Newsgroups: sci.electronics
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Square to Sawtooth
Message-ID: <1989Apr1.215144.21913@utzoo.uucp>
Organization: U of Toronto Zoology
References: <7476@thorin.cs.unc.edu> <65200002@hpl-opus.HP.COM> <1989Mar30.164612.28073@utzoo.uucp> <7518@fluke.COM>
Date: Sat, 1 Apr 89 21:51:44 GMT

In article <7518@fluke.COM> strong@tc.fluke.COM (Norm Strong) writes:
>}>Find a VCO that has a unit-amplitude sawtooth as an auxiliary output.
>}
>}It's trivial to build such a thing, by the way:  an integrator integrating
>}the input, a comparator for "reached the top", and a one-shot feeding an
>}analog switch to reset the integrator.
>
>	How would you make the circuit so that the sawtooth starts at zero on
>the leading edge of the square wave, and reaches maximum just as the square
>wave falls.  Let this be a steady state repetitive waveform.  Manual
>adjustments are not permitted.  
>
>Now, isn't that more interesting?

No, not very, actually:  this is what phase-locked loops are for.  Barring
unusual situations like very high frequencies, a $5 4046 kills this problem
dead.  (Why do you think I was building a sawtooth VCO?)  Sometimes you need
a bit of ingenuity in the surrounding circuitry to get the details right,
but automatically synchronizing a generated waveform with an external one
is basically a solved problem.  Getting the amplitude to match is actually
the hardest part of the original problem.

The advent of one-chip phase-locked loops, analog switches, and high-quality
op amps has reduced a lot of such analog signal-processing problems to
trivialities.  It only gets sticky when the cheap, convenient chips are
ruled out by demanding requirements like very high speed or very high
precision.
-- 
Welcome to Mars!  Your         |     Henry Spencer at U of Toronto Zoology
passport and visa, comrade?    | uunet!attcan!utzoo!henry henry@zoo.toronto.edu