Could anyone simplify the concept of a Resonance Circuit? My understanding of the concept of resonance is very basic, that it increases the amplitude of a frequency when another is added and they are in phase and or something like that.
As said BP Lathi, to apply a signal at the input of a system (circuit) with frequency that matches one of its natural modes is like: "Throw gasoline on the fire." This is resonance. A very small signal, leads to a very large output. In a limit situation, the input can be zero and the output be finite (infinite gain). Such natural modes are actually the complex conjugate poles of this system. Therefore, only systems (passive circuits) with order higher than 2 and having complex poles can resonate. In other words, only LC or RLC circuits. With the help of feedback and very high gain amplifiers is also possible to use only RL or RC networks (this apparatus can generate complex poles).