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I decided to revisit this idea because I've noticed a few oscillators out there that have this mechanism at heart, but try to trace their origins from elsewhere. I'm by no means an expert on the subject but I do feel capable of a competent explanation, so here we go.
This circuit is more generally known as a type of Bistable Multivibrator; specifically, it is a Set/Reset Latch or SR Flip-flop. When it is being used as a bistable device, each of the bases act as an input (Set,Reset) and each of the collectors act as complementary outputs (Q,-Q).
At the instant the circuit is powered, neither transistor has the advantage and the circuit exists in unstable equilibrium between states. Heavy regenerative feedback between the opposing transistors acts to reinforce any small imbalances that develop. Which ever transistor happens to conduct best first is rapidly driven into saturation(ON) and the other into cut-off(OFF). If an input pulse of sufficient magnitude either drives the base of the ON transistor low or the base of the OFF transistor high, the circuit will switch states.
Now, suppose that if instead of using all that heavy feedback to switch between one of two stable states, you force the circuit to operate between states by placing an appropriate tuned RLC tank between your inputs(where I have the triangle and volt meter in this case). Once again, the circuit starts out in unstable equilibrium between states and any small imbalance is reinforced, but now, if either transistor saturates, the tank just swings the other way.
The circuit as I have drawn it here is probably the most basic manifestation of the concept, but there are countless ways to reinvent it into working oscillators. The tank can be simple or complicated, the transistors can be npn, pnp, nMOS, pMOS, or combinations, the frequency can be almost anything..
So to sum it up, the simple bistable multivibrator possesses a characteristic region of negative dynamic resistance between its differential inputs (and outputs) when biased between states. Under normal operation it can be thought of as the force that drives the circuit into one of its stable states by reinforcing any existing or applied instability.
I built this in EC 2.16 but that shouldn't matter.
I hope someone out there still cares and will benefit from this.
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