How Do You Factor Transfer Functions in S-Plane Analysis?

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SUMMARY

The forum discussion centers on the factoring of transfer functions in S-plane analysis, specifically the transfer function H(s) = (2s + 1) / (s^2 + 5s + 6). The user expresses confusion over the correct factoring process, questioning the transition from H(s) to H(s) = (1/2) * ((s + 1/2) / ((s + 3)(s + 2))). The key misunderstanding lies in the algebraic manipulation of the numerator and denominator, where the user mistakenly believes that factoring out 2 from the numerator should not involve altering the denominator. The response clarifies that the original factoring presented is indeed correct.

PREREQUISITES
  • Understanding of S-plane analysis
  • Familiarity with transfer functions
  • Basic algebraic manipulation skills
  • Knowledge of pole-zero plots
NEXT STEPS
  • Review algebraic techniques for factoring polynomials
  • Study the principles of S-plane analysis in control systems
  • Explore examples of transfer function manipulation in engineering textbooks
  • Learn about pole-zero analysis and its applications in filter design
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Students and professionals in electrical engineering, particularly those focusing on control systems and filter design, will benefit from this discussion.

FrankJ777
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Hi all. I'm trying to relearn S-plane analysis and filter transfer functions. What I'm having problems with is simple algebra i think, because it's been a while. Right now I've been reading http://www.ee.up.ac.za/main/_media/en/undergrad/subjects/eli220/polezero.pdf. What I'm confused about, among other things, is factoring the transfer function H(s).
In their example:

H(s) = \frac{2s + 1}{(s^2 + 5S + 6)}

factored

H(s) = \frac{1}{2} \frac{s+1/2}{(s+3)(s+2)}

I don't understand how they get that. The way I see it, because:
2s+1 = 2(s+1/2)
and
s^{2}+5s+6 = (s+3)(s+2)
so

H(s) = \frac{2s + 1}{(s^2 + 5S + 6)} = \frac{2}{1} \frac{s+1/2}{(s+3)(s+2)}

Also It seems that:

\frac{2s + 1}{(s^2 + 5S + 6)} ≠ \frac{1}{2} \frac{s+1/2}{(s+3)(s+2)}

So I guess what I don't understand is why it seems that instead of factoring out 2 from the numerator, we are dividing the numerator by 2 and multiplying the denominator by 2.

Can someone please set me straight. I know I did this a few years ago and it seemed to make more sense then, than it does now.

Thanks a lot.
 
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Hi FrankJ777. The explanation is quite simple: you are right and they are wrong. :smile:
 
Really? I hope that's the case. Too bad I wasted several study hours trying to get it.

Thanks
 

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