passive rc-bandpass with 0dB attenuation in the passband

Started by nukeymusic August 2, 2010
Is it possible to make a passive rc-bandpass filter which has 0dB
attenuation in the passband with only 4 components?

nukey
On Aug 2, 7:50 am, nukeymusic <nukeymu...@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?
On Mon, 2 Aug 2010 10:04:29 -0700 (PDT), cassiope
<fpm@u.washington.edu> wrote:

>passive rc-bandpass filter
Key words: passive rc-bandpass filter... an oxymoron, statement and poster :-) ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Postings via gmail, yahoo, hotmail, aioe, uar or googlegroups, and trolls/feeders, are now automatically kill-filed using Agent v6.0 To be white-listed, send request via the E-mail icon on my website
On 08/02/2010 10:12 AM, Jim Thompson wrote:
> On Mon, 2 Aug 2010 10:04:29 -0700 (PDT), cassiope > <fpm@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. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html
On 08/02/2010 07:50 AM, nukeymusic wrote:
> Is it possible to make a passive rc-bandpass filter which has 0dB > attenuation in the passband with only 4 components?
Ask your prof? Review your class notes? There's some passive RC filter with not too many components that actually has a bit of voltage gain. It's usefulness is pretty much limited to winning bets in University bars, but it's out there. I can't even remember if it's bandpass, but if it isn't it may have a bandpass cousin. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html
On Aug 2, 7:50 am, nukeymusic <nukeymu...@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
Can I buy a vowel? Er, make that an inductor....
On Aug 2, 7:04 pm, cassiope <f...@u.washington.edu> wrote:
> On Aug 2, 7:50 am, nukeymusic <nukeymu...@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
This configuration won't give 0dB in the passband

On Aug 2, 7:21 pm, Tim Wescott <t...@seemywebsite.com> wrote:
> On 08/02/2010 10:12 AM, Jim Thompson wrote: > > > On Mon, 2 Aug 2010 10:04:29 -0700 (PDT), cassiope > > <f...@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. > > -- > > 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
On Aug 2, 9:54 pm, "m...@sushi.com" <m...@sushi.com> wrote:
> On Aug 2, 7:50 am, nukeymusic <nukeymu...@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 > > Can I buy a vowel? Er, make that an inductor....
no inductors allowed here
On 08/02/2010 01:06 PM, nukeymusic wrote:
> On Aug 2, 7:04 pm, cassiope<f...@u.washington.edu> wrote: >> On Aug 2, 7:50 am, nukeymusic<nukeymu...@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 Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html
On Tue, 3 Aug 2010 01:14:44 -0700 (PDT), nukeymusic
<nukeymusic@gmail.com> wrote:

