Hello Everyone,
the stability problem(such like poles and so on) normally only exists in closed loop circuit?
But if there is a circuit without feedback, does the stability problem still presents?
Are there still poles?
Passive (and frequency dependent) circuits have poles with a real part which is negative (left hand side of the s-plane). Therefore they always are stable.
If such networks are used in active feedback circuits these poles change theit position and can move towards the Im-axis. As a consequence, the stability degrades. When the poles are on the Im-axis (real part zero) or even in the right hand half of the plane the circuit is unstable.