Aufgaben:Exercise 3.4: Attenuation and Phase Response: Difference between revisions

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{{quiz-Header|Buchseite=Lineare zeitinvariante Systeme/Laplace–Transformation und p–Übertragungsfunktion
{{quiz-Header|Buchseite=Linear_and_Time_Invariant_Systems/Laplace_Transform_and_p-Transfer_Function
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[[File:P_ID1768__LZI_A_3_4.png|right|]]
[[File:P_ID1768__LZI_A_3_4.png|right|frame|Pole-zero diagram and definition of some auxiliary quantities]]
:Wir gehen vom skizzierten Pol–Nullstellen–Diagramm aus, also von den Werten
We assume the sketched pole–zero diagram, i.e. the values
:$$K \hspace{-0.25cm} = \hspace{-0.2cm}5, \hspace{0,2cm}Z = 1, \hspace{0,2cm}N = 2, \\
:$$K = 5, \hspace{0,2cm}Z = 1, \hspace{0,2cm}N = 2, $$
p_{\rm  o}\hspace{-0.25cm} = \hspace{-0.2cm} 1,\hspace{0,2cm}p_{\rm  x1}= -3 + 3{\rm j},\hspace{0,2cm}p_{\rm  x2}= -3 - 3{\rm j}\hspace{0.05cm} .$$
:$$ p_{\rm  o}= 1,\hspace{0,2cm}p_{\rm  x1}= -3 + 3{\rm j},\hspace{0,2cm}p_{\rm  x2}= -3 - 3{\rm j}\hspace{0.05cm} .$$


:Damit lautet die <i>p</i>&ndash;Übertragungsfunktion:
Thus,&nbsp; the&nbsp; $p$&ndash;transfer function is:
:$$H_{\rm L}(p)= K \cdot \frac {p - p_{\rm o }}
:$$H_{\rm L}(p)= K \cdot \frac {p - p_{\rm o }}{(p - p_{\rm x 1})(p - p_{\rm x 2})}\hspace{0.05cm} .$$
{(p - p_{\rm x 1})(p - p_{\rm x 2})}
\hspace{0.05cm} .$$


:Mit der Substitution <i>p</i> = j &middot; 2&pi;<i>f</i> lässt sich die herkömmliche Übertragungsfunktion angeben, die auch als Frequenzgang bezeichnet wird:
Considering the substitution &nbsp;$p = {\rm j} \cdot 2 \pi f$,&nbsp; the conventional transfer function can be specified,&nbsp; which is also called&nbsp; "frequency response":
:$$H(f) =  H_{\rm L}(p)\Bigg |_{\hspace{0.1cm} p\hspace{0.05cm}=\hspace{0.05cm}{\rm j \hspace{0.05cm}2\pi \it
:$$H(f) =  H_{\rm L}(p)\Bigg |_{\hspace{0.1cm} p\hspace{0.05cm}=\hspace{0.05cm}{\rm j \hspace{0.05cm}2\pi \it f}} =  {\rm e}^{-a(f)\hspace{0.05cm}}\cdot {\rm e}^{- \hspace{0.05cm}{\rm j} \hspace{0.05cm}\cdot \hspace{0.05cm}b(f)}\hspace{0.05cm}.$$
f}} =  {\rm e}^{-a(f)\hspace{0.05cm}}\cdot {\rm e}^{- \hspace{0.05cm}{\rm j} \hspace{0.05cm}\cdot \hspace{0.05cm}b(f)}
\hspace{0.05cm}.$$


