[sdiy] VCO tuning philosophy re-visited

[lanterma at ece.gatech.edu]

On Feb 6, 2011, at 10:44 PM, David wrote:

> Where can I learn more about high frequency compensation and how it works?
> Where can I learn more about why high frequencies droop?

There's a good discussion of this in the Hal Chamberlin MAM book. It's probably based at least partially on an earlier discussion in Electronotes. I don't have my copy of MAM with me (it's at the work office) so I'm not sure.

As an aside, there's another kind of design called a "charge pump" that I think avoids the droop issue; instead of discharging the integrator cap through a "resistor" (i.e. a FET or some other transistor acting as a switch), it actually shoves current in the opposite direction. The Rhodes Chroma oscillator does this. I think the ultrasonic VCO Ian Fritz uses in his Double Decka (huh, it came up again) does something like that too, although I may be getting that mixed up with one of Ian's other VCO designs, or getting it mixed up with something entirely non-Ian related. In other words I should probably just stop typing now. ;)

- Aaron