From: user@example.net   
      
   On 2/13/2026 11:34 AM, john larkin wrote:   
   > On Fri, 13 Feb 2026 06:40:05 -0900, Christopher Howard   
   >  wrote:   
   >   
   >> piglet  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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