Difference between revisions of "Second Order Active Filters"
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Because the filter is second order, the rolloff before/after the cutoff frequency or frequencies on a bode plot 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 before/after the cutoff frequency or frequencies on a bode plot 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]] |
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The transfer function |
The transfer function |
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Revision as of 18:42, 8 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 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 before/after the cutoff frequency or frequencies on a bode plot 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.
The transfer function
