Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!hplabs!hpda!motcsd!mark
From: mark@motcsd.UUCP (Mark Jeghers)
Newsgroups: sci.electronics
Subject: Re: Square to Sawtooth
Message-ID: <288@greek.UUCP>
Date: 29 Mar 89 21:30:16 GMT
References: <7476@thorin.cs.unc.edu>
Reply-To: mark@greek.UUCP (Mark Jeghers)
Organization: Motorola Computer Systems, Cupertino, CA.
Lines: 33

In article <7476@thorin.cs.unc.edu> rohlf@unc.cs.unc.edu (John Rohlf) writes:
>
>		Given an externally generated square wave of varying 
>	frequency(audio range) and varying amplitude, what is the best/
>	easiest way of converting it to a sawtooth of the same frequency
>	and amplitude? 

A couple of methods of varying complexity/quality/cost:

A. Simple capacitor discharge setup.  Load the square wave output with
   a diode and a capacitor (and maybe a small resistor) such that the
   cap charges more or less instantaneously and discharges slowly.  The
   problem is that the quality is low and it works over a small range
   of frequencies.

B. A more complex version of "A", using a transistor to control the discharge
   rate of the cap.  Use the transistor as a "throttle", varying the discharge
   rate in inverse proportion to the frequency.  Complications: you must have
   a voltage or current available that varies with the frequency, also, I don't
   recall the exact wiring of the parts to achieve this effect.

C. The D/A approach.  Start with a square wave many octaves higher than what
   you want as your output.  Feed it to a binary counter, 7 or 8 bits wide
   for instance.  Feed that to an A/D converter and sawtooth will be output.
   It will contain staircases which can be filtered out.  Using more bits
   will reduce the staircases in size, but also require a higher initial
   frequency.  A square wave whose frequency matches the sawtooth can be
   taken directly off the lowest frequency bit of the binary counter.

Corrections/expansions/comments upon this are welcome.

Mark Jeghers
Motorola Computer Systems