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Passive Filter Circuits
44 questions By Tony R. Kuphaldt
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Question 25 of 44
The cutoff frequency, also known as half-power point or -3dB point, of either a low-pass or a high-pass filter is fairly easy to define. But what about band-pass and band-stop filter circuits? Does the concept of a “cutoff frequency” apply to these filter types? Explain your answer.
Reveal answerUnlike low-pass and high-pass filters, band-pass and band-stop filter circuits have two cutoff frequencies (fc1 and fc2)!
Notes:This question presents a good opportunity to ask students to draw the Bode plot of a typical band-pass or band-stop filter on the board in front of the class to illustrate the concept. Don’t be afraid to let students up to the front of the classroom to present their findings. It’s a great way to build confidence in them and also to help suppress the illusion that you (the teacher) are the Supreme Authority of the classroom!
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Question 26 of 44
Plot the typical response of a band-pass filter circuit, showing signal output (amplitude) on the vertical axis and frequency on the horizontal axis:
Also, identify and label the bandwidth of the circuit on your filter plot.
Reveal answer
The bandwidth of a band-pass filter circuit is that range of frequencies where the output amplitude is at least 70.7% of maximum:
Notes:Bandwidth is an important concept in electronics, for more than just filter circuits. Your students may discover references to bandwidth of amplifiers, transmission lines, and other circuit elements as they do their research. Despite the many and varied applications of this term, the principle is fundamentally the same.
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Question 27 of 44
Plot the typical response of a band-stop filter circuit, showing signal output (amplitude) on the vertical axis and frequency on the horizontal axis:
Also, identify and label the bandwidth of the circuit on your filter plot.
Reveal answer
The bandwidth of a band-stop filter circuit is that range of frequencies where the output amplitude is reduced to at least 70.7% of full attenuation:
Notes:Bandwidth is an important concept in electronics, for more than just filter circuits. Your students may discover references to bandwidth of amplifiers, transmission lines, and other circuit elements as they do their research. Despite the many and varied applications of this term, the principle is fundamentally the same.
