Variable ramp generator

[Tim Ressel]

mb,
Many eons ago Paia made a toy synth called a Gnome. The VCO they used had a
"Skew" control that changed the output from a triangle to almost a saw. I have a
zipped .pdf file, but its 1.5 megs. let me know if you want it and I'll send it
your way.

Tim Ressel -- Hardware DQ
Hewlett-Packard
Verifone Division
916-630-2541
tim_r1 at verifone.com



> ----------
> From: 	mbartkow at ET.PUT.Poznan.PL[SMTP:mbartkow at ET.PUT.Poznan.PL]
> Sent: 	Tuesday, July 06, 1999 8:51 AM
> To: 	synth-diy at mailhost.bpa.nl
> Subject: 	Variable ramp generator
> 
> Dear all,
> 
> Taking the wavetable discussion aside, I have another problem
> and would love to hear your hints or comments.
> In fact, this is my idee-fixe for years:
> 
> I definitelly want to abandon the "mix several basic 
> waveforms" VCO approach. I just don't like it, because
> it trades too much pots for unnecessary stages of freedom.
> OTOH it is boring and yet another replication of an old and
> worn-out scheme. My idea for an original VCO is to generate
> a flexible waveform and shape it with some variable nonlinear 
> circuits.
> First of all I need a variable ramp waveform, i.e. a waveform,
> whereby the ratio of the rising edge to the falling one is
> freely adjustable without affecting the frequency. 
> I know, it is possible to independently control the charge and 
> discharge times in integrator by using a pair of diodes or 
> a CMOS switch. AFAIR, Juergen described such operation of KORG 
> LFOs. The problem is if one applies this control scheme to VCO 
> it leads to severe tracking problems.
> 
> My idea was to generate a stable saw or triangle and shape it
> using a switched gain circuit. I must say I tried to design such 
> a circuit, but either I am too narrow minded or blind - I just
> cannot come up with anything. I hope somebody invented this before
> and would not mind to share. 
> 
> mb
> 
> 
> --
> 
> Maciej Bartkowiak, PhD
> ========================================================================
> Institute of Electronics and Telecommunication     fax: (+48 61) 8782572
> Poznan University of Technology          phone: (+48 61) 8791016 int.171
> Piotrowo 3A                             email: mbartkow at et.put.poznan.pl
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> 
>