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Active Filters: Low Pass
Active Filter -- Main Page
Last Updated on:
Tuesday, May 19, 2015 05:28 AM

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 . . . [Circuit by Dave Johnson P.E.,  06/04/00]

  • Active Low Pass Filter Designs  -  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 . . . [Circuit by David Johnson P.E.,  12/10/00]

  • 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 . . . [Circuit by David A. Johnson P.E.,  06/04/00]

  • Low Pass Active Filter Designs  -  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 . . . [Circuit by David A. Johnson P.E.,  12/10/00]


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

1 Resistor Tunes Lowpass Filter -  08/21/03  EDN Design Idea   Any tunable, second-order, active RC-filter section requires at least two thoroughly matched variable resistors. But the lowpass implementation in Figure 1 provides for wide-range cutoff-frequency control using only a single variab… [by Vladimir Tepin, State Radioengineering University, Taganrog, Russia]

 

1.8V, 140uA, 100kHz, Lowpass Filter (Single-Ended Input and Differential Output) -  The LTC6256 circuit shown here is a 2nd order, 100kHz, Butterworth lowpass filter. The filter’s differential output maximizes the dynamic range in very low voltage operation. The LTC6255/LTC6256/LTC6257 are single/dual/quad operational amplifiers with low noise, low power, low supply voltage, rail-to-rail input/output… [Linear Technology App Note, Jul 20th 2010

 

19 kHz MPX Low Pass Filter -  This map, armored also enables automatic MONO / MPX through a low-pass filter, even with a multiplex on its entry by using an ON / ON, panning, the whole spectrum MPX more RDS is sent to the synthesizer, on the other hand when it is in a position MONO, the low-pass filter is activated and share its cutoff frequency at 15 KHz, only modulation G + D is sent to the synthesizer, as 19 KHz. 19 KHz carrier, the signal multiplex and subcarrier 57 KHz is thereby eliminated, which provides ease of use for example in a string of issue relay tuner, if the link between the issuer Departure and receiver re-issue was not of good quality stereo, you sufficient to switch to mono to improve sound quality, you can then connect the RDS encoder at the re-issuer.…

 

20 kHz MPX Low Pass Filter -  This map, armored also enables automatic MONO / MPX through a low-pass filter, even with a multiplex on its entry by using an ON / ON, panning, the whole spectrum MPX more RDS is sent to the synthesizer, on the other hand when it is in a position MONO, the low-pass filter is activated and share its cutoff frequency at 15 KHz, only modulation G + D is sent to the synthesizer, as 19 KHz. 19 KHz carrier, the signal multiplex and subcarrier 57 KHz is thereby eliminated, which provides ease of use for example in a string of issue relay tuner, if the link between the issuer Departure and receiver re-issue was not of good quality stereo, you sufficient to switch to mono to improve sound quality, you can then connect the RDS encoder at the re-issuer.… [Designer's name not included]

 

20 kHz MPX Low Pass Filter -  Cette carte, blindée elle aussi, permet la commutation automatique MONO/MPX grâce à un filtre passe-bas, même avec une source multiplex sur son entrée, par l'utilisation d'un interrupteur ON/ON. En position stéréo, tout le spectre MPX plus RDS est envoyé au synthétiseur. Par contre, lorsque celui-ci est en position MONO, le filtre passe-bas est activé, et de par sa fréquence de coupure à 15 KHz, seule la modulation G + D est envoyée au synthé.… [Designer's name not included]

 

3Khz Filter + Audio Amplifier -  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 . . . [Hobby Circuit designed by Dave Johnson P.E.,  06/04/00]

 

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 . . . [Circuit by Dave Johnson P.E.,  06/04/00]

 

3rd Order Filter-Using Model 425  -  No description, just schematic - OpAmps Lab Inc is the manufactor ofAmplifiers (Video / Audio / Distribution / Microphone / Equalization / Line / VCA / Power), Switchers (Routing / Assign / Matrix), Mult (Press) (Network-Feed) Boxes, Audio Transformers, Oscillators, Power-Supplies, Custom Sub-Systems. … [Application OpAmps Lab Inc.]