:Aus dieser Gleichung erkennt man auch den Zusammenhang zwischen <i>H</i>(<i>f</i>), der Dämpfungsfunktion <i>a</i>(<i>f</i>) und der Phasenfunktion <i>b</i>(<i>f</i>). Für eine durch den Punkt <i>p</i> = j2&pi;<i>f</i> indirekt vorgegebene Frequenz <i>f</i> kann man die entsprechenden Dämpfungs&ndash; und Phasenwerte wie folgt ermitteln:
From this equation it can also be seen the relationship between
:$$a(f)\hspace{0.15cm}{\rm in}\hspace{0.15cm}{\rm Np} \hspace{0.25cm} =  \hspace{0.2cm} -{\rm ln} \hspace{0.1cm} K
*the transfer function &nbsp;$H(f)$,  
+ {\rm ln} \hspace{0.1cm} |R_{\rm x1}|+{\rm ln} \hspace{0.1cm} |R_{\rm x1}|- {\rm ln} \hspace{0.1cm} |R_{{\rm o} }|\hspace{0.05cm}
*the attenuation function &nbsp;$a(f)$&nbsp; and
,\\
*the phase function &nbsp;$b(f)$.  
b(f)\hspace{0.15cm}{\rm in}\hspace{0.15cm}{\rm rad} \hspace{0.25cm} =  \hspace{0.2cm}
\phi_{\rm x1}+ \phi_{\rm x2}-\phi_{\rm o}
\hspace{0.05cm} .$$


:Die entsprechenden Beträge |<i>R</i><sub>o</sub>|, |<i>R</i><sub>x1</sub>| und |<i>R</i><sub>x2</sub>| können Sie ebenso wie die Winkel <i>&#981;</i><sub>0</sub>, <i>&#981;</i><sub>x1</sub> und <i>&#981;</i><sub>x2</sub> der Grafik entnehmen.


:<b>Hinweis:</b> Die Aufgabe bezieht sich auf das Kapitel 3.2.
The attenuation and phase values can be determined as follows for a frequency &nbsp;$f$&nbsp; indirectly specified by the point&nbsp; $p = {\rm j} \cdot 2 \pi f$&nbsp;:
:$$a(f)\hspace{0.15cm}{\rm in}\hspace{0.15cm}{\rm Np} \hspace{0.25cm} =  \hspace{0.2cm} -{\rm ln} \hspace{0.1cm} K+ {\rm ln} \hspace{0.1cm} |R_{\rm x1}|+{\rm ln} \hspace{0.1cm} |R_{\rm x1}|- {\rm ln} \hspace{0.1cm} |R_{{\rm o} }|\hspace{0.05cm},$$
:$$ b(f)\hspace{0.15cm}{\rm in}\hspace{0.15cm}{\rm rad} \hspace{0.25cm} =  \hspace{0.2cm}\phi_{\rm x1}+ \phi_{\rm x2}-\phi_{\rm o}\hspace{0.05cm} .$$


===Fragebogen===
The corresponding magnitudes &nbsp;$|R_{\rm o}|$,  &nbsp;$|R_{\rm x1}|$ &nbsp;and&nbsp; $|R_{\rm x2}|$ as well as the angles &nbsp;$\phi_{\rm o}$, &nbsp;$\phi_{\rm x1}$ &nbsp;and&nbsp; $\phi_{\rm x2}$&nbsp; can be taken from the graph .
 
 
 
 
 
Please note:
*The exercise belongs to the chapter&nbsp; [[Linear_and_Time_Invariant_Systems/Laplace_Transform_and_p-Transfer_Function|Laplace Transform and p-Transfer Function]].
 
 
 
 
===Questions===


<quiz display=simple>
<quiz display=simple>
{Berechnen Sie <i>H</i>(<i>f</i>). Wie groß ist dessen Betrag bei sehr großen Frequenzen?
{Compute &nbsp;$H(f)$.&nbsp; What is its magnitude at very large frequencies?
|type="{}"}
|type="{}"}
$|H_L(f &#8594; &#8734;)|$ = { 0 3% }
$|H(f &#8594; &#8734;)| \ = \ $ { 0. }




{Berechnen Sie den Betragsfrequenzgang und den Dämpfungswert für <i>f</i> &#8594; 0.
{Compute the magnitude frequency response and the attenuation value for &nbsp;$f &#8594 0$.
|type="{}"}
|type="{}"}
$|H(f = 0)|$ = { 0.278 3% }
$|H(f = 0)| \ = \ $ { 0.278 3% }
$|a(f = 0)|$ = { 1.281 3% } $Np$
$a(f = 0) \ = \ $ { 1.281 3% } $\ \rm Np$




