Active Filter Circuits
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Last Updated: June 02, 2021 01:44 PM

Broad Band 2Mhz Optical Fiber Receiver -  If you need more sensitivity than the above circuit this circuit provides about ten times more gain.  It too is designed around an inexpensive plastic optical fiber detector. . . Circuit by Dave Johnson P.E.-June, 2000

Broad Band 50Mhz Optical Fiber Receiver Version A -  If the above circuit it still too slow, you can try this circuit.  What it lacks in sensitivity it makes up for in speed.  The circuit attaches a plastic fiber optic PIN photodiode assembly to a small box containing a small 3v battery and a standard . . . Hobby Circuit designed by Dave Johnson P.E.-June, 2000

characteristics of CMOS Logic Inverter Amplifiers -  This chart shows some of the measured characteristics of three different unbuffered CMOS logic gates, used as voltage amplifiers . . . Hobby Circuit designed by Dave Johnson P.E.-February, 2002

CMOS Logic Inverter Amplifier characteristics -  This chart shows some of the measured characteristics of three different unbuffered CMOS logic gates, used as voltage amplifiers. . . Circuit by David Johnson P.E.-February, 2002

Collection Active High Pass Filters -  This is a collection of inverting and non-inverting active high 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 . . . Hobby Circuit designed by David Johnson P.E.-February, 2002

Bandpass filters  -  LC Band pass filters are usually LC filters containing resonator combinations of inductance and capacitance which are designed mathematically to respond to design frequencies while rejecting all other out of band frequencies.  Because LC bandpass filters have inherent limitations these statements should not be taken too literally.   __ Designed by Ian C. Purdie VK2TIP

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

BER meter is easy to build  -  03/02/00 EDN Design Ideas:   General filters are bandpass filters that usually employ bridging couplings between nonadjacent interstage couplings (Reference 1].  This class of filters also includes bridging coupling across  filter input and output ports.  The implementation of input-to-output bridging already exists for a one-pole filter (Reference 2].  For a two-pole filter, dielectric resonators help achieve input-to-output bridging coupling (Reference 3] Design by Luis Miguel Brugarolas, Sire Sistemas y Redes Telmaticas, Tres Cantos, Madrid, Spain

Berka-Herpy (BH) Second Order Bandpass non-Inverting  -  Schematic only, no text included__ 

Berka-Herpy (BH) Second Order Highpass non-Inverting Filter  -  Schematic only, no text included__ 

Biquad Active Bandpass Filter Schematic  -  Schematic only __ Designed by Jim Osburn, WD9EYB

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

Build an Adjustable High-Frequency Notch Filter  -  02/06/03 EDN Design Ideas:  Although you can obtain universal, resistor-programmable switched-capacitor filters that are configurable as notch filters, most cannot operate at bandwidths higher than 100 kHz.  Further, the typically 16- to 20-pin packages do not include a continuous-time, antialiasing filter to prevent spurious signals from appearing at the output Design by John Ambrose, Mixed Signal Integration Corp, San Jose, CA

Butterworth filter has adjustable group Delay  -  08/08/02  EDN Design Ideas:  The Sallen-Key realization of a 5.25-MHz, three-pole Butterworth filter has a gain of 2V/V and can drive 75Ω back-terminated coax with an overall gain of 1 (Figure 1).  Used to reconstruct component-video (Y, Pb, Pr] and RGB signals, t Design by William Stutz, Maxim Integrated Products, Sunnyvale, CA

Cascade bandpass filters for higher Q  -  02/15/00 EDN Design Ideas:  Switched-capacitor filters that are preset for a given bandwidth sometimes do not deliver the bandwidth or Q an application requires.  By inverting the clock between two switched-capacitor bandpass filters, such as the MSFS1 from Mixed Signal integration Corp, you Design by rong Huynh and John Ambrose, Mixed Signal Integration Corp, Santa Clara, CA