 

440 Hertz Peaked Low Pass Audio Filter Experiments -  At audio frequencies, low pass filtering can go a long way to improving CW and beacon reception. It has a been a long time since I built one and therefore decided to experiment with some designs using the 5532 op amp… [Todd, VE7BPO]

 

8-Bit Microcontroller Implements Digital Lowpass Filter -  01/24/08  EDN Design Idea   A simple assembler routine fits a digital lowpass filter into a microcontroller… [by Abel Raynus, Armatron International, Malden, MA]

 

A Differential Input-to-Single-Ended Output Amplifier -  This circuit shows a circuit for converting a differential input to a single-ended output. For a gain equal to one (R1 = R2 = 604W and VOUT = V2 – V1) the input referred differential voltage noise density is 9nV/rtHz and differential input signal-to-noise ratio is 80.9dB with 0.2VRMS input signal in a 4MHz noise bandwidth.… [Linear Technology App Note, Jul 2, 2012]

 

A Single-Ended Input to Differential Output Amplifier -  This circuit shows a circuit for generating a differential signal from a single-ended input. The differential output noise is a function of the noise of the amplifiers, the noise of resistors R1 and R2 and the noise bandwidth. For example, if R1 and R2 are each 200W, the differential output voltage noise density is 9.5 nV/ÖHz… [Linear Technology App Note, Jul 2, 2012]

 

Active 2nd Order Filters -  The figures below illustrate using opamps as active 2nd order filters. Three 2nd order filters are shown, low pass, high pass, and bandpass. Each of these filters will attenuate frequencies outside their passband at a rate of 12dB per octave or 1/4 the voltage amplitude for each octave of frequency increase or decrease outside the passband… [Bill Bowden, designer]

 

Active Filter Has Wideband Tuning Range -  03/28/96 EDN Design Idea   . You can use the basic building block of Figure 1and high-speed analog components to build a second-order lowpass variable-frequency filter with excellent phase linearity (Figure 2]. Figure 1’s filter section includes a Miller in… [by Rea Schmid, National Semiconductor, Comlinear Products Group, Fort Collins, CO]

 

Active Low Pass Filter Designs -  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 . . . [Circuit by David Johnson P.E.,  12/10/00]

 

Active-filter circuit and oscilloscope inspect a Class D amplifiers output -  12/01/06  EDN Design Idea   Ease debugging of bridge-output pulse-width-modulated audio amplifiers with this circuit… [by John Guy, Maxim Integrated Products Inc, Sunnyvale, CA]

 

Adjustable filter provides lowpass response -  03/01/01 EDN Design Idea   You can configure simple lowpass filters as pi sections with nominal three-pole, 0.1-dB Chebyshev response to provide a moderate amount of stopband selectivity. You can put four of these filters into one enclosure and then select… [by Richard Kurzrok, Queens Village, NY]

 

Applications for a DC Accurate Lowpass Switched-Capacitor Filter -  AN20 Linear Technology Discusses  principles of operation of  LTC1062 and helpful hints for its application. Various application circuits are explained in detail with focus on how to cascade two LTC1062s and how to obtain notches. Noise and distortion performance are fully illustrated.…

 

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 . . . [Circuit by David A. Johnson P.E.,  06/04/00]

 

 

 

Basic Introduction to Filters: Active, Passive & Switched-Capacitor -  National Semiconductor Application Note…

 

Brick-wall lowpass audio filter needs no tuning -  09/14/06  EDN Design Idea   Gyrator supercapacitors eliminate the need for inductors in this 15-kHz filter… [by Diego Puyal and Pilar Molina, University of Zaragoza, Zaragoza, Spain]

 

Butterworth Filters -  …

 

Centronics Port D/A converters & low-pass filter -  … [Designed by Tomi Engdahl]

 

Chebyshev Bandpass Filter -  …

 

Chebyshev/Butterworth Filters -  This program was written in PC-BASIC for automated design of Chebyshev and Butterworth filters in the low-pass, high-pass, band-pass and band-stop configurations. These filters are composed of a series of circuit branches which are alternately connected in series or shunt with the source-to-load path. In low-pass and high-pass filters, each branch is either a capacitor or an inductor. In band-pass and band-stop filters…

 

Chopper Amplifiers Complement a DC Accurate Low-Pass Filter -  DN9  Design Notes (Linear Technology)…

 

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

 

