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Analog Filters: a Compilation of Standard Transfer Functions (UPDATED)

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--- Quote from: Dunckx on March 28, 2021, 10:28:14 pm ---I have just discovered that Zverev's "Filter Synthesis" book is out of copyright and may be downloaded from the Internet Archive for free!


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Great handbook I didn't know before, thank you!   :)

It even shows the "N-Path mixer"/"PolyPhase Mixer" at page 35/586, "Fig.1.33 The Digital Filter", recently discussed in

--- Quote from: Zverev's "Filter Synthesis" ---A   method   having   the   dimensions   of   a   genuine   breakthrough  is  shown  in  Fig.  1.33.   Here  the  mech-anical  commutators,  shown  schematically,  would   be   replaced  in  practice  by  transistor  diode  analog-gates  driven   by  conventional   logic  circuits  at  an   angular   velocity,  co0.  The  identical  RC  circuits  have  a  lowpass  response  which  is  so  modified  by  the  sampling  action  that    VJV2    exhibits    a   related    bandpass    response    centered    at    a>0.    This   method    shows   promise    of    yielding  figures  for   Q  and  stability  which  have  pre-viously    been   obtainable    only   with   crystal   filters.   Definite  results  on  the  performance  of  this  device  will  be    available  soon,  but  it  is too  new  to  be  evaluated  at  present.

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Yes, even Zverev referred to this commutating filter, which even predates Zverev's classic reference book by a few years!! However, these Discrete Time Continuous Amplitude (DTCA) filter concepts for other uses evaded general discovery until the Tayloe's Detector in the late 90s and then the PolyPhase, or N-Path Mixers ~2008. We did employ the DTCA commutating filter (as well as DTCA Chirp-Z techniques for Real Time SA) techniques in the early 80s for a narrow band tunable RF filter, but it took another 20~30 years for "other" uses of this very powerful technique to emerge!


For just getting to work on a filter without all the synthesis, Analog Devices has an awesome tool:


Define low/high/bandpass and passband/stopband needs, and boom you get a schematic.  Not only can you view mag/phase... you can specify cap and resistor tolerances and see the sensitivity envelope.  The recommended opamps are ADI, of course, but you can look up the gain-bandwidth and such to determine substitutions for each stage.  Plug it all into ltspice and fine tune.  ADI make great components, though I am more partial to ti opamps as they are usually cheaper than adi for the same performance, and cmos opamps (eg: opa2376) are finally getting into the realm of really low noise for low-power/low-volt applications.

I had a play with this a year back for use in my guitar amplifier. Without getting into the maths, if you want an active steep slopped high pass, low pass or bandpass filter you will get to a point where there is an unwanted peak just before the slope. In audio, the peak looks bad on paper but to the human ear it is pretty much undetected. In my case it was to attenuate everything below 120 hz before any distortion. But, a bit like any classic guitar amplifier with trebble middle and bass controls, you will be on for ever tweaking it then listening to it and chasing your tail.


--- Quote from: mawyatt on February 02, 2021, 06:39:39 pm ---For specific filter types, like Butterworth, Bessel, Chebyshev, Cauer and so on, Zverev's Handbook of Filter Synthesis is a great resource.

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Confession: That is the only book I have ever stolen from a library and never returned (40 years ago).


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