*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 immunity to noise. This is primarily due to the design of their input switching threshold.

### Explanation:

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

   - **Reason**: CMOS circuits are designed such that the input switching threshold is approximately half of the power supply voltage. This means that the circuit will switch states when the input voltage is around 50% of the supply voltage. This threshold provides a balanced margin for noise immunity because any noise on the input signal needs to be significant enough to push the voltage past this midpoint to cause an erroneous switch. This makes CMOS circuits less susceptible to noise compared to other logic families.

2. **Why the Other Choices are Incorrect:**

   - **A: Large bypass capacitance is inherent**
     - **Reason**: While bypass capacitors are used to stabilize power supply voltages, they are not inherently part of the CMOS design itself. Bypass capacitance helps reduce power supply noise but is not the primary reason for CMOS noise immunity.

   - **B: The input switching threshold is about twice the power supply voltage**
     - **Reason**: This is incorrect because the input switching threshold cannot be twice the power supply voltage. The threshold must be within the range of the supply voltage, typically around half, not exceeding it.

   - **D: Bandwidth is very limited**
     - **Reason**: Bandwidth limitation is not a factor in noise immunity. CMOS circuits can have a wide range of bandwidths, and this characteristic does not directly contribute to their noise immunity.

### Summary:

The key to CMOS noise immunity lies in its input switching threshold being set at approximately half the power supply voltage. This design choice provides a robust margin against noise, ensuring reliable operation even in the presence of electrical noise.