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I published an AGC VFO yesterday, but kept tweaking the design, and ended up with something like this. Now the AGC is better isolated at RF, because the integrating capacitor is at the high side end, where the RF swing usually is. This opened up a possibility for a more precise current mirror approach, which is somewhat self biasing. Also, the feedback is now a part of the oscillator. I figured that since parasitics are somewhat isolated and compressed, I might as well make good use of a proper impedance defined feedback. Even if there's a few pF of drift in BJT capacitances, they'd end up being dominated and compressed by the new feedback implementation.
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