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FAQ (Frequently Asked Questions)
Category:
CDS 101/110 Fall 2004
Identifiers: H0 H1 H2 H3 H4 H5 H6 H7 H8 L0.0 L1.1 L1.2 L2.1 L2.2 L2.3 L3.1 L3.2 L4.1 L4.2 L5.1 L5.2 L6.1 L7.1 L9.1
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What is the definition of bandwidth?
Submitted by: waydo
Submitted on: November 10, 2004
Identifier:
L7.1
, H6
Bandwidth is the frequency at which the *closed-loop* transfer function has a gain of 1/sqrt(2) its DC value. That is, if G(s) is the closed-loop transfer function, the bandwidth is the frequency w at which |G(jw)|/|G(0)| = 1/sqrt(2). You may see it mentioned that the bandwidth is the frequency at which the *open-loop* transfer function has gain 1 (0 dB), but this is only a useful approximation for design purposes. The approximation rougly works because the closed-loop gain is about 1/(1+1) = 1/2 when the open-loop gain is 1, but an error is introduced by the phase of the open-loop transfer function at the crossover frequency. After doing a design, you should always verify the bandwidth of the closed-loop system.
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Where can I find definitions for gain margin, phase margin, and stability margin?
Submitted by: asa
Submitted on: November 14, 2004
Identifier:
L7.1
Look in section 7.4, pages 177 and 178 of the textbook, for these definitions.
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