CentronICs Port D/A converters & low-pass filter  -  JDAC and CENT_DAC are both simple Digital to Analogue converter to use with your iBM PC/AT or compatible.  Those circuit are connected to Centronics parallel port and does not affect the normal port usage in any way.  The circuits are transparent to computer, so it is not possible to program to see if those devices are connected or not. __ Designed by Tomi Engdahl

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 __ Designed by Milazzo, Carol F., KP4MD

Chebyshev Low pass filter, rolls of at 30MHz  -  This simple 7 element, Chebyshev low pass filter, rolls of at 30MHz.  Attenuation is better than -40dB at 60MHz, -65dB at 90MHz, -80dB at 120MHz. __ Designed by EI9GQ homebrew radio

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/Analog Devices

Clock Tuned, Highly Selective Notch Filter  -  This circuit shows a quick, clean way to tune a notch filter’s center frequency by varying a single resistor, which could be switched.  The LTC1062 switched capacitor filter and A1 form a clock tunable notch (see LTC1062 data sheet).  O1, running from the 5V supply, furnishes the clock, which is level shifted by Q1 to drive the ±5V powered LTC1062.  In this case, three common notch frequencies are listed; others are selectable by tuning O1 in accordance with the equivalency listed__ Linear Technology/Analog Devices App Note, Mar 26th 2010

Closing the loop Deepens notches  -  02/07/02 EDN Design Ideas:  Notch filters remove a single unwanted frequency from an input signal.  They are also a vital component of pulse-shaping networks, such as time-averaging filters.  You can tune a state-variable filter over a wide range by changing the time constants of its integrating amplifiers (references 1, 2, and 3] Design by Tom Napier, North Wales, PA

Collection Active High Pass Filters  -  This is a collection of inverting and non-inverting active high 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 . . . Hobby Circuit designed by David Johnson P.E.-February 11, 2002

Collection of quartz crystal ladder filters  -  in my designs I mostly use 6 pole crystal ladder filters built with standard available quartz crystals.  Since the price of standard available crystal units is relatively low and since the tests show, that 6 quartz crystal are just the right number to effectively and radically filter out the opposite side band in a SSB receiver, I don't see any reason why to built filters with less crystal units. __ Designed by Aleksander Stare

Constant-Impedance IF bandpass filters improve performance  -  Application Note__ MiniCircuits.com

CW Filter-DL7HG  -  Schematic only __ Designed by va3iul

CW Filters  -  Two projects are described here, both of which may be used to enhance simple receivers of the types already described.  These two circuits may be built on the same circuit board and the OP-AMP IC , (LM324) , has sufficient capacity to accomodate both circuits. __ Designed by Harry Lythall-SM0VPO

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

Deliyannis Second Order Bandpass I inverting  -  Schematic only, no text included__ 

Digital signal processor (DSP) for radio communications  -  The W9GR DSP-3 is an improved low cost digital signal processor for radio communications use.   it features 18 DSP functions, a LED display, and 13 bit audio precision__ Quantics

Discrete Component Audio-Frequency RC Filters  -  Many amateur experimenters stay in the familiar comfort zone of HF.  A small number venture into VHF, and even fewer devote time designing, building and operating for the UHF & microwave spectrums.__ 

DPPs program key parameters of bandpass filter  -  12/12/02  EDN Design Ideas:  The three-amplifier implementation of the state-variable filter in Figure 1 provide as for second-order bandpass, highpass, and lowpass responses.  The strength of the circuit, however, is in the bandpass response (VOUT/ViN], in which  Design by Chuck Wojslaw, Catalyst Semiconductor, Sunnyvale, CA

Dynamic Noise Filter  -  Schematic only __ Designed by va3iul

Easy 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

Equal Element Filter Improves Passband Performance  -  12/26/02 EDN Design Ideas:  Designers originally conceived equal-element filters as all-pole microwave bandpass filters that provide minimum center-frequency insertion losses for specific values of resonator-unloaded Q (Reference 1].  All resonators of the equal-element bandpass filter operate at the same loaded Q.  For LC filters, the equal-element filter has another advantage.  In the lowpass prototype Design by Harry Bissell Jr