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Active Filter Circuits
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Last Updated: December 31, 2017 06:46 AM

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

Method of Designing Multiple Order All Pole Bandpass Filters by Cascading 2nd Order Sections  -  AN27A Presents two methods of designing high quality switched capacitor bandpass filters.  Both methods are intended to vastly simplify the mathematics involved in filter design by using tabular methods.  The text assumed no filter design experience but allows high quality filters__ Linear Technology/Analog Devices

Micro-power Band-pass Network  -  Circuit ideas for Designers App Note__ Advanced Linear Devices, Inc

Mikhael-Bhattacharyya (MB) Second Order Bandpass non-Inverting  -  Schematic only, no text included__ 

Mikhael-Bhattacharyya (MB) Second Order Highpass non-Inverting filter  -  Schematic only, no text included__ 

Multi-Function Active Filter Module  -  This versatile Active Filter is ideal for use as an active crossover in loudspeaker systems but has lots of other uses as well.  It can be configured as a low-pass filter (for driving sub-woofer amplifiers) , as a high-pass filter or as a bandpass filter, simply by moving a few on-board jumper links.__ SiliconChip

Multiple Feedback (MFB) Second Order Bandpass II inverting  -  Schematic only, no text included__ 

Multiple Feedback (MFB) Second Order Highpass inverting filter  -  Schematic only, no text included__ 

Multiple Feedback Bandpass Filter  -  The multiple feedback bandpass filter is a simple looking design, but it is difficult to calculate the values for a given set of parameters.  These filters are useful for equalisation, analysis and other tasks such as the Sound to Light converter (Project 62) or even a fully functional Vocoder.  For those who have not heard of the vocoder, it is a device that takes a music source as one input and vocals as the other, allowing a guitar, keyboard or complete ensemble to be made to speak or sing.  The "speech" from a good vocoder is quite intelligible, and is "ear candy" of the very best kind for experimental musicians.   __ Designed by Rod Elliott  ESP

Multiple Feedback Band-pass Filter  -  (spice design)  __ Designed by Rick 

Narrow Band Audio Bandpass Filter  -  This audio bandpass filter is useful for amplification and filtering of weak AM TV video carriers.  For example, a DFM (digital frequency audio multimeter) may have insufficient input sensitivity for measuring extremely weak SSB TV video audio signals.  By using the 20 Hz filter to peak the wanted carrier, the DFM will display the carrier frequency __ Designed by Tony Mann and Todd Emslie

Noise-figure curves ease the selection of low-noise op Amp  -  EDN-Design ideas -- 08/04/1994    Evaluating plots of noise figure vs source resistance makes it easy to select a low-noise amplifier for a given source resistance.  A BASIC  program calculates the numbers from data-sheet parameters.  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, a __ Circuit Design by John W Christensen, National Semiconductor Corp

Notch Filter Autotunes for Audio Applications  -  24-Jun-10 EDN Design Ideas:  Tracking notch filters find use in harmonic-distortion analyzers; they also can remove heterodyne noise from ham-radio systems.  A conventional tracking switched-capacitor notch filter relies on a bandpass filter, a voltage-to-frequency converter, and a notch filter to track the incoming signal and remove undesired tones.  The bandpass filter in these circuits sometimes adjusts to the wrong frequency, meaning that the undesired tone would have no attenuation __ Circuit Design by John R Ambrose, Mixed Signal Integration, San Jose, CA

Notch Filter is DC Accurate  -  03/02/95 EDN Design Ideas:  Most active filters exhibit noise, distortion, gain error, and dc offset.  However, a filter topology that separates the dc and ac paths can eliminate the last two of these unwanted behaviors (Fig 1a).  The dc path in this circuit has no op amps and, therefore, no dc offset.  The dc path does not have a dc gain error other than -6 dB of attenuation that the R1/R2 divider causes. (This attenuation is absent if you omit the R2 termination.) The ac path consists of C1 and a synthetic inductor comprising two wideband transconductance amplifiers and associated components.  The result is an active circuit that emulates the passive filter of Fig 1b __ Circuit Design by Gary Sellani, Maxim Integrated Products, Sunnyvale, CA

