Pulse and Digital Circuits

3.4 RLC CIRCUITS

RLC circuits behave altogether differently when compared to either RL or RC circuits. RLC circuits are resonant circuits. These can be either series resonant circuits or parallel resonant circuits. A parallel RLC circuit is used as a tank circuit in an oscillator to generate oscillations (this is the feedback network that produces the phase shift of 180°). The RLC circuit is also used in tuned amplifiers to select a desired frequency band at the output. When a sinusoidal signal is applied as input to a series RLC circuit [see Fig. 3.23(a)], the frequency-vs-current characteristic is as shown in Fig. 3.23(b).

At resonance: X_L = X_C

FIGURE 3.23(a) An RLC series circuit with sinusoidal input; (b) the frequency-vs-current characteristic ...