awalker@topaz.rutgers.edu (*Hobbit*) (02/28/88)
All the references I can conveniently get my hands on at the moment seem to be from '78 or so, sadly out of date. Are there any VCO chips that do square/ triangle/whatever outputs that require a minimum of external parts? Cheap? I want to build a project with a whole pile of [probably triangle] oscillators modulating each other. _H*
max@trinity.uucp (Max Hauser) (02/29/88)
In article <18403@topaz.rutgers.edu> awalker@topaz.rutgers.edu (*Hobbit*) writes: >... Are there any VCO chips that do square/ >triangle/whatever outputs that require a minimum of external parts? Cheap? Indeed many of the good parts still being used were designed in the 1970s and so reference data from 1978 may still be useful. With the caveat that it has been a few years since I looked at the range of oscillator chips available, I recall the very successful line from Exar Integrated Systems, designed by Al Grebene et al., sort of a second generation of VCO circuits, following the earlier very successful oscillators in phased-locked loops at Signetics (560, 561, 562, 565, 566, 567). The Exar parts include the 205, a wide-bandwidth square/triangle generator capable of Megahertz frequencies, and the 2206, a submegahertz oscillator often used for audio, with square, triangle and sinewave outputs. If someone has experience with more recent easy-to-use oscillator chips, please post (I'm curious too). It's worth noting that virtually without exception, circuits marketed as "voltage-controlled" triangle-wave oscillators are forms of relaxation oscillators and operate internally, at the core, as *current*-controlled oscillators, to which the designers have usually added a voltage-to-current converter circuit. This is because it is easy to derive fundamental timing, over a wide controllable range, in a triangle generator from the ratio of a current and a capacitance; and yet a voltage, not a current, is the usual external frequency-control signal that users want to apply. Often the limits to accuracy in the VCO's voltage/frequency relation derive from the voltage-current conversion and not from the relaxation-oscillator core. Also, in many circuits it's possible to override the V-I converter and impose your own external current control if you really want high control accuracy or wide range. Sometimes the designers provide explicitly for this, but sometimes (as with the Signetics 565-566-567) you have to get tricky. Max Hauser / max@eros.berkeley.edu / ...{!decvax}!ucbvax!eros!max
rep@genrad.UUCP (Pete Peterson) (02/29/88)
In article <18403@topaz.rutgers.edu> awalker@topaz.rutgers.edu (*Hobbit*) writes: >All the references I can conveniently get my hands on at the moment seem to be >from '78 or so, sadly out of date. Are there any VCO chips that do square/ >triangle/whatever outputs that require a minimum of external parts? Cheap? >I want to build a project with a whole pile of [probably triangle] oscillators >modulating each other. > There may be newer, better, fancier parts available, but the 8038 Waveform-generator/VCO has been around for a long time, is made by EXAR, Intersil, and probably others. It can be swept over something like a 30:1 frequency range, and will go from something like a milliherz (!) to about 300 khz. It puts out square-waves and triangle-waves and uses a nonlinear network to convert the triangle waves to fairly reasonable sine waves. It wants a 10-30 volt supply (or +/-5 to +/-15). It is listed with a price of $2.79 in my 1987 Active Electronics Catalog (a good place to buy random parts for home projects). I have used these theings and they are easy to make work and use a minimum of external components. pete peterson {decvax,linus,wjh12,mit-eddie,masscomp}!genrad!rep