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 quashes 60-Hz interference -  03/21/13  EDN Design Idea   9Originally published in the December 19, 1991, issue of EDN)   The circuit in Figure 1 filters 60-Hz interference from low-frequency, low-level signals. The filter exhibits 40-dB rejection (Q=0.75) and draws 95 μA max from a single-sided 5V supply.… [by Adolfo Garcia]

 

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…

 

 

 

Generate CID/CIDCW Analog Signals -  12/07/00 EDN Design Idea   A high-speed mP and active lowpass filters can generate CID (caller-ID]and CIDCW (caller-ID-on-callwaiting] analog signals (Figure 1). CID data transmits at 1200 baud FSK between the first and second 20-Hz ring of an incoming call. … [by Hans Krobath, EEC, Nesconset, NY]

 

High Linearity Components Simplify Direct Conversion Receiver Designs -  LT5575 Demodulator with 20MHz Low pass Filter, common mode output voltage can be set regardless of input voltage. A filter at the output of the demodulator filters out of band signal and the filter at the inputs of the ADC performs the anti aliasing function.… [Linear Technology App Note, Jul 2, 2012]

 

Improve roll-off of Sallen-Key filter -  09/30/04 EDN Design Idea   The well-documented Sallen-Key active filter is a staple of analog design.This Design Idea shows a way to obtain better roll-off by adding just a few common passive components.Figure 1aPage includes several designs.Scroll t… [by Doug Glenn, Teledyne, Lewisburg, TN]

 

Low Pass Active Filter -  …

 

Low Pass Active Filter Designs -  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 . . . [Circuit by David A. Johnson P.E.,  12/10/00]

 

Low Pass Filter for FM 88-108 MHz -  Filter used for eliminate unwanted harmonic frequency at second and third. Notch filter, Band Pass Filter (BPF) , and High Pass Filter (HPF) sometime combined in constructing LPF design. Schematic below for FM Broadcast Lowpass Filter 88-108 MHz…

 

Low Pass Filter, 3Khz, With An 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 . . . [Hobby Circuit designed by David A. Johnson P.E.,  06/04/00]

 

Low pass filter-subwoofer filter -  The acoustic spectrum is extended by very low frequencies 20Iz and reaches as the 20000Iz in high frequencies. In the low frequencies is degraded the sense of direction. This reason us leads to the utilization speaker for the attribution of very low frequencies. The manufacture that to you we propose distinguishes these frequencies, in order to him we lead to the corresponding amplifier. The acoustic filters are met in various points in the sound systems.… [Steve Filianos]

 

Lowpass Filter Discriminates Step Input from Noise -  09/18/03  EDN Design Idea   Numerous applications exist in industry, particularly with control systems, in which it is desirable to remove all but the lowest frequency components from a signal to effectively yield a dc voltage.This voltage may, for example,… [by Eric Desrochers, Aircuity Inc, Newton, MA]

 

Low-Pass Filter RFI Filter -  Circuit Ideas for Designers App Note… [Advanced Linear Devices, Inc]

 

Low-Sensitivity, Lowpass Filter Design -  National Semiconductor Application Note  …

 

LPF -  HF Low Pass Filter… [EI9GQ homebrew radio]

 

LTC1560-1: Tiny 1MHz Lowpass Filter uses No Inductors -  DN169  Design Notes (Linear Technology)…

 

Noise-figure curves ease the selection of low-noise op amp -  08/04/94  EDN Design Idea   Selecting the right op amp can be a serious challenge when you take all of the possible parameters into consideration. Choosing a low- noise amplifier is particularly daunting. Both internal and external sources of noise, including many that designers ignore or don't recognize, affect the op amp's and overall system's noise performance. Different types of op amps—CMOS, JFET, and bipolar—exhibit various noise characteristics about which you can make some dangerous generalizations. However, an important tool, namely using low noise figure (NF) for given source resistance, does exist to help take some of the guesswork out of choosing a low-noise amplifier.… [by John W Christensen, National Semiconductor Corp]

 

OA-27: OA-27 Low-Sensitivity, Lowpass Filter Design -  National Semiconductor Application Note  …

 

One Resistor Tunes Lowpass Filter -  08/21/03  EDN Design Idea   Any tunable, second-order, active RC-filter section requires at least two thoroughly matched variable resistors. But the lowpass implementation in Figure 1 provides for wide-range cutoff-frequency control using only a single variab… [by Vladimir Tepin, State Radioengineering University, Taganrog, Russia]