{Berechnen Sie gemäß der beschriebenen Vorgehensweise den Dämpfungswert bei <i>f</i> = 4/(2&pi;) in Neper (Np) und Dezibel (dB).
{Compute the attenuation value at &nbsp;$f =4/(2 \pi)$&nbsp; in neper&nbsp; $\rm(Np)$&nbsp; and decibel&nbsp; $\rm(dB)$&nbsp; according to the described approach.
|type="{}"}
|type="{}"}
$a(f = 2/ \pi)$ = { 0.155 3% } $Np$
$a(f = 2/ \pi)\ = \ $ { 0.155 3% } $\ \rm Np$
$a(f = 2/ \pi)$ = { 1.346 3% } $dB$
$a(f = 2/ \pi)\ = \ $ { 1.346 3% }$\ \rm dB$




{Berechnen Sie gemäß der beschriebenen Vorgehensweise den Phasenwert bei der Frequenz <nobr><i>f</i> = 4/(2&pi;).</nobr>
{Compute the phase value at frequency &nbsp;$f = 4/(2 \pi)$ according to the described approach.
|type="{}"}
|type="{}"}
$b(f = 2/ \pi)$ = - { 18.8 3% } $Grad$
$b(f = 2/ \pi)\ = \ $ { -19.3--18.3 } $\ \rm Grad$




Line 58: Line 65:
</quiz>
</quiz>


===Musterlösung===
===Solution===
{{ML-Kopf}}
{{ML-Kopf}}
:<b>1.</b>&nbsp;&nbsp;Die <i>p</i>&ndash;Übertragungsfunktion lautet:
'''(1)'''&nbsp; The&nbsp; $p$&ndash;transfer function is:
:$$H_{\rm L}(p)= K \cdot \frac {p - p_{\rm o }}
:$$H_{\rm L}(p)= K \cdot \frac {p - p_{\rm o }}{(p - p_{\rm x 1})(p - p_{\rm x 2})}\hspace{0.05cm} .$$
{(p - p_{\rm x 1})(p - p_{\rm x 2})}
 
  \hspace{0.05cm} .$$
*The conventional transfer function&nbsp; (the frequency response)&nbsp; is obtained via the substitution &nbsp;$p = {\rm j} \cdot 2 \pi f$:
:$$H(f)= K \cdot \frac {{\rm j \hspace{0.05cm}2\pi \it f} - p_{\rm o }}{({\rm j \hspace{0.05cm}2\pi \it f} - p_{\rm x 1})({\rm j \hspace{0.05cm}2\pi \it f} - p_{\rm x 2})}= {\rm e}^{-a(f)\hspace{0.05cm}}\cdot {\rm e}^{- \hspace{0.05cm}{\rm j} \hspace{0.05cm}\cdot \hspace{0.05cm}b(f)}\hspace{0.05cm} .$$*In the limiting case &nbsp;$f &#8594; \infty$,&nbsp; the following is obtained for the magnitude,&nbsp; attenuation and phase::$$\lim_{f \hspace{0.05cm}\rightarrow \hspace{0.05cm}\infty}  H(f)= \frac{K}{{\rm j \hspace{0.05cm}2\pi \it f}}\hspace{0.15cm}\Rightarrow \hspace{0.15cm}\lim_{f \hspace{0.05cm}\rightarrow \hspace{0.05cm}\infty}  |H(f)|\hspace{0.15cm}\underline {= 0} \hspace{0.05cm}\Rightarrow \hspace{0.15cm}\lim_{f \hspace{0.05cm}\rightarrow \hspace{0.05cm}\infty}  a(f)= \infty,\hspace{0.1cm}\lim_{f \hspace{0.05cm}\rightarrow \hspace{0.05cm}\infty}  b(f)\underline {={\pi}/{2}\hspace{0.1cm}(+90^\circ)}\hspace{0.01cm}.$$
 