Notch Filter Is Insensitive to Component Tolerances  -  03/02/00  EDN Design Ideas:  Many approaches for creating notch filters, which reject a narrow band of frequencies and pass all others, are unsatisfactory because they allow the component tolerances to interact.  The circuit in Figure 1a overcomes this limitation and enables easy calc __ Circuit Design by John Guy, Maxim Integrated Products, Sunnyvale, CA

Notch filter uses only lowpass filter  -  04/10/97 EDN Design Ideas:  Figure 1a shows the textbook method of achieving a notch filter by simply taking the difference of lowpass- and highpass-filter outputs.  However, a real notch need not actually use a highpass filter.  For example, Figure 1b shows how you can create a highpass filter using only a lowpass filter.  This scheme involves subtracting the lowpass filterís output from the input data, and the total frequency response of the system is highpass.    __ Circuit Design by CA Jalaludeen, Defence R&D Organisation, Kochi, Kerala, India

Notebook Power Supply Has Two Output  -  03/03/94 EDN Design Ideas:  The notebook-computer supply in Fig 1 powers the 5V logic and derives an adjustable -24V supply for an LCD's backplane.  The design uses only a high-efficiency buck regulator (Si9150]and an NMOS/PMOS, dual-power-FET chip set (Si9943] __ Circuit Design by Steven C Hageman, Calex Manufacturing Co Inc, Concord, CA

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

Parametric & Graphic Eq's Plus Peaks & Notches  -  if you're into playing with tone controls and notch filters to see how they change the sound out of your effects, you will undoubtedly have built several glops of R's, C's and pots, maybe some L's to make up the tone networks.  While this is fun, it's not very flexible.  Sooner or later you might wonder if there is a more general solution to messing with tone controls.   __ Designed by © 1999 R.G. Keen

Precision level shifter has excellent CMRR  -  15-Apr-04 EDN Design Ideas:  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 high CMRR.  Differential amplifiers contain precision matched internal resistors, so ICs  such as the iNA133 can readily achieve CMRRs of approximately 90 dB __ Circuit Design by Ronald Mancini, Texas Instruments, Bushnell, FL

RC Low-Pass Filter  -  (spice design)  __ Designed by Rick 

RC lowpass filter expands microcomputerís output port  -  06/21/07  EDN Design Ideas:  A simple lowpass RC filter allows a single output pin of a microcontroller to expand the number of output bits __ Circuit Design by Rex Niven, Forty Trout Electronics, Eltham, Victoria, Australia

RC Low-Pass Filter with Op Amp Buffer (single pole filter) with SPICE simulation files  -  Many systems have unwanted signals that can corrupt your signal of interest: digital switching noise, 60 Hz AC power, switching power supply noise, motor drivers, clock oscillators, random noise from resistors and active devices, RF pickup, etc.  For example, imagine you have a 5 kHz signal to be digitized.  Unfortunately, a noise source at 50 kHz has coupled onto your signal.  __ 

RC Notch Filter (Twin T)  -  The twin T notch filter can be used block an unwanted frequency or if placed around an op-amp as a bandpass filter.  The notch frequency occurs where the capacitive reactance equals the resistance Xc=R and if the values are close, the attenuation can be very high and the notch frequency virtually eliminated __ Designed by Bill Bowden

Replace Discrete Lowpass Filters with the LTC1563 Zero Design Effort Two Item Bom & No Surprises  -  DN251 Design Notes__ Linear Technology/Analog Devices

Reverse RIAA Adaptor  -  if youíre short of inputs on your amplifier, but it has an input for a magnetic pickup with RiAA correction, this very simple project will let you convert this into a high-level linear input, making it compatible with the outputs from all current audio sourcesmust register on this site __ Designed by Published in Elecktor July/Aug, 2010

Reverse RIAA Equaliser  -  Test phono preamps for correct equalisation, or convert unused phono inputs.     __ Designed by Rod Elliott  ESP

Active Filter Circuits:   #'s - A     B - E     F - L     M - R     S - Z

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