[sdiy] They aren't sawtooths, they're ramps

[cheater cheater]

David,
couldn't you have something that would 'exaggerate' the part that
triggers the op amp?

Say, you could have a hard-clipper based circuit that amplifies the
signal that goes out of the bounds allowed by the clipper - like you
can do in a normal wave shaper. You could amplify by 10 times. Maybe
you can make that clipper very precise so that it only creates big
spikes on the very top and bottom of the triangle wave. In that case,
wouldn't those spikes give enough voltage difference for the switch to
flip quickly? 'speedup spikes' as they were..

D.

On Fri, Nov 6, 2009 at 04:33, David G. Dixon <dixon at interchange.ubc.ca> wrote:
> John, it's not really like that.  When the triangle approaches the
> threshold, the trigger output starts to fall very gradually.  In fact, it
> takes several microseconds to fall a few millivolts.  It's as if the
> threshold is not very sharp.  Once the fall or rise in trigger output
> voltage is noticeable, then it curves downward about 0.5V over about 150ns,
> and then makes the final transition through zero very quickly, in less than
> 50ns.  I'm not sure how much all of this contributes to tracking errors -- I
> think it still tracks very well.
>
> On the other hand, the LM318 trigger is very sharp.  Of course, with a
> speedup cap, it spikes well above and below the rail voltages, but I don't
> think this will have any adverse effect.
>
>
>> >The discrete version takes about 200ns to switch.  It takes about 150ns
>> to
>> >make up its mind, but then the actual switching takes place very fast,
>> >within about 50ns.  However, it doesn't begin switching very swiftly.
>>
>> Can you speed up the "make up its mind" part by feeding some bias to
>> the transistor so that it's closer to the switching threshold?
>>
>> Keep in mind that I'm virtually clueless. (Alright, Harry -- I'm
>> totally clueless! ;-)
>
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