Active Filters - Low Pass Electronic Circuits

Active Filters: Low Pass
Active Filter -- Main Page
Last Updated on: Friday, March 23, 2012 04:35 PM

Circuits Designed by Dave Johnson, P.E. :
3KHz LOW PASS FILTER PLUS AUDIO AMP This circuit uses a switched capacitor filter IC from National Semiconductor to filter signals with frequencies higher than the 3KHz needed for voice audio. The schematic includes an audio amplifier that is designed to drive a standard audio head phone. The circuit is described in more detail in the receiver section of Dave Johnson's Handbook of Optical Through the Air Communications. (this link is off-site)
AUDIO AMP + 3KHz FILTER This circuit is the audio amp section for a complete optical transmitter. The circuit amplifies and filters the voice audio signals from an electret microphone. The circuit is described in more detail in the transmitter circuit section of Dave Johnson's Handbook of Optical Through the Air Communications. (this link is off-site)
ELECTRIC FIELD DISTURBANCE MONITOR This schematic is the power supply and front-end sections of the field monitor that is discussed in more detail at Electric Field Disturbance Monitor. The system can detect human and animal motion by the electric fields they disturb.
LOW PASS ACTIVE FILTER DESIGN COLLECTION This is a collection of inverting and non-inverting active low pass filter circuits. I included one, two, three, four and six pole filter circuits. You can change the component value ratios shown, to achieve any frequency cut-off you may need. The circuit does not specify an operational amplifier. The circuits should be used to select the needed resistor and capacitor components for a particular frequency knee and roll-off slope.

Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:

Basic Introduction to Filters: Active, Passive & Switched-Capacitor - National Semiconductor Application Note (app note added 6/06)

Brick-wall lowpass audio filter needs no tuning - 14-Sep-06 Issue of EDN Gyrator supercapacitors eliminate the need for inductors in this 15-kHz filter.... [Design Idea by Diego Puyal and Pilar Molina, University of Zaragoza, Zaragoza, Spain; Edited by Brad Thompson and Fran Granville]

Butterworth Filters - (electronic circuit added 7/03)

Centronics Port D/A converters & low-pass filter - (circuit / schematic design added 6/06)

Chebyshe Volt Bandpass Filter - (electronic circuit added 7/03)

Chebyshe Volt/Butterworth Filters - (electronic circuit added 7/03)

Chopper Amplifiers Complement a DC Accurate Low-Pass Filter - DN9 Design Notes (Linear Technology) (app note added 1/06)

DC Accurate, Active RC Lowpass Filter - Extremely Easy to Use—A Single Resistor Value Sets the Cutoff Frequency (256Hz < fC < 256kHz)…(added 08/08)

Electric Field Disturbance Monitor - This schematic is the power supply and front-end sections of the field monitor that is discussed in more detail at Electric Field Disturbance Monitor. The system can detect human and animal motion by the electric fields they disturb. ….

Filter Akerberg-Mossberg (AM) Second Order Lowpass inverting - Schematic only, no text included

Filter Bach Second Order Lowpass non-inverting - Schematic only, no text included

Filter Berka-Herpy (BH) Second Order Lowpass non-inverting - Schematic only, no text included

Filter First Order Highpass III inverting - Schematic only, no text included

Filter First Order Highpass IV inverting - Schematic only, no text included

Filter First Order Lowpass I non-inverting - Schematic only, no text included

Filter First Order Lowpass II non-inverting - Schematic only, no text included

Filter First Order Lowpass III inverting - Schematic only, no text included

Filter Fliege Second Order Lowpass non-inverting - Schematic only, no text included

Filter KHN (Inverting Input) Second Order Lowpass inverting - Schematic only, no text included

Filter KHN (Non-Inverting Input) Second Order Lowpass non-inverting - Schematic only, no text included

Filter Mikhael-Bhattacharyya (MB) Second Order Lowpass non-inverting - Schematic only, no text included

Filter Multiple Feedback (MFB) Second Order Lowpass I inverting - Schematic only, no text included

Filter Multiple Feedback (MFB) Second Order Lowpass II inverting - Schematic only, no text included

Filter Sallen-Key (SK) Second Order Lowpass I non-inverting - Schematic only, no text included

Filter Sallen-Key (SK) Second Order Lowpass II non-inverting - Schematic only, no text included

Filter Tow-Thomas (TT) Second Order Lowpass non-inverting - Schematic only, no text included

Filter Twin-T Second Order Lowpass non-inverting - Schematic only, no text included

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