Difference between revisions of "Second Order Active Filters"
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The high input impedance provided by an op amp circuit protects the instrument providing the signal from passing excessive current which could cause a voltage drop in the measurement signal or damage to the instrument itself. |
The high input impedance provided by an op amp circuit protects the instrument providing the signal from passing excessive current which could cause a voltage drop in the measurement signal or damage to the instrument itself. |
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Because the filter is second order, the rolloff after the cutoff frequency on a bode plot of a low pass filter for example, is -40 dB/decade as opposed to -20 dB/decade for a first order (RC) filter which means significantly greater attenuation outside the pass band and a sharper cutoff. This can be very useful if the noise frequency is close to the desired signal frequency. |
Because the filter is second order, the rolloff after the cutoff frequency on a bode plot of a 2nd order low pass filter for example, is -40 dB/decade as opposed to -20 dB/decade for a first order (RC) filter which means significantly greater attenuation outside the pass band and a sharper cutoff. This can be very useful if the noise frequency is close to the desired signal frequency. |
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[[Image:2ndOrderFilterDiagrams.gif]] |
[[Image:2ndOrderFilterDiagrams.gif]] |
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(http://ourworld.compuserve.com/homepages/Bill_Bowden/opamp.htm) |
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Where the cutoff frequency for both high and low pass filters in Hz is: |
Where the cutoff frequency for both high and low pass filters in Hz is: |
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'''External Links''' |
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References: |
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http://en.wikipedia.org/wiki/Sallen_Key_filter |
http://en.wikipedia.org/wiki/Sallen_Key_filter |
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Latest revision as of 15:45, 14 December 2008
2nd order active filtering has two main advantages:
- High impedance input, low impedance output
- greater attenuation at high range (-40dB/decade as opposed to -20dB/decade for RC filter)
The high input impedance provided by an op amp circuit protects the instrument providing the signal from passing excessive current which could cause a voltage drop in the measurement signal or damage to the instrument itself.
Because the filter is second order, the rolloff after the cutoff frequency on a bode plot of a 2nd order low pass filter for example, is -40 dB/decade as opposed to -20 dB/decade for a first order (RC) filter which means significantly greater attenuation outside the pass band and a sharper cutoff. This can be very useful if the noise frequency is close to the desired signal frequency.
(http://ourworld.compuserve.com/homepages/Bill_Bowden/opamp.htm)
Where the cutoff frequency for both high and low pass filters in Hz is:
External Links
