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Active Filters: Low Pass
Active Filter -- Main Page
Last Updated on:
Saturday, August 30, 2014 10:27 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:

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.…

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]

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…

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… [Design Idea by Rea Schmid, National Semiconductor, Comlinear Products Group, Fort Collins, CO]

Active-filter circuit and oscilloscope inspect a Class D amplifiers output- 1-Dec-06 Issue of EDN  Ease debugging of bridge-output pulse-width-modulated audio amplifiers with this circuit… [Design Idea 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… [Design Idea by Richard Kurzrok, Queens Village, NY]

Adjustment Free Inclinometer operates on 27V- 4/24/97 EDN-Design Idea  The circuit in Figure 1 is an inclinometer (tilt-measuring circuit] in which the sensor is filled with liquid electrolyte. Acting like a potentiometer, this sensor produces a voltage proportional to the tilt on the center electrode… [Design Idea by John Wettroth, Maxim Integrated Products, Sunnyvale, CA]

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.…

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