*Question E6C06:
Why do CMOS digital integrated circuits have high immunity to noise on the input signal or power supply?*  

*Correct Answer is  C: The input switching threshold is about half the power supply voltage*  

### AI Response: (may contain errors)  

CMOS (Complementary Metal-Oxide-Semiconductor) digital integrated circuits are known for their high noise immunity, primarily due to their input switching threshold characteristics.

### Correct Answer: C
**The input switching threshold is about half the power supply voltage.**

- **Explanation**: In CMOS circuits, the input switching threshold is typically around $V_{DD}/2$, where $V_{DD}$ is the power supply voltage. This means that the circuit can tolerate a range of input voltages around this threshold without misinterpreting the signal. This characteristic allows CMOS circuits to effectively distinguish between high and low logic levels, even in the presence of noise.

### Why the Other Choices are Incorrect:

- **A: Large bypass capacitance is inherent**  
  - **Explanation**: While bypass capacitors can help stabilize the power supply and filter out noise, they do not directly contribute to the input signal's noise immunity. Bypass capacitance is more about power supply stability than input signal integrity.

- **B: The input switching threshold is about twice the power supply voltage**  
  - **Explanation**: This statement is incorrect because the input switching threshold is not above the power supply voltage. If it were, the circuit would not function correctly, as it would require an input voltage that exceeds the supply voltage to switch states.

- **D: Bandwidth is very limited**  
  - **Explanation**: CMOS circuits can have a wide bandwidth depending on their design and application. Limited bandwidth does not inherently provide noise immunity; rather, it can affect the speed of operation. Noise immunity is more related to the input threshold levels than to bandwidth.

### Summary
The key to understanding CMOS noise immunity lies in the input switching threshold being around half the power supply voltage, allowing for effective discrimination between logic levels amidst noise. This characteristic is what makes CMOS technology robust in noisy environments.