[sdiy] Re: Sawtooth phase shifter

[harrybissell]

Magnus Danielson wrote:

> Both these designs is fairly easy to understand if one draws the waveforms,
> make notes about voltages and is able to sum properly. Simulation is trivial
> actually. If your simulation tool fails, toss it since by brain obviously beats
> it. Not a good benchmark, but anyways...

I'm not sure that I agree.  I have several sawtooth phase shifter designs.
They all simulate correctly.  Yours doesn't.  That does not mean that yours
does not work... I just want to

1) be sure that the .pdf is correct. I googled "sawtooth phase shifter" and got
you link at
home.swipnet.se/cfmd/synths/ schematics/sawphaseshift.pdf

2) understand 'why' the simulation is failing.

I have a design with five resistors and two opamps (same as yours) that
does simulate correctly...  In both cases I'm assuming that the TL07x is capable
of swinging about 13.5V with a 15V supply.  I verify that I have CV of +/-5V
and sawtooth input of +/- 5V.  The comparator gives the correct PWM and shifts
correctly... but the output stage gives a pwm wave as well... no hint of sawtooth
at all (let alone phase shifted saw).

Sure... I have had simulations fail before. But never one this simple...

H^) harry

>
>
> Cheers,
> Magnus
>
> > KD
> >
> > --- karl dalen <dalenkarl at yahoo.se> skrev:
> >
> > > Folks!
> > >
> > > You dont need any super specialized clipping things,
> > > nor any 4000gates for supersharp edges (even if its nice to have,
> > > well if you want absolute precision it can be neat to have ,
> > > but the rounding of the saw wave, and retrace time at high
> > > frequencies will "showel bang" it up anyway) no specialized
> > > CV inputs for phase! (who asked for that?) ugh, and ugh again!!
> > >
> > > You need:
> > > 1: a saw wave, 0 to +5v or 10V in peak unipolar or bipolar.
> > > 2: a PW wave ,0 to +5v or 10V in peak unipolar or bipolar.
> > > 3. add them with 100PW/50saw blend in amplitude and you get saw phase
> > > shifting.
> > > 4: add them 100saw/100PW and you get phase shifting saw wave, 0-180 degrees.
> > > 5: The sawphase wizzard has spoken,thank you very much! :-)
> > >
> > > After words:
> > > In any additive wave thing in wich phased saw waves actuaclly are
> > > wave amplitude are the crucical inferno. So dont base your phase
> > > waves on the asumption of stable power supplies! ugh!.
> > > Its very simmliare to the basic saw to triangle converters!
> > >
> > > > The problem is that the first op-amp acts as a comparator, so that may
> > > > confuse
> > > > the hell out of you if your model does not saturate. The assumed supply
> > > > voltage
> > > > is +/- 15V, which is "all over the schematic" ;O)
> > > >
> > > > KD tried it ages ago, and then it worked well! ;O)
> > >
> > > Right, ages and ages ago! Ooh, now im starting to feel very old and crippled!
> > >
> > > Reg
> > > KD
> > >
> >