Analog and electronic circuits
What does the "−3 dB" point in a filter's frequency response represent?
- AThe point where power falls to about 1/2 (voltage to about 0.707 times)
- BThe point where the voltage is exactly 1/3
- CThe point where the power becomes zero
Show answer and explanation
Answer: A. The point where power falls to about 1/2 (voltage to about 0.707 times)
−3 dB corresponds to about 1/2 in power and 1/√2 ≈ 0.707 in voltage. In filters, this point is taken as the cutoff frequency and serves as the boundary of the passband.
- A. Correct. Power halves and voltage falls to about 0.707.
- B. A voltage of 1/3 is about −9.5 dB.
- C. Zero power corresponds to −∞ dB.