π/2 -π/2 Jo ffof2 (a) (b) (c) Fig10 Resonant curve of the series resonant circuit and phase-frequency relation (3)quality factor of resonant circuit. (I)definition of O and the voltage allocation. From Im=U/R,we can obtain the voltage of resistor,capacitor and inductor is UR=IR=U U U1=1nZ,=元0L R (26) U,1 Uc-1aZe=RoC =UL While resonance occurs,the ratio of inductor voltage UL(or voltage on capacitor U)to the total voltage is called quality factor,denoted by 0=4-0L0= U R or U @RC (27) When the total voltage is fixed,higher the is,larger UL and Uc are.O is a physical quantity to characterize the quality of a resonant circuit. (II)the frequency selectivity of resonant circuit. The most important application of resonant circuits in wireless technology is signal selection.In order to illustrate the quality of frequency selectivity,usually the bandwidth is defined as the distance betweenon both side of the resonant peak.sshown in Fig.11 △f=方2-f (28) =U)-方 (29) It can be proved that the bandwidth Af is inversely proportional to Q,thus8 （3）quality factor of resonant circuit. （I）definition of Q and the voltage allocation. From Im = U/R，we can obtain the voltage of resistor, capacitor and inductor is UR = I m R = U L R U UL = I m ZL = ω0 （26） C m C U L R C U U = I Z = ⋅ = 0 1 ω While resonance occurs, the ratio of inductor voltage UL (or voltage on capacitor Uc) to the total voltage is called quality factor, denoted by Q R L U U Q L ω0 = = or U RC U Q ω0 C 1 = = （27） When the total voltage is fixed, higher the Q is , larger UL and UC are. Q is a physical quantity to characterize the quality of a resonant circuit. （II）the frequency selectivity of resonant circuit. The most important application of resonant circuits in wireless technology is signal selection. In order to illustrate the quality of frequency selectivity, usually the bandwidth is defined as the distance between ( ) m I = 1 2 I on both side of the resonant peak. As shown in Fig. 11 2 1 Δf = f − f （28） () ( ) 2 1 2 mI I f = I f = （29） It can be proved that the bandwidth Δf is inversely proportional to Q , thus O f R Z f 0 f 0 f 1 f 2 O I I m I m 2 f f 0 O f (a) (b) (c) Fig10 Resonant curve of the series resonant circuit and phase-frequency relation