 

Precision level shifter has excellent CMRR -  04/15/04  EDN Design Idea   Most designers make level shifters with op amps and 1%-tolerance discrete resistors. Discrete-resistor mismatching limits the op amp's CMMR (common-mode rejection ratio] to 40 dB, so you cannot use op amps in circuits that require h… [by Ronald Mancini, Texas Instruments, Bushnell, FL]

 

 

 

RC Low-Pass Filter -  (spice design) … [Rick (last name not given)]

 

RC lowpass filter expands microcomputer’s output port -  06/21/07  EDN Design Idea   A simple lowpass RC filter allows a single output pin of a microcontroller to expand the number of output bits… [by Rex Niven, Forty Trout Electronics, Eltham, Victoria, Australia]

 

Replace Discrete Lowpass Filters with the LTC1563 Zero Design Effort Two Item Bom & No Surprises -  DN251  Design Notes (Linear Technology)…

 

Sallen-Key Low-Pass Filter -  (spice design) … [Rick (last name not given)]

 

Single 2.7V Supply 4MHz 4th Order Lowpass Butterworth Filter -  Benefiting from low voltage operation and rail-to-rail output, a low power filter that is suitable for antialiasing can be built as shown in this circuit. On a 2.7V supply the filter has a passband of approximately 4MHz with 2VP-P input signal and a stopband attenuation that is greater than –75dB at 43MHz. The resistor and… [Linear Technology App Note, Jul 20th 2010]

 

Single Resistor Tunes Lowpass Filter -  08/21/03  EDN Design Idea   Any tunable, second-order, active RC-filter section requires at least two thoroughly matched variable resistors. But the lowpass implementation in Figure 1 provides for wide-range cutoff-frequency control using only a single variab… [by Vladimir Tepin, State Radioengineering University, Taganrog, Russia]

 

Single Supply 10MHz Lowpass Filter Features the LT1819 Op Amp and Adjustable Bandwidth Up to 20MHz -  Low noise, low distortion LT1819 circuit trades parts count and components sensitivity for an adjustable bandwidth - up to 20MHz Diff in diff out circuit. Measured signal-to-noise plus distortion for LT1819 circuit is 71.5dB, just a little nosier than the fixed bandwidth LT6600-10 filter differential filter.… [ Linear Technology App Note, Jul 2, 2012]

 

Single Supply, Micropower, Second Order Lowpass Filter with 60Hz Notch -  The first section is a standard low-pass filter with Fc=40Hz. The second section is a notch filter tuned to eliminate 60Hz mains pickup from the signal.… [Linear Technology App Note, Jun 21, 2011]

 

Sixth-Order Butterworth Low-Pass Filter -  Low-pass filters are widely used in the audio domain. Their most important application is in communication receivers and communication audio circuitry. These filters, when used for audio communications, start attenuating frequencies above 3.4 kHz, as the bandwidth of the human voice (as far as voice clarity and intelligibility are concerned) is 300 Hz to 3.4 kHz. … [© EFY Enterprises Pvt. Ltd. All rights reserved.]

 

Source resistance and noise considerations in amplifiers -  This application note demonstrates how a CMOS amplifier is the best choice when a high source resistance is used and noise is the only concern.… [Application Note -- 05.01.2012]

 

SSB AF Filter -  This is a simple filter that restricts the LF response a little as well providing quite a heavy HF roll-off. The prototype has enhanced a Yaesu FT101B that was only fitted with an AM IF filter. The IC is an LM358.… [from Harry Lythall's website]

 

Unique Applications for the LTC1062 Lowpass Filter -  AN24 Linear Technology Highlights the LTC1062 as a lowpass filter in a phase lock loop. Describes how the loop's bandwidth can be increased and the VCO output jitter reduced when the LTC1062 is the loop filter. Compares it with a passive RC loop filter. Also discussed is the use of LTC1062 as simple bandpass and band stop filter.…

 

Wideband filter uses image parameters -  10/26/00  EDN Design Idea   You can design various lowpass and highpass filters using image parameters ( Reference 1 and Reference 2 ]. By cascading a highpass and a lowpass filter.PDF has several circuits, please scroll to find this one.… [by Richard M Kurzrok, RMK Consultants, Queens Village, NY]


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