[sdiy] VCO reset time

[René Schmitz]

Hi Harry and Ian,

>> 1)  What is a good ramp reset time ?   How fast have you seen ramp reset
>> be ?

Zero. (A special triangle core ;-))

> A carefully designed Terry Michaels type design will reset in around 
> 0.3-0.5 ms.  You can get a faster discharge by using a high current 

I'm pretty sure you mean us 0.3-0.5 us here.

> MOSFET, but then you run into serious problems with leakage and excess 
> capacitance.  Discharge rate is not the whole story, as has been 
> discussed here numerous times.

Right, one thing to keep in mind is the maximum slew rate your opamps 
can handle. Its no use to discharge any faster than the slew rate of the 
opamps can handle. It only leads to overshooting behaviour. (I ran into 
that with the thyratron VCO for example.) Or put the other way arround 
the faster you can discharge the faster your whole chain needs to be, 
and the better opamps you need. I have often intentionally increased the 
discharge time to get a cleaner output.

>> 2) How many octaves do you expect (in tune) without resorting to HF
>> compensation
> 
> 
> Depends what you mean by "in tune".  I don't suppose you want to tell us 
> that, either.  :-)

Hmm, a discharge of 300ns is 1/3000th of the cycle of a 1kHz. That would 
mean that at 1kHz you're off by 0.3Hz and at 10khz you're off by 3Hz....

Cheers,
  René

-- 
uzs159 at uni-bonn.de
http://www.uni-bonn.de/~uzs159