:Zur herkömmlichen Übertragungsfunktion (Frequenzgang) kommt man mit der Substitution <i>p</i> = j &middot; 2&pi;<i>f</i>:
:$$H(f)= K \cdot \frac {{\rm j \hspace{0.05cm}2\pi \it
f} - p_{\rm o }}
{({\rm j \hspace{0.05cm}2\pi \it
f} - p_{\rm x 1})({\rm j \hspace{0.05cm}2\pi \it
f} - p_{\rm x 2})}
=  {\rm e}^{-a(f)\hspace{0.05cm}}\cdot {\rm e}^{- \hspace{0.05cm}{\rm j} \hspace{0.05cm}\cdot \hspace{0.05cm}b(f)}
\hspace{0.05cm} .$$


:Im Grenzfall <i>f</i> &#8594; &#8734; ergibt sich für den Betrag, die Dämpfung und die Phase:
'''(2)'''&nbsp; From the general equation in subtask&nbsp; '''(1)'''&nbsp; the following is obtained with the limit process &nbsp;$f &#8594 0$:
:$$\lim_{f \hspace{0.05cm}\rightarrow \hspace{0.05cm}\infty}  H(f)= \frac{K}{{\rm j \hspace{0.05cm}2\pi \it
[[File:P_ID1769__LZI_A_3_4_d_neu.png|right|frame|Magnitude&nbsp; (&rArr; Betrag)&nbsp; $|H(f)|$,&nbsp; <br>attenuation&nbsp; (&rArr; Dämpfung)&nbsp; $a(f)$&nbsp; and phase&nbsp; $b(f)$]]
f}}\hspace{0.15cm}\Rightarrow \hspace{0.05cm}\lim_{f \hspace{0.05cm}\rightarrow \hspace{0.05cm}\infty}   |H(f)|\hspace{0.15cm}\underline {= 0} \hspace{0.05cm}
:$$|H(f=0)|= -\frac {K \cdot p_{\rm o }}{p_{\rm x 1}\cdot p_{\rm x 2}}\frac {5 \cdot 1}{(-3 + 3{\rm j})\cdot (-3 + 3{\rm j})}\frac {5 }{18}\hspace{0.15cm}\underline {\approx0.278}\hspace{0.05cm} ,$$
\Rightarrow \hspace{0.05cm}\lim_{f \hspace{0.05cm}\rightarrow \hspace{0.05cm}\infty}  a(f)= \infty,\hspace{0.1cm}
:$$a(f=0)=- {\rm ln} \hspace{0.1cm}\hspace{0.15cm}\underline { |H(f=0)|= 1.281\,{\rm Np }}\hspace{0.05cm} .$$
\lim_{f \hspace{0.05cm}\rightarrow \hspace{0.05cm}\infty}  b(f)=
\frac{\pi}{2}\hspace{0.1cm}(90^\circ)
\hspace{0.01cm}.$$


:<b>2.</b>&nbsp;&nbsp;Aus der allgemeinen Gleichung in a) erhält man mit dem Grenzübergang <i>f</i> &#8594; 0:
The screen capture of the Flash&ndash;module&nbsp; "Causal Systems"&nbsp; summarizes the results of this exercise:
:$$|H(f=0)|=  -\frac {K \cdot p_{\rm o }}
:*middle axis (blue): &nbsp; magnitude $|H(f)|$, &nbsp; &rArr; &nbsp; here labeled with&nbsp; $|Y(f)|$,
{p_{\rm x 1}\cdot p_{\rm x 2}}
:*left axis (red): &nbsp; attenuation&nbsp; $a(f)$,
=  \frac {5 \cdot 1}{
:*right axis (green): &nbsp; phase&nbsp; $b(f)$.
(-3 + 3{\rm j})\cdot (-3 + 3{\rm j})}=  \frac {5 }{18}\hspace{0.15cm}\underline {\approx
:*black point: &nbsp; values for&nbsp; $2\pi f = 4.$
  0.278}
\hspace{0.05cm} ,$$
:$$a(f=0)=- {\rm ln} \hspace{0.1cm}\hspace{0.15cm}\underline { |H(f=0)|= 1.281\,{\rm Np }}
\hspace{0.05cm} .$$
[[File:P_ID1769__LZI_A_3_4_d_neu.png|right|]]
:Die Grafik fasst die Ergebnisse dieser Aufgabe zusammen:<br><br>


