[sdiy] true VCOs, expo ?

[Aaron Lanterman]

On Sun, 4 Feb 2007, tony Rolando wrote:

> http://www.national.com/pf/LM/LM358.html

> Also, is this an example of a true Voltage Controlled osc. (as opposed to 
> current controlled)? Or is that 100k resistor (R) at the CV input a voltage 
> to current? Is there a such thing as a true "voltage controlled" oscillator?

Well... the distinction gets a bit pedantic... You could replace that 100k 
resistance with some kind of other current source and happily go along 
your merry way.

If you think about most voltage-to-voltage op amp circuits with the + 
terminal at some fixed voltage, you see that the input impedance more or 
less is turning a voltage to a current, and the feedback impedance is 
turning that current back into a voltage.

I like to tell my students that while the most commonly known op amp 
circuits represent quantities as voltages, they do the actual computation 
via currents. Hence, you'll almost never see me use mesh-current analysis 
in my class. It's all node-voltage analysis, since I think more insight is 
to be gained that way.

- Aaron

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