitter and base-collector junctions are reverse-biased.
   - The transistor acts like an open switch, preventing current flow from collector to emitter.
   - The collector current ($I_C$) is essentially zero.

### Why Other Choices Are Incorrect:

- **The active region (between cutoff and saturation)**:
  - This is where the transistor operates as an amplifier, not as a switch. In this region, the transistor is partially on, allowing it to amplify signals.

- **Peak and valley current points**:
  - These terms are not typically used to describe the operation of a bipolar transistor as a switch. They are more relevant to devices like tunnel diodes.

- **Enhancement and depletion modes**:
  - These terms apply to field-effect transistors (FETs), not bipolar junction transistors (BJTs). Enhancement and depletion describe how the channel conductivity is controlled in FETs.

### Summary:

For switching applications, a bipolar transistor is either fully on (saturation) or fully off (cutoff), making these the correct operating points for a switch.