Chapter 6
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The sinusoidal frequency response (or,
simply, frequency response) of a circuit
provides a measure of how the circuit
responds to sinusoidal inputs of arbitrary
frequency.
The frequency response of a circuit is a
measure of the variation of a load-related
voltage or current as a function of the
frequency of the excitation signal.
A circuit model
Thévenin equivalent source circuit
Complete equivalent circuit
VL( jω) is a phase-shifted and amplitudescaled version of VS( jω).
Filters
Low-Pass Filters
A simple RC filter
Magnitude and phase response plots for RC
filter
High-Pass Filters
High-pass filter
Frequency response of a high-pass filter
Bandpass Filters, Resonance, and Quality Factor
RLC bandpass filter
Frequency responses of RLC bandpass filter
Resonance and Bandwidth
(a) Normalized magnitude response of second-order bandpass filter;
(b) normalized phase response of second-order bandpass filter
Bode Plots
Frequency response plots of linear systems are often
displayed in the form of logarithmic plots, called Bode
plots, where the horizontal axis represents frequency on
a logarithmic scale (base 10) and the vertical axis
represents the amplitude ration or phase of the
frequency response function. In Bode plots the
amplitude ratio is expressed in units of decibels (dB),
where
Bode plots for low-pass RC filter; the frequency variable is
normalized to ω/ωο. (a) Magnitude response; (b) phase response
Bode plots for high-pass RC filter. (a) Magnitude response;
(b) phase response