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Active Filters
32 questions By Tony R. Kuphaldt
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Question 16 of 32
Approximate the voltage gains of this active filter circuit at f = 0 and f = ∞ (assume ideal op-amp behavior):
Approximate the voltage gains of this other “active filter” circuit at f = 0 and f = ∞ (assume ideal op-amp behavior):
What type of filtering function (low pass, high pass, band pass, band stop) is provided by both these filter circuits? Comparing these two circuit designs, which one do you think is more practical? Explain your answer.
Reveal answerThese are both low pass filters. The circuit with the shunt capacitor is the more practical one, because its voltage gain remains finite for all possible input signal frequencies:
Notes:Discuss with your students their methods of determining filter type. How did they approach this problem, to see what type of filter both these circuits were?
Also, discuss with your students the problem of having an amplifier circuit with an unchecked gain (approaching infinity). Ask them what is wrong with obtaining such high voltage gains from any amplifier. Have them describe to you the effect of a huge voltage gain on the integrity of the amplified signal.
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Question 17 of 32
Approximate the voltage gains of this active filter circuit at f = 0 and f = ∞ (assume ideal op-amp behavior):
Approximate the voltage gains of this other “active filter” circuit at f = 0 and f = ∞ (assume ideal op-amp behavior):
What type of filtering function (low pass, high pass, band pass, band stop) is provided by both these filter circuits? Comparing these two circuit designs, which one do you think is more practical? Explain your answer.
Reveal answerThese are both high pass filters. The circuit with the series capacitor is the more practical one, because its voltage gain remains finite for all possible input signal frequencies:
Notes:Discuss with your students their methods of determining filter type. How did they approach this problem, to see what type of filter both these circuits were?
Also, discuss with your students the problem of having an amplifier circuit with an unchecked gain (approaching infinity). Ask them what is wrong with obtaining such high voltage gains from any amplifier. Have them describe to you the effect of a huge voltage gain on the integrity of the amplified signal.
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Question 18 of 32
Identify the function of this active filter:
It is low pass, high pass, band pass, or band stop? Explain your answer.
Reveal answerThis is a band pass filter circuit.
Notes:Discuss with your students their methods of determining filter type. How did they approach this problem, to see what type of filter this circuit was? Determining the identify of a “band-” filter is more difficult than with a low- or a high- pass filter circuit, because the behavior is roughly the same at both extremes of the frequency range.