>On Aug 3, 7:24 am, Mark Freeman <a4533...@bofthew.com> wrote: >> Tim Wescott <t...@seemywebsite.com> wrote innews:SPednY_R0pRPY8vRnZ2dnUVZ_oednZ2d@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...@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
So you are just a troll.
On 08/04/2010 10:32 AM, cassiope wrote:
> On Aug 4, 2:20 am, nukeymusic<nukeymu...@gmail.com> wrote: >> On Aug 3, 8:54 pm, Tim Wescott<t...@seemywebsite.com> wrote: >> >> >> >>> On 08/03/2010 11:19 AM, Jim Thompson wrote: >> >>>> On Tue, 03 Aug 2010 10:35:41 -0700, Tim Wescott<t...@seemywebsite.com> >>>> wrote: >> >>>>> On 08/03/2010 10:23 AM, cassiope wrote: >>>>>> On Aug 2, 1:35 pm, Tim Wescott<t...@seemywebsite.com> wrote: >>>>>>> On 08/02/2010 01:06 PM, nukeymusic wrote: >> >>>>>>>> On Aug 2, 7:04 pm, cassiope<f...@u.washington.edu> wrote: >>>>>>>>> On Aug 2, 7:50 am, nukeymusic<nukeymu...@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. >> >>>>> Yes, I cited that circuit to contradict Jim's statement that "you can't >>>>> make a passive RC bandpass circuit", not to answer the OP's question. >> >>>> With horrible skirts. "Band-pass" usually implies skirt-rate relative >>>> to bandwidth. >> >>> Yes. It's more of a "scholar's bandpass" than anything you might want >>> to use in real life. It's not a bad mental tool to use when cooking up >>> an active filter, because an active bandpass can be made by "sharpening >>> up" a passive one, ditto with an active lowpass and (with due respect >>> for stability) an active highpass. >> >>> -- >> >>> 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 >> >> Dear Tim, >> You probably did not see my question in the other message, therefore >> I'd like to ask it here once more: >> Can you prove the following statement or point to a proof for it: >> >> any passive RC bandpass filter is going to have a damping ratio >> greater than 1, >> >> regards, >> nukey > > While the standard form of a twin-T filter isn't a band-pass, it's a > band-reject, it can have a very high Q. > I'm (almost) sure some clever person can find the right combination of > terminals to yield a bandpass. > Now if you limit your design to ladder networks, the proof might be > possible. I have a vague recollection > of a proof that you can't have coincident poles in a passive RC ladder > network (but I could be wrong about that, > it's been a long time...).
It can have a very deep null, but as a passive network it isn't resonant. If you want a twin-T notch filter to be resonant then you need to use it as part of an active filter. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html
On Aug 4, 2:20 am, nukeymusic <nukeymu...@gmail.com> wrote:
> On Aug 3, 8:54 pm, Tim Wescott <t...@seemywebsite.com> wrote: > > > > > On 08/03/2010 11:19 AM, Jim Thompson wrote: > > > > On Tue, 03 Aug 2010 10:35:41 -0700, Tim Wescott<t...@seemywebsite.com> > > > wrote: > > > >> On 08/03/2010 10:23 AM, cassiope wrote: > > >>> On Aug 2, 1:35 pm, Tim Wescott<t...@seemywebsite.com>   wrote: > > >>>> On 08/02/2010 01:06 PM, nukeymusic wrote: > > > >>>>> On Aug 2, 7:04 pm, cassiope<f...@u.washington.edu>     wrote: > > >>>>>> On Aug 2, 7:50 am, nukeymusic<nukeymu...@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. > > > >> Yes, I cited that circuit to contradict Jim's statement that "you can't > > >> make a passive RC bandpass circuit", not to answer the OP's question. > > > > With horrible skirts.  "Band-pass" usually implies skirt-rate relative > > > to bandwidth. > > > Yes.  It's more of a "scholar's bandpass" than anything you might want > > to use in real life.  It's not a bad mental tool to use when cooking up > > an active filter, because an active bandpass can be made by "sharpening > > up" a passive one, ditto with an active lowpass and (with due respect > > for stability) an active highpass. > > > -- > > > 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 > > Dear Tim, > You probably did not see my question in the other message, therefore > I'd like to ask it here once more: > Can you prove the following statement or point to a proof for it: > > any passive RC bandpass filter is going to have a damping ratio > greater than 1, > > regards, > nukey
While the standard form of a twin-T filter isn't a band-pass, it's a band-reject, it can have a very high Q. I'm (almost) sure some clever person can find the right combination of terminals to yield a bandpass. Now if you limit your design to ladder networks, the proof might be possible. I have a vague recollection of a proof that you can't have coincident poles in a passive RC ladder network (but I could be wrong about that, it's been a long time...).
On 08/04/2010 02:20 AM, nukeymusic wrote:
> On Aug 3, 8:54 pm, Tim Wescott<t...@seemywebsite.com> wrote: >> On 08/03/2010 11:19 AM, Jim Thompson wrote: >> >> >> >>> On Tue, 03 Aug 2010 10:35:41 -0700, Tim Wescott<t...@seemywebsite.com> >>> wrote: >> >>>> On 08/03/2010 10:23 AM, cassiope wrote: >>>>> On Aug 2, 1:35 pm, Tim Wescott<t...@seemywebsite.com> wrote: >>>>>> On 08/02/2010 01:06 PM, nukeymusic wrote: >> >>>>>>> On Aug 2, 7:04 pm, cassiope<f...@u.washington.edu> wrote: >>>>>>>> On Aug 2, 7:50 am, nukeymusic<nukeymu...@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. >> >>>> Yes, I cited that circuit to contradict Jim's statement that "you can't >>>> make a passive RC bandpass circuit", not to answer the OP's question. >> >>> With horrible skirts. "Band-pass" usually implies skirt-rate relative >>> to bandwidth. >> >> Yes. It's more of a "scholar's bandpass" than anything you might want >> to use in real life. It's not a bad mental tool to use when cooking up >> an active filter, because an active bandpass can be made by "sharpening >> up" a passive one, ditto with an active lowpass and (with due respect >> for stability) an active highpass. >> >> -- >> >> 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 > > Dear Tim, > You probably did not see my question in the other message, therefore > I'd like to ask it here once more: > Can you prove the following statement or point to a proof for it: > > any passive RC bandpass filter is going to have a damping ratio > greater than 1,
No, I can't. I'm not sure if that was ever even proved to me -- it's just one of those "obvious truths" that get presented early in one's educational career, and is never questioned thereafter. I'm certain that it _is_ true -- if it weren't I'd have seen a circuit that took advantage of a resonant RC network. Further, I'm certain that some clever network theorist has proved it. I just don't know where to look for such a proof. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html
On Aug 3, 8:54 pm, Tim Wescott <t...@seemywebsite.com> wrote:
> On 08/03/2010 11:19 AM, Jim Thompson wrote: > > > > > On Tue, 03 Aug 2010 10:35:41 -0700, Tim Wescott<t...@seemywebsite.com> > > wrote: > > >> On 08/03/2010 10:23 AM, cassiope wrote: > >>> On Aug 2, 1:35 pm, Tim Wescott<t...@seemywebsite.com>   wrote: > >>>> On 08/02/2010 01:06 PM, nukeymusic wrote: > > >>>>> On Aug 2, 7:04 pm, cassiope<f...@u.washington.edu>     wrote: > >>>>>> On Aug 2, 7:50 am, nukeymusic<nukeymu...@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. > > >> Yes, I cited that circuit to contradict Jim's statement that "you can't > >> make a passive RC bandpass circuit", not to answer the OP's question. > > > With horrible skirts.  "Band-pass" usually implies skirt-rate relative > > to bandwidth. > > Yes.  It's more of a "scholar's bandpass" than anything you might want > to use in real life.  It's not a bad mental tool to use when cooking up > an active filter, because an active bandpass can be made by "sharpening > up" a passive one, ditto with an active lowpass and (with due respect > for stability) an active highpass. > > -- > > 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
Dear Tim, You probably did not see my question in the other message, therefore I'd like to ask it here once more: Can you prove the following statement or point to a proof for it: any passive RC bandpass filter is going to have a damping ratio greater than 1, regards, nukey
On 08/03/2010 11:19 AM, Jim Thompson wrote:
> On Tue, 03 Aug 2010 10:35:41 -0700, Tim Wescott<tim@seemywebsite.com> > wrote: > >> On 08/03/2010 10:23 AM, cassiope wrote: >>> On Aug 2, 1:35 pm, Tim Wescott<t...@seemywebsite.com> wrote: >>>> On 08/02/2010 01:06 PM, nukeymusic wrote: >>>> >>>>> On Aug 2, 7:04 pm, cassiope<f...@u.washington.edu> wrote: >>>>>> On Aug 2, 7:50 am, nukeymusic<nukeymu...@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. >> >> Yes, I cited that circuit to contradict Jim's statement that "you can't >> make a passive RC bandpass circuit", not to answer the OP's question. > > With horrible skirts. "Band-pass" usually implies skirt-rate relative > to bandwidth.
Yes. It's more of a "scholar's bandpass" than anything you might want to use in real life. It's not a bad mental tool to use when cooking up an active filter, because an active bandpass can be made by "sharpening up" a passive one, ditto with an active lowpass and (with due respect for stability) an active highpass. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html
On Tue, 03 Aug 2010 10:35:41 -0700, Tim Wescott <tim@seemywebsite.com>
wrote:

