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Re: cheap analog square function?

Date	2026-02-13 13:00 -0500
Subject	Re: cheap analog square function?
Newsgroups	sci.electronics.design
References	<877bslbhl7.fsf@librehacker.com> <10mlh77$1q347$1@dont-email.me> <87ms1cd54a.fsf@librehacker.com> <kcjuokh8omf235trh6iu0oknoe2ds78nla@4ax.com>
From	bitrex <user@example.net>
Message-ID	<698f66ea$0$22$882e4bbb@reader.netnews.com> (permalink)

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On 2/13/2026 11:34 AM, john larkin wrote:
> On Fri, 13 Feb 2026 06:40:05 -0900, Christopher Howard
> <christopher@librehacker.com> wrote:
> 
>> piglet <erichpwagner@hotmail.com> writes:
>>
>>> If high precision is not needed and only LF response is enough then I
>>> have used PWM techniques:
>>>
>>> Circuit A is the basic squaring concept, relies on modern open-drain
>>> output comparators being pretty good switches to ground. Assumes you
>>> already have a source of sawtooth or triangle waves with defined zero
>>> and peak values in the system.
>>>
>>
>> Could you please explain better how the PWM squarer circuit works? It
>> look like it would be easy to build, but I don't grasp what is going on.
> 
> A fairly simple single-opamp or comparator circuit can convert input V
> to a duty cycle n. A transistor or analog switch or even a diode can
> multiply V * n. Lowpass filter that and you have V^2.
> 
> 
> John Larkin
> Highland Tech Glen Canyon Design Center
> Lunatic Fringe Electronics

It has the advantage that the analog switch and passive low pass filter 
don't affect the DC performance, so long as you can afford the settling 
time of the filter.

The hassle of trying to kludge cheap parts into decent multipliers, 
particularly ones with decent DC performance, and keep the signal path 
totally analog is that every cheap op amp and resistor you add to try to 
correct for the deficiency of all the other cheap parts tends to add 
noise and offset and soon enough you lose more than you gain.

