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Active Filters: Low Pass
Active Filter -- Main Page
Last Updated on:
Tuesday, April 01, 2014 04:28 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. 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)


Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:
"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]
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. .(electronic schematic added 11/08)
1MV Offset Clock-Tunable Monolithic 5-Pole Lowpass Filter -  DN67  Design Notes (Linear Technology) (app note added 6/06)
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. .(electronic schematic added 11/08)
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) . [Designed by David A. Johnson]
8-bit microcontroller implements digital lowpass filter -  24-Jan-08 Issue of EDN  A simple assembler routine fits a digital lowpass filter into a microcontroller.... [Design Idea by Abel Raynus, Armatron International, Malden, MA]
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....(electronic circuit added 7/03)
Active-Filter has Wideband Tuning Range -  03/28/96 EDN-Design Ideas: 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 1s filter section includes a Miller integrator followed by a variable-gain amplifier with overall feedback resistor R2. The overall dc gain is the ratio of R2 to R1.  This circuit has a transfer....[Design Idea added 4/02] [Rea Schmid, National Semiconductor, Comlinear Products Group, Fort Collins, CO] [Design Idea by Rea Schmid, National Semiconductor, Comlinear Products Group, Fort Collins, CO]
Adjustable Filter Provides Lowpass Response -  03/01/01 EDN-Design Ideas  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 discrete-filtering steps by using toggle switches. Manufacturers of commercially available stepped attenuators and adjustable baseband.... [Design Idea 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 the transmitter circuit section of Dave Johnson's Handbook of Optical Through the Air Communications. (this link is off-site) . [Designed by David A. Johnson]

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