passive rc-bandpass with 0dB attenuation in the passband
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From: Mark Freeman on 3 Aug 2010 01:24 Tim Wescott <tim(a)seemywebsite.com> wrote in news:SPednY_R0pRPY8vRnZ2dnUVZ_oednZ2d(a)web-ster.com: > On 08/02/2010 10:12 AM, Jim Thompson wrote: >> On Mon, 2 Aug 2010 10:04:29 -0700 (PDT), cassiope >> <fpm(a)u.washington.edu> wrote: >> >>> passive rc-bandpass filter >> >> Key words: passive rc-bandpass filter... an oxymoron, statement and >> poster :-) > > It depends on how loose your definition is of "bandpass filter". > > > || ___ > Vin o-----||---o--|___|---o-----o Vout > || | | > | | > .-. --- > | | --- > | | | > '-' | > | | > | | > === === > GND GND > (created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de) > > There's a passive RC bandpass filter for you. It's not a _resonant_ > bandpass filter, by any means, but it has a magnitude response that's > zero at f = 0, rises to some maximum, then falls to zero as the > frequency approaches infinity. > LTSpice fans, here are 4 RC's with a peak "gain" of 1.57dB at 113Hz: Version 4 SHEET 1 884 680 WIRE 96 224 -48 224 WIRE 208 224 176 224 WIRE 320 224 208 224 WIRE 208 240 208 224 WIRE -48 320 -48 224 WIRE 96 320 -48 320 WIRE 208 320 208 304 WIRE 208 320 176 320 WIRE -48 336 -48 320 WIRE 208 336 208 320 WIRE -48 432 -48 416 WIRE 208 432 208 400 FLAG -48 432 0 FLAG 208 432 0 FLAG 320 224 Output SYMBOL res 192 208 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R1 SYMATTR Value 10k SYMBOL res 192 304 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R2 SYMATTR Value 1k SYMBOL cap 192 240 R0 SYMATTR InstName C1 SYMATTR Value 0.1� SYMBOL cap 192 336 R0 SYMATTR InstName C2 SYMATTR Value 1� SYMBOL voltage -48 320 R0 WINDOW 123 24 132 Left 0 WINDOW 39 0 0 Left 0 SYMATTR Value2 AC 1 SYMATTR InstName V1 SYMATTR Value SINE(0 1 261) TEXT -24 480 Left 0 !.ac oct 10 10 1k TEXT 256 336 Left 0 ;Voltage Gain > 1\nFrom Epstein, "Synthesis of Passive Networks\nWith Gains Greater than Unity," Proc. IRE,\nJuly 1951 Mark Freeman
From: Mark Freeman on 3 Aug 2010 01:34 Mark Freeman <a4533199(a)bofthew.com> wrote in news:hcKdnUV7nO1sOsrRnZ2dnUVZ_gydnZ2d(a)cablespeedmi.com: > Tim Wescott <tim(a)seemywebsite.com> wrote in > news:SPednY_R0pRPY8vRnZ2dnUVZ_oednZ2d(a)web-ster.com: > >> On 08/02/2010 10:12 AM, Jim Thompson wrote: >>> On Mon, 2 Aug 2010 10:04:29 -0700 (PDT), cassiope >>> <fpm(a)u.washington.edu> wrote: >>> >>>> passive rc-bandpass filter >>> >>> Key words: passive rc-bandpass filter... an oxymoron, statement and >>> poster :-) >> >> >> There's a passive RC bandpass filter for you. It's not a >> >> _resonant_ >> bandpass filter, by any means, but it has a magnitude response that's >> zero at f = 0, rises to some maximum, then falls to zero as the >> frequency approaches infinity. >> > > LTSpice fans, here are 4 RC's with a peak "gain" of 1.57dB at 113Hz: > > Mark Freeman Excuse me, I meant 1.157dB. Mark Freeman
From: nukeymusic on 3 Aug 2010 04:04 On Aug 2, 10:35 pm, Tim Wescott <t...(a)seemywebsite.com> wrote: > On 08/02/2010 01:06 PM, nukeymusic wrote: > > > On Aug 2, 7:04 pm, cassiope<f...(a)u.washington.edu> wrote: > >> On Aug 2, 7:50 am, nukeymusic<nukeymu...(a)gmail.com> wrote: > > >>> Is it possible to make a passive rc-bandpass filter which has 0dB > >>> attenuation in the passband with only 4 components? > > >>> nukey > > >> How close to 0dB? What sort of Q (bw/f0)? What's the load? > > > exactly 0dB, unloaded, Q to be determined from the other specifications > > Q is almost meaningless in this case -- >any passive RC bandpass filter > is going to have a damping ratio greater than 1, and the various > definitions of Q only converge for damping ratios much less than one. > can you prove this or refer to a proof of this statement? thanks in advance nukey > -- > > Tim Wescott > Wescott Design Serviceshttp://www.wescottdesign.com > > Do you need to implement control loops in software? > "Applied Control Theory for Embedded Systems" was written for you. > See details athttp://www.wescottdesign.com/actfes/actfes.html
