From: erichpwagner@hotmail.com   
      
   On 16/02/2026 22:08, Christopher Howard wrote:   
   >>>>   
   >>>> 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.   
   >>>>   
   >>   
   >   
   > I had a few follow questions, if you please, regarding the PWM squarer   
   > (circuit A):   
   >   
   > - Does this circuit work in quadrant one only? If so, would any slight   
   >    modification of the circuit allow for handling negative input voltages   
   >    also?   
   >   
   > - Could you please tell me a little bit more about the low pass filter   
   >    portion of the circuit? Does that particular configuration have a   
   >    name?   
   >   
      
   The circuit I showed gives output of zero for negative inputs (the input   
   would always be below even the lowest point of the ramp so the   
   comparator output would always be low).   
      
   To handle negative inputs precede it with a precision full wave   
   rectifier aka absolute value circuit.   
      
   Good place to look for examples:   
      
      
   Any low pass filter would do, right up from a single stage RC to as high   
   order super steep as you want. It has to reduce the chopping rate from   
   the sawtooth or triangle wave switching to a residual ripple low enough   
   for your accuracy needs. Getting high precision and with low ripple to   
   follow fast changing inputs will demand high frequencies and steeper   
   filtering. The dynamics compromises happen there.   
      
   For example my units used a tri wave at 50-60kHz and I happened to use a   
   second order 2kHz filter. That topology shewn is called Sallen & Key but   
   there are many others. I chose those values for no particular reason, it   
   was good enough for the job. Desirable is the filter has high input   
   impedance and probably low output impedance, depending on what the next   
   stage is.   
      
   One (of many) good places to read more:   
      
      
   piglet   
      
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