Engineering Board Exam Reviewer · Passive Filters · medium
The gain plot of a first-order RC low-pass filter is shown (the red dot marks the cutoff frequency). If a 3 V rms signal at 10 kHz is applied, what is the approximate output voltage?
- 0.299 V
- 2.12 V
- 0.948 V
- 0.03 V
Answer
A. 0.299 V
Solution
The cutoff is fc=1 kHz, so 10 kHz is one decade above it. A first-order low-pass rolls off at -20 dB/decade, giving about -20 dB at 10 kHz (read from the plot). VoutVin=10-20/20 0.1, so Vout (3)(0.1)=0.299 V.
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