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cheap analog square function? Christopher Howard <christopher@librehacker.com> - 2026-02-09 14:52 -0900
  Re: cheap analog square function? john larkin <jl@glen--canyon.com> - 2026-02-09 16:47 -0800
  Re: cheap analog square function? Don Y <blockedofcourse@foo.invalid> - 2026-02-09 17:50 -0700
  Re: cheap analog square function? "Edward Rawde" <invalid@invalid.invalid> - 2026-02-09 20:03 -0500
  Re: cheap analog square function? Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2026-02-10 02:05 +0000
  Re: cheap analog square function? Jan Panteltje <alien@comet.invalid> - 2026-02-10 05:50 +0000
    Re: cheap analog square function? bitrex <user@example.net> - 2026-02-10 03:39 -0500
  Re: cheap analog square function? Bill Sloman <bill.sloman@ieee.org> - 2026-02-10 18:05 +1100
    Re: cheap analog square function? John R Walliker <jrwalliker@gmail.com> - 2026-02-10 08:41 +0000
      Re: cheap analog square function? bitrex <user@example.net> - 2026-02-10 03:46 -0500
        Re: cheap analog square function? bitrex <user@example.net> - 2026-02-10 03:49 -0500
  Re: cheap analog square function? antispam@fricas.org (Waldek Hebisch) - 2026-02-10 14:12 +0000
    Re: cheap analog square function? Christopher Howard <christopher@librehacker.com> - 2026-02-10 07:49 -0900
      Re: cheap analog square function? Don Y <blockedofcourse@foo.invalid> - 2026-02-10 11:40 -0700
      Re: cheap analog square function? john larkin <jl@glen--canyon.com> - 2026-02-10 11:39 -0800
        Re: cheap analog square function? Bill Sloman <bill.sloman@ieee.org> - 2026-02-11 23:38 +1100
          Re: cheap analog square function? john larkin <jl@glen--canyon.com> - 2026-02-11 07:56 -0800
            Re: cheap analog square function? Buzz McCool <buzz_mccool@yahoo.com> - 2026-02-11 09:30 -0800
              Re: cheap analog square function? john larkin <jl@glen--canyon.com> - 2026-02-11 09:38 -0800
                Re: cheap analog square function? liz@poppyrecords.invalid.invalid (Liz Tuddenham) - 2026-02-11 18:52 +0000
                Re: cheap analog square function? bitrex <user@example.net> - 2026-02-11 14:22 -0500
                Re: cheap analog square function? john larkin <jl@glen--canyon.com> - 2026-02-11 12:14 -0800
                Re: cheap analog square function? bitrex <user@example.net> - 2026-02-11 15:35 -0500
                Re: cheap analog square function? john larkin <jl@glen--canyon.com> - 2026-02-11 13:04 -0800
                Re: cheap analog square function? bitrex <user@example.net> - 2026-02-11 16:35 -0500
                Re: cheap analog square function? Lasse Langwadt <llc@fonz.dk> - 2026-02-11 21:41 +0100
                Re: cheap analog square function? Jeroen Belleman <jeroen@nospam.please> - 2026-02-11 22:49 +0100
            Re: cheap analog square function? Lasse Langwadt <llc@fonz.dk> - 2026-02-11 21:37 +0100
            Re: cheap analog square function? Bill Sloman <bill.sloman@ieee.org> - 2026-02-12 17:36 +1100
              Re: cheap analog square function? john larkin <jl@glen--canyon.com> - 2026-02-12 10:19 -0800
                Re: cheap analog square function? Lasse Langwadt <llc@fonz.dk> - 2026-02-12 21:05 +0100
                Re: cheap analog square function? john larkin <jl@glen--canyon.com> - 2026-02-12 14:12 -0800
                Re: cheap analog square function? Lasse Langwadt <llc@fonz.dk> - 2026-02-12 23:39 +0100
                Re: cheap analog square function? john larkin <jl@glen--canyon.com> - 2026-02-12 15:19 -0800
                Re: cheap analog square function? Don Y <blockedofcourse@foo.invalid> - 2026-02-12 18:13 -0700
                Re: cheap analog square function? Gerhard Hoffmann <dk4xp@arcor.de> - 2026-02-13 00:38 +0100
                Re: cheap analog square function? john larkin <jl@glen--canyon.com> - 2026-02-12 16:09 -0800
                Re: cheap analog square function? Gerhard Hoffmann <dk4xp@arcor.de> - 2026-02-13 02:42 +0100
                Re: cheap analog square function? john larkin <jl@glen--canyon.com> - 2026-02-13 09:30 -0800
                Re: cheap analog square function? Jan Panteltje <alien@comet.invalid> - 2026-02-14 06:14 +0000
                Re: cheap analog square function? Glen Walpert <nospam@null.void> - 2026-02-14 14:18 +0000
                Re: cheap analog square function? john larkin <jl@glen--canyon.com> - 2026-02-14 07:51 -0800
                Re: cheap analog square function? Jan Panteltje <alien@comet.invalid> - 2026-02-15 06:27 +0000
                Re: cheap analog square function? john larkin <jl@glen--canyon.com> - 2026-02-14 07:47 -0800
                Re: cheap analog square function? Jan Panteltje <alien@comet.invalid> - 2026-02-15 06:50 +0000
                Re: cheap analog square function? mas@example.com - 2026-02-16 07:38 +0000
                Re: cheap analog square function? Jan Panteltje <alien@comet.invalid> - 2026-02-16 08:49 +0000
              Re: cheap analog square function? legg <legg@nospam.magma.ca> - 2026-02-14 08:57 -0500
  Re: cheap analog square function? piglet <erichpwagner@hotmail.com> - 2026-02-12 21:37 +0000
    Re: cheap analog square function? Christopher Howard <christopher@librehacker.com> - 2026-02-13 06:40 -0900
      Re: cheap analog square function? john larkin <jl@glen--canyon.com> - 2026-02-13 08:34 -0800
        Re: cheap analog square function? bitrex <user@example.net> - 2026-02-13 13:00 -0500
          Re: cheap analog square function? john larkin <jl@glen--canyon.com> - 2026-02-13 10:52 -0800
        Re: cheap analog square function? bitrex <user@example.net> - 2026-02-13 13:01 -0500
      Re: cheap analog square function? piglet <erichpwagner@hotmail.com> - 2026-02-13 19:36 +0000
        Re: cheap analog square function? john larkin <jl@glen--canyon.com> - 2026-02-13 12:06 -0800
          Re: cheap analog square function? piglet <erichpwagner@hotmail.com> - 2026-02-13 20:42 +0000
            Re: cheap analog square function? john larkin <jl@glen--canyon.com> - 2026-02-15 12:43 -0800
        Re: cheap analog square function? Christopher Howard <christopher@librehacker.com> - 2026-02-16 09:36 -0900
          Re: cheap analog square function? Bill Sloman <bill.sloman@ieee.org> - 2026-02-18 00:03 +1100
            Re: cheap analog square function? john larkin <jl@glen--canyon.com> - 2026-02-17 08:06 -0800
        Re: cheap analog square function? Christopher Howard <christopher@librehacker.com> - 2026-02-16 13:08 -0900
          Re: cheap analog square function? piglet <erichpwagner@hotmail.com> - 2026-02-17 11:40 +0000
            Re: cheap analog square function? Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2026-02-17 12:34 -0500
              Re: cheap analog square function? Gerhard Hoffmann <dk4xp@arcor.de> - 2026-02-17 18:57 +0100
                Re: cheap analog square function? Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2026-02-17 18:18 +0000
                Re: cheap analog square function? Gerhard Hoffmann <dk4xp@arcor.de> - 2026-02-17 19:39 +0100
                Re: cheap analog square function? Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2026-02-17 14:00 -0500
                Re: cheap analog square function? Bill Sloman <bill.sloman@ieee.org> - 2026-02-18 15:10 +1100
              Re: cheap analog square function? Bill Sloman <bill.sloman@ieee.org> - 2026-02-18 14:43 +1100
          Re: cheap analog square function? Bill Sloman <bill.sloman@ieee.org> - 2026-02-18 01:43 +1100
      Re: cheap analog square function? Jan Panteltje <alien@comet.invalid> - 2026-02-14 05:53 +0000

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