A simple VCO for an analog synthesizer

[David Hess]

Yes, that's right, the comparator controls the amplitude. However, at higher frequencies, the amplitude does tend to increase, due to the propagation delay of the comparator, the output tends to overshoot somewhat.

There is a variation where the output from the integrator drives the other comparator input through a resistor so bypassing the resistor with just the right capacitance triggers the comparator earlier as the frequency rises compensating for the delay and linearize the frequency versus voltage.

[Svgeesus]

Temperature and Vcc variations make a VCO design that stays in tune very difficult.  Some discussion here: Re: Syncing Synth VCOs

Another two useful resources on tempco for exponential converters:
www.openmusiclabs.com/files/expotemp.pdf
http://www.schmitzbits.de/expo_tutorial/

An example tricore oscillator circuit by Ian Fritz with a temperature compensated expo converter:
http://ijfritz.byethost4.com/sy_cir4.htm

And another by Thomas Henry
http://www.birthofasynth.com/Thomas_Henry/Pages/VCO-1.html#Design_Analysis:_The_Exponential_Converter