Vi w R Va SC₁ w Va R Vo + + + 1 店 SC₂ Vo HE by with such a transfer function. directly or cuit whose transfer function has a Butterworth polynomial in its denominator product of first- and second-order factors; therefore, we can construct a cir- Notice the form of the Butterworth polynomials in Table 15.1. They are the y cascading active filter circuits, each of which provides one of the needed factors. Figure 15.20 presents a block diagram of a cascade whose transfer function has a fifth-order Butterworth polynomial in its denominator. All odd-order Butterworth polynomials include the factor (s+ 1), so all odd-order Butterworth filter circuits must have a subcircuit with the transfer function H(s) = 1/(s + 1). This is the transfer function of the prototype low-pass active filter from Fig. 15.1. So what remains is to find a circuit whose transfer function has the form H(s) = 1/(s² + b₁s + 1). Such a circuit is shown in Fig. 15.21. To analyze this circuit, write the -domain KCL equations at the noninverting terminal of the op amp and at the node labeled V₁: Va - Vi R 0, Va - Vo +(Va - Vo)SC₁ + = R Vo - Va VosC2 + = 0. R ear Simplifying the two KCL equations yields - (2 + RC1s) Va (1 + RC₁s)V = Vi, simony-Va + (1 + RC25)V = 0. SC1 MAX3 w + R Va R + Vo SC2 1 s+1 1 s²+0.618s +1 1 Vo s²+1.618s +1 Figure 15.20 ▲ A cascade of first- and second-order circuits with the indicated trans- fer functions yielding a fifth-order low-pass Butterworth filter with we = 1 rad/s. Figure 15.21 ▲ A circuit that provides the second- order transfer function for the Butterworth filter cascade.
Vi w R Va SC₁ w Va R Vo + + + 1 店 SC₂ Vo HE by with such a transfer function. directly or cuit whose transfer function has a Butterworth polynomial in its denominator product of first- and second-order factors; therefore, we can construct a cir- Notice the form of the Butterworth polynomials in Table 15.1. They are the y cascading active filter circuits, each of which provides one of the needed factors. Figure 15.20 presents a block diagram of a cascade whose transfer function has a fifth-order Butterworth polynomial in its denominator. All odd-order Butterworth polynomials include the factor (s+ 1), so all odd-order Butterworth filter circuits must have a subcircuit with the transfer function H(s) = 1/(s + 1). This is the transfer function of the prototype low-pass active filter from Fig. 15.1. So what remains is to find a circuit whose transfer function has the form H(s) = 1/(s² + b₁s + 1). Such a circuit is shown in Fig. 15.21. To analyze this circuit, write the -domain KCL equations at the noninverting terminal of the op amp and at the node labeled V₁: Va - Vi R 0, Va - Vo +(Va - Vo)SC₁ + = R Vo - Va VosC2 + = 0. R ear Simplifying the two KCL equations yields - (2 + RC1s) Va (1 + RC₁s)V = Vi, simony-Va + (1 + RC25)V = 0. SC1 MAX3 w + R Va R + Vo SC2 1 s+1 1 s²+0.618s +1 1 Vo s²+1.618s +1 Figure 15.20 ▲ A cascade of first- and second-order circuits with the indicated trans- fer functions yielding a fifth-order low-pass Butterworth filter with we = 1 rad/s. Figure 15.21 ▲ A circuit that provides the second- order transfer function for the Butterworth filter cascade.
Electricity for Refrigeration, Heating, and Air Conditioning (MindTap Course List)
10th Edition
ISBN:9781337399128
Author:Russell E. Smith
Publisher:Russell E. Smith
Chapter7: Alternating Current, Power Distribution, And Voltage Systems
Section: Chapter Questions
Problem 5RQ
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