From: nukeymusic on 3 Aug 2010 04:14 On Aug 3, 7:24 am, Mark Freeman <a4533...(a)bofthew.com> wrote: > Tim Wescott <t...(a)seemywebsite.com> wrote innews:SPednY_R0pRPY8vRnZ2dnUVZ_oednZ2d(a)web-ster.com: > > > > > On 08/02/2010 10:12 AM, Jim Thompson wrote: > >> On Mon, 2 Aug 2010 10:04:29 -0700 (PDT), cassiope > >> <f...(a)u.washington.edu> wrote: > > >>> passive rc-bandpass filter > > >> Key words: passive rc-bandpass filter... an oxymoron, statement and > >> poster :-) > > > It depends on how loose your definition is of "bandpass filter". > > > || ___ > > Vin o-----||---o--|___|---o-----o Vout > > || | | > > | | > > .-. --- > > | | --- > > | | | > > '-' | > > | | > > | | > > === === > > GND GND > > (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de) > > > There's a passive RC bandpass filter for you. It's not a _resonant_ > > bandpass filter, by any means, but it has a magnitude response that's > > zero at f = 0, rises to some maximum, then falls to zero as the > > frequency approaches infinity. > > LTSpice fans, here are 4 RC's with a peak "gain" of 1.57dB at 113Hz: > > Version 4 > SHEET 1 884 680 > WIRE 96 224 -48 224 > WIRE 208 224 176 224 > WIRE 320 224 208 224 > WIRE 208 240 208 224 > WIRE -48 320 -48 224 > WIRE 96 320 -48 320 > WIRE 208 320 208 304 > WIRE 208 320 176 320 > WIRE -48 336 -48 320 > WIRE 208 336 208 320 > WIRE -48 432 -48 416 > WIRE 208 432 208 400 > FLAG -48 432 0 > FLAG 208 432 0 > FLAG 320 224 Output > SYMBOL res 192 208 R90 > WINDOW 0 0 56 VBottom 0 > WINDOW 3 32 56 VTop 0 > SYMATTR InstName R1 > SYMATTR Value 10k > SYMBOL res 192 304 R90 > WINDOW 0 0 56 VBottom 0 > WINDOW 3 32 56 VTop 0 > SYMATTR InstName R2 > SYMATTR Value 1k > SYMBOL cap 192 240 R0 > SYMATTR InstName C1 > SYMATTR Value 0.1µ > SYMBOL cap 192 336 R0 > SYMATTR InstName C2 > SYMATTR Value 1µ > SYMBOL voltage -48 320 R0 > WINDOW 123 24 132 Left 0 > WINDOW 39 0 0 Left 0 > SYMATTR Value2 AC 1 > SYMATTR InstName V1 > SYMATTR Value SINE(0 1 261) > TEXT -24 480 Left 0 !.ac oct 10 10 1k > TEXT 256 336 Left 0 ;Voltage Gain > 1\nFrom Epstein, "Synthesis of > Passive Networks\nWith Gains Greater than Unity," Proc. IRE,\nJuly 1951 > > Mark Freeman That's the low pass version of the delayed-recovery filter patented by G.A. Philbrick, I wouldn't call this a bandpass filter Do you think this can be transformed into a bandpass-filter? (you will probably end with more than 4 components?) thanks for sharing your time nukey
From: cassiope on 3 Aug 2010 13:23
On Aug 2, 1:35 pm, Tim Wescott <t...(a)seemywebsite.com> wrote: > On 08/02/2010 01:06 PM, nukeymusic wrote: > > > On Aug 2, 7:04 pm, cassiope<f...(a)u.washington.edu> wrote: > >> On Aug 2, 7:50 am, nukeymusic<nukeymu...(a)gmail.com> wrote: > > >>> Is it possible to make a passive rc-bandpass filter which has 0dB > >>> attenuation in the passband with only 4 components? > > >>> nukey > > >> How close to 0dB? What sort of Q (bw/f0)? What's the load? > > > exactly 0dB, unloaded, Q to be determined from the other specifications > > Q is almost meaningless in this case -- any passive RC bandpass filter > is going to have a damping ratio greater than 1, and the various > definitions of Q only converge for damping ratios much less than one. > > -- > > Tim Wescott > Wescott Design Serviceshttp://www.wescottdesign.com > > Do you need to implement control loops in software? > "Applied Control Theory for Embedded Systems" was written for you. > See details athttp://www.wescottdesign.com/actfes/actfes.html Ok, so I have used a more generalized definition of Q (bw/f0). Fortunately, definitions rarely have convergence problems. Applying them in specific instances is another matter ;) The simpleminded 4-component RC filter (the obvious serial-parallel arrangement) won't get to exactly 0dB... would only approach it for truly wide bandwidths, even with no load. |