:Mittlere Achse (blau): Betrag,<br>
:Linke Achse (rot): Dämpfung,<br>
:Rechte Achse (grün): Phase.<br><br>
:Schwarzer Punkt:2&pi;<i>f</i> = 4.
<br><br>


:Bildschirmabzug des Flash&ndash;Moduls &bdquo;Kausale Systeme&rdquo;.<br><br>
[[File:P_ID2843__LZI_A_3_4.png|right|frame|Pole-zero diagram and some auxiliary quantities]]
'''(3)'''&nbsp; According to the detailed description in the &nbsp;[[Linear_and_Time_Invariant_Systems/Laplace_Transform_and_p-Transfer_Function#Graphical_determination_of_attenuation_and_phase|theory part]],&nbsp; the following holds for the attenuation function:


:<b>3.</b>&nbsp;&nbsp;Entsprechend der detaillierten Beschreibung im Theorieteil gilt für die Dämpfungsfunktion:
:$$a(f)=  -{\rm ln} \hspace{0.1cm} K+ {\rm ln} \hspace{0.1cm} |R_{\rm x1}|+{\rm ln} \hspace{0.1cm} |R_{\rm x2}|- {\rm ln} \hspace{0.1cm} |R_{{\rm o} }|\hspace{0.05cm} .$$
[[File:P_ID2843__LZI_A_3_4.png|right|]]
:$$a(f)=  -{\rm ln} \hspace{0.1cm} K
+ {\rm ln} \hspace{0.1cm} |R_{{\rm x1}}|+{\rm ln} \hspace{0.1cm} |R_{{\rm x1}}|- {\rm ln} \hspace{0.1cm} |R_{{\rm o} }|\hspace{0.05cm} .$$


:Zu berücksichtigen ist die Zusatzeinheit &bdquo;Neper&rdquo; (Np).
*Furthermore,&nbsp; the additional unit&nbsp; "neper"&nbsp; $\rm (Np)$&nbsp; must be taken into account.
*The attenuation at &nbsp;$f = 2/\pi$&nbsp; is searched-for.&nbsp; For this, we set &nbsp;$p = {\rm j} \cdot 2 \pi f = 4$&nbsp; and determine the following distances:
:$$R_{\rm o} = 1 - 4 \cdot {\rm j}, \hspace{0.2cm}|R_{\rm o}| \hspace{0.25cm} =  \hspace{0.2cm} \sqrt{1^2 + 4^2}= 4.123, \hspace{1.15cm}{\rm ln} \hspace{0.1cm}|R_{\rm o}|\hspace{0.25cm} =  \hspace{0.2cm}1.417\,{\rm Np }\hspace{0.05cm},$$
:$$R_{\rm x1} = -3 - 1 \cdot {\rm j}, \hspace{0.2cm}|R_{\rm x1}| \hspace{0.25cm} =  \hspace{0.2cm} \sqrt{3^2 + 1^2}= 3.162,\hspace{0.5cm}{\rm ln} \hspace{0.1cm}|R_{\rm x1}|\hspace{0.25cm} =  \hspace{0.2cm}1.151\,{\rm Np }\hspace{0.05cm},$$
:$$ R_{\rm x2} = -3 - 7 \cdot{\rm j},\hspace{0.2cm}|R_{\rm x2}| \hspace{0.25cm} =  \hspace{0.2cm} \sqrt{3^2 + 7^2}= 7.616,\hspace{0.5cm}{\rm ln} \hspace{0.1cm}|R_{\rm x2}|\hspace{0.25cm} =  \hspace{0.2cm}2.030\,{\rm Np }\hspace{0.05cm}.$$
$$\Rightarrow \hspace{0.3cm}a(f = \frac{4}{2\pi})=-{\rm ln} \hspace{0.1cm} 5+ 1.151+ 2.030-1.417\hspace{0.15cm}\underline{=0.155\,{\rm Np }}\hspace{0.05cm}.$$


