28 December 2014 45 3K Report

I have asked this question with two purposes - first, at the request of Barrie Gilbert to terminate the irrelevant discussions in the question below...

https://www.researchgate.net/post/whats_the_real_behavior_of_rc_circuits

... and second, to answer the question of Erik Lindberg asked at the end of this discussion.

In the discussed arrangement (an RC circuit with various leakages), there are three resistances in parallel - R, Rc and Rv, and the equivalent resistance is Re = R||Rc||Rv. My idea is to connect a variable (N-shaped) negative resistor in parallel to Re and begin adjusting its resistance RN. Depending on its value, it will "eat" some part of Re and it will dissapear (become infinite):

1. RN = Rv (Rv is neutralized) or RN = Rc (Rc is neutralized)

2. RN = Rc||Rv (both Rc and Rv are neutralized)

3. RN = Rc||Rv||R (all the positive resistances are neutralized)

In case 2 (a load canceller), I thought we should obtain a perfect exponential shape... and this should solve the leakage problem. The next my idea was that if we continue decreasing this "destroying" negative resistance beyond this point of exact leakage neutralization, it will begin "eating" a part of the positive resistance of the "useful" resistor R... and finally (case 3), it will destroy all the resistance R. This means that the resistor R as though already has an infinite resistance... and behaves as an ideal current source... Actually, this is the idea of the Howland current source and its special case here - Deboo integrator. But while in the classic Deboo integrator the negative resistor (INIC) neutralizes only the positive resistance R, here it neutralizes all the resistances in parallel (the useful R and harmful leakages).

So, my question now is, "What happens if we try to neutralize all the positive resistances by an equivalent negative resistance (case 3)?"

My doubt is that, as a result of this 100% neutralization, this circuit will become unstable, and if the negative resistance begins dominating over the equivalent positive resistance, the effective resistance (the result of the neutralization) would become fully negative. And here, I suppose, the voltage across the capacitor will begin self-increasing in an avalanche like manner... From other side, the reactance of the capacitor C still remains... and it is a kind of a positive "resistance" (impedance)... and it turns out the circuit should remain stable...

The same problem exists in the Wien bridge oscillator... and it is solved there by applying a non-linear negative feedback in the INIC... Maybe it is possible to keep the circuit stable in a similar way?

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