>On 08/03/2010 10:23 AM, cassiope wrote: >> On Aug 2, 1:35 pm, Tim Wescott<t...@seemywebsite.com> wrote: >>> On 08/02/2010 01:06 PM, nukeymusic wrote: >>> >>>> On Aug 2, 7:04 pm, cassiope<f...@u.washington.edu> wrote: >>>>> On Aug 2, 7:50 am, nukeymusic<nukeymu...@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. > >Yes, I cited that circuit to contradict Jim's statement that "you can't >make a passive RC bandpass circuit", not to answer the OP's question.
With horrible skirts. "Band-pass" usually implies skirt-rate relative to bandwidth.
> >As I told the OP, I do dimly remember a passive RC circuit that had >voltage (but certainly not power!) gain at some frequency. But I don't >think it was a bandpass, and I don't know if one could build a bandpass >version of it. If you could design a bandpass, passive, RC circuit with >gain, then it would be a snap to design one with a 0dB peak. Realizing >exactly a 0dB peak with component tolerances and all would be more of a >trick, I'm sure.
...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Spice is like a sports car... Performance only as good as the person behind the wheel.
On 08/03/2010 10:23 AM, cassiope wrote:
> On Aug 2, 1:35 pm, Tim Wescott<t...@seemywebsite.com> wrote: >> On 08/02/2010 01:06 PM, nukeymusic wrote: >> >>> On Aug 2, 7:04 pm, cassiope<f...@u.washington.edu> wrote: >>>> On Aug 2, 7:50 am, nukeymusic<nukeymu...@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.
Yes, I cited that circuit to contradict Jim's statement that "you can't make a passive RC bandpass circuit", not to answer the OP's question. As I told the OP, I do dimly remember a passive RC circuit that had voltage (but certainly not power!) gain at some frequency. But I don't think it was a bandpass, and I don't know if one could build a bandpass version of it. If you could design a bandpass, passive, RC circuit with gain, then it would be a snap to design one with a 0dB peak. Realizing exactly a 0dB peak with component tolerances and all would be more of a trick, I'm sure. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html
On Aug 2, 1:35 pm, Tim Wescott <t...@seemywebsite.com> wrote:
> On 08/02/2010 01:06 PM, nukeymusic wrote: > > > On Aug 2, 7:04 pm, cassiope<f...@u.washington.edu>  wrote: > >> On Aug 2, 7:50 am, nukeymusic<nukeymu...@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.
On Aug 3, 7:24 am, Mark Freeman <a4533...@bofthew.com> wrote:
> Tim Wescott <t...@seemywebsite.com> wrote innews:SPednY_R0pRPY8vRnZ2dnUVZ_oednZ2d@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...@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