The top answer says that if you use DC current source, then the Q point is the "solution" of the circuit.
I interpret this as, if you use a DC current source of I amps, then the Q point will tell you what voltage will appear across the nonlinear device (e.g. diode)
But on this page, it says we can have multiple Q points, some are stable, some are unstable.
Can someone confirm my understanding of Q point and elaborate on the meaning of having multiple Q points?
Is quantum tunnel diode the only device having multiple Q points?
Best Answer
Most devices have a single solution for the Q or operating point. e.g. NPN transistor (graph 1).
However, there are a number of devices that exhibit a region of dynamic negative resistance (dV/dI = -R). In this region you could have three Q points. (Graph 2) Q1 and Q3 would be deemed as 'stable' because in this region they behave as a normal resistance (increase voltage, increase current) . Q2 is unstable because it acts as an negative resistance.
Note that these regions are not actual negative resistance, only the slope (dV/dI) which is negative. This dynamic negative resistance is often used to cancel out the resistance of an LC circuit creating a high Q filter circuit or even an oscillator.
Probably the first device to have this characteristic was the screen grid tetrode valve (tube).