I was recently low entropy equations of passive filters, and came across the Extra Element Theorem and all of its uses.
I was wondering if the there is something similar for OP AMP circuits/ Active Filter Circuits?
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\$\begingroup\$ What do you find from googling? \$\endgroup\$– Andy akaCommented Jun 27, 2018 at 14:04
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\$\begingroup\$ Look for Middlebrooks General Feedback Theorem \$\endgroup\$– HKOBCommented Jun 27, 2018 at 14:23
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1\$\begingroup\$ Why do you think, the EEE could be limited to passive filters only? This theorem can be applied to linear active and passive circuits. \$\endgroup\$– LvWCommented Jun 27, 2018 at 14:53
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\$\begingroup\$ I haven't gone through the EEE formally, I have gone through a tutorial which explains its use for passive circuits. \$\endgroup\$– Preetham ReddyCommented Jun 28, 2018 at 17:18
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1 Answer
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Yes, active filters are simply passive filters where you can ignore impedance losses and you don't have to worry about load or source impedance.
Here is an example of turning a transfer function into a "low entropy" state for an active filter
$$ W(s) = \frac{R_2}{-R_1+(-R_2-R_3)C_1R_1s-C_2C_1R_3R_2R_1s^2}$$
to
$$H(s) = -\frac{R_2}{R_1}\frac{1}{1+(R_2+R_3)*C_1s+C_2C_1R_3R_2s^2}$$
Source: https://www.maximintegrated.com/en/app-notes/index.mvp/id/5597
answered Jun 28, 2018 at 5:17
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\$\begingroup\$ Besides the question if "active filters are simply passive filters" I like to mention that for the majority of active filters we must NOT ignore source impedances. \$\endgroup\$– LvWCommented Jun 28, 2018 at 6:33