Deep Dive: E6C06
The correct answer is C: The input switching threshold is about half the power supply voltage. Why do CMOS digital integrated circuits have high immunity to noise on the input signal or power supply is that the input switching threshold is about half the power supply voltage. This gives maximum noise margin. For amateur radio operators, this is important for digital circuits. Understanding this helps when using CMOS.
Why Other Answers Are Wrong
Option A: Incorrect. Large bypass capacitance inherent isn't the reason - input threshold at half supply gives noise immunity. Bypass capacitance isn't the reason. Option B: Incorrect. Input switching threshold about twice power supply voltage isn't correct - it's about half. Twice isn't correct. Option D: Incorrect. Bandwidth very limited isn't the reason - input threshold at half supply gives noise immunity. Bandwidth isn't the reason.
Exam Tip
CMOS noise immunity = input switching threshold about half power supply voltage. Think 'C'MOS 'N'oise 'I'mmunity = 'C'enter 'N'oise margin (half supply). This gives maximum noise margin. Not bypass capacitance, not twice supply, not bandwidth - just half supply threshold.
Memory Aid
CMOS noise immunity = input switching threshold about half power supply voltage. Think 'C'MOS = 'H'alf supply threshold. This gives maximum noise margin. Important for digital circuits.
Real-World Example
CMOS digital integrated circuits have high immunity to noise: It's because the input switching threshold is about half the power supply voltage. This provides maximum noise margin - equal distance from both supply rails. This is the reason - half supply threshold.
Source & Coverage
Question Pool: 2024-2028 Question Pool
Subelement: E6C
Reference: 2024-2028 Question Pool · E6 - Circuit Components
Key Concepts
Verified Content
Question from the official FCC Extra Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the E6C topic.