Sawtooth generators

[Duane R Balvage]

        Good afternoon (at least on the west coast)!

      I noticed a small problem with sawtooth generators that use a capacitor

    discharged through a cmos gate or FET.... The capacitor discharge rate

    is FIXED, even though the frequency changes. Consider this :



                         FIG.1


----------------------------------------------V+
          /|            ----
         / |          /    |         
        /  |         /     |      /|    /|
       /   |        /      |     / |___/ |  
  _______________________________________________gnd
~
    mid freq        low freq      hi freq



        as long as the f in ~= discharge rate of cap, you get nice

 saw waves. BUT, at low frequencies, the cap charges up to max, and then

 stays there @ that voltage until the gate turns on again, resulting

 in waveform B (not a very good saw wave, although it may sound interesting).

 At high frequencies >> discharge rate, the cap is never allowed to charge

 completely, resulting in a low output, inverted version of waveform

 B. (see waveform C).    


    This is just something I observed (thought?) and I figured it might

 help in this discussion about sawtooth generators.....

                  direct any questions, comments, design ideas to:
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