[工学]电路理论 华科电气Chapter 14 Frequency Response.pptVIP

RESONANCE (谐振) 14.2. Series Resonance (串联谐振) Resonance results when the imaginary part of impedance Z is zero. Resonant frequency： Notice： The impedance is purely resistive, thus Z=R. The LC series combination acts like a short circuit, and the entire voltage is across R. Quality factor of a series resonant circuit (品质因数)： The quality factor is a measure of the selectivity of the circuit, dimensionless. 14.3. Parallel Resonance （并联谐振 ） Resonance occurs when the imaginary part of Y is zero. Notice： The parallel LC combination acts like an open circuit, so that the entire currents flows through R. The inductor and capacitor current can be much more than the source current at resonance. ?0： series resonance ?1：parallel resonance ?1 ?0 L1 = 100mH，if Zin(103)= ∞，determine C1；if Zin(500)= 0，keep C1 unchanged, determine C2。 solution： 例：测电感L的电阻与电感，角频率?=103 rad/s，IS=1A，C=50μF时，电压表读数为最大，U=50V。求R、L。 解： 14.5 Passive Filters A filter is a circuit that is designed to pass signals with desired frequencies and reject or attenuate others. Passive filter：consists of only passive elements R, L and C. Active filter：consists of active elements such as transistors and op amps in addition to passive elements. 高通滤波器：A highpass filter is designed to pass all frequencies above its cutoff frequency ?C. 带通滤波器：A bandpass filter is designed to pass all frequecncies within a band of frequencies, ?1??2. 带阻滤波器：A bandstop filter is designed to stop or eliminate all frequencies within a band of frequencies, ?1??2. 14.6 Active Filters 14.6 Active Filters An Example：Telephone Three major limits to the passive filters: They cannot generate gain greater than 1; They may require bulky and expensive inductors; They perform poorly at frequencies below the audio frequency range(300Hzf3000Hz). Passive filters are useful at high frequencies. * * CHAPTER 14 FREQUENCY RESPONSE 14.1 Introduction 14.2 Series Resonance 14.3 Parallel Resonance 14.4 Transfer Function 14.5 Passive Filters 14.6 Active