Question

What must be done to block the ac input voltage riding on a dc level?

(a) Use RC network

(b) Use coupling capacitor

(c) Use resistive transducer

(d) None of the mentioned

The question was asked at a job interview.

The question is from Very High Input Impedance Circuit topic in section Operational Amplifier Applications of Linear Integrated Circuits

Answer 1

The correct answer is:

(b) Use coupling capacitor

Explanation:

A coupling capacitor is used to block the DC component of a signal while allowing the AC component to pass through.

• The capacitor's impedance to DC is infinite (open circuit), which effectively blocks the DC level.
• For AC signals, the impedance depends on the signal frequency and capacitor value, allowing the AC component to pass.

This technique is commonly employed in amplifier circuits and other applications where separating AC and DC components is necessary.