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Active Filters


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A2

Active Filters

Inverting Op-Amp First Order Active Filters

Low Pass - Treble Cut

Filter-Low-Pass-Active-Cct.gif

  • For DC and low frequencies, the capacitor has no effect.
  • The DC and low frequency gain = -Rf / R1.
  • Well above the breakpoint frequency, the capacitor
    reactance is very low.
  • At high frequencies, the gain drops to zero due
    to the negative feedback through the capacitor.
  • The input resistance equals R1.

Treble Boost

Filter-Treble-Boost-Active-Cct.gif

  • At low frequencies, the capacitor has no effect.
  • At low frequencies, the gain = -Rf / R1.
  • At high frequencies the capacitor reduces R1.
  • At high frequencies the gain increases.

High Pass - Bass Cut

Filter-High-Pass-Active-Cct.gif

  • The capacitor blocks DC and low frequencies.
  • The capacitor passes high frequencies easily.
  • The amplifier provides gain.
  • DC and low frequencies the gain = 0.
  • Well above the breakpoint frequency, the gain = -Rf / R1.

Bass Boost

Filter-Low-Pass-Active-Cct.gif

  • For DC and low frequencies, the capacitor has no effect.
  • Rf must be large.
  • At low frequencies the gain is large = -Rf / R1.
  • At high frequencies, Xc is low so the gain drops to zero.
  • The input resistance equals R1

Breakpoint Frequency Calculations

 

 

 

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