:Gesucht ist der Dämpfungswert bei <i>f</i> = 2/&pi;. Dazu setzen wir <i>p</i> = j &middot; 2&pi;<i>f</i> = 4 und ermitteln folgende Abstände:
This is equivalent to &nbsp; $0.155\  {\rm Np} \cdot  8.686 \  {\rm dB/Np} \hspace{0.15cm} \underline{= 1.346 \ {\rm dB}}$.
:$$R_{\rm o} = 1 - 4 \cdot {\rm j}, \hspace{0.2cm}|R_{\rm o}| \hspace{0.25cm} =  \hspace{0.2cm} \sqrt{1^2 + 4^2}= 4.123,\\ {\rm ln} \hspace{0.1cm}|R_{\rm o}|
\hspace{0.25cm} = \hspace{0.2cm}1.417\,{\rm Np }\hspace{0.05cm},\\
R_{\rm x1} = -3 - 1 \cdot {\rm
j}, \hspace{0.2cm}|R_{\rm x1}| \hspace{0.25cm} = \hspace{0.2cm} \sqrt{3^2 + 1^2}= 3.162,\\
  {\rm ln} \hspace{0.1cm}|R_{\rm x1}|
  \hspace{0.25cm} = \hspace{0.2cm}1.151\,{\rm Np }\hspace{0.05cm},\\
R_{\rm x2} = -3 - 7 \cdot{\rm j},
\hspace{0.2cm}|R_{\rm x2}| \hspace{0.25cm} =  \hspace{0.2cm} \sqrt{3^2 + 7^2}= 7.616,\\
{\rm ln} \hspace{0.1cm}|R_{\rm x2}|
  \hspace{0.25cm} =  \hspace{0.2cm}2.030\,{\rm Np }\hspace{0.05cm}.$$
:$$\Rightarrow \hspace{0.3cm}a(f = \frac{4}{2\pi})=
-{\rm ln} \hspace{0.1cm} 5
+ 1.151+ 2.030-
1.417=0.155\,{\rm Np }
\hspace{0.05cm}.$$


:Das entspricht 0.155 Np &middot; 8.686 dB/Np <u>= 1.346 dB</u>.


:<b>4.</b>&nbsp;&nbsp;Nach der detaillierten Beschreibung im Theorieteil gilt wegen <i>K</i> > 0 für die Phasenfunktion:
'''(4)'''&nbsp; The following holds for the phase function according to the description in the theory section due to &nbsp;$K > 0$&nbsp;:
:$$b(f ={2}/\pi) = \phi_{\rm x1} + \phi_{\rm x1}-\phi_{\rm o}\hspace{0.05cm},$$
:$$b(f ={2}/\pi) = \phi_{\rm x1} + \phi_{\rm x2}-\phi_{\rm o}\hspace{0.05cm},$$
:$$\phi_{\rm x1} \hspace{0.25cm} = \hspace{0.2cm} {\rm arctan}\hspace{0.15cm}(1/3) =
:$$\phi_{\rm x1} ={\rm arctan}\hspace{0.15cm}(1/3) =18.4^\circ\hspace{0.05cm}, \hspace{0.5cm}\phi_{\rm x2} = {\rm arctan}\hspace{0.15cm}(7/3)  =66.8^\circ\hspace{0.05cm},\hspace{0.5cm} \phi_{\rm o} = {\rm arctan}\hspace{0.15cm}(-1/4) =180^\circ - 76^\circ = 104^\circ $$
18.4^\circ\hspace{0.05cm}, \hspace{0.2cm}\phi_{\rm x2} = {\rm arctan}\hspace{0.15cm}(7/3)  =
:$$ \Rightarrow \hspace{0.3cm}b(f ={2}/\pi) =18.4^\circ + 66.8^\circ - 104^\circ  \hspace{0.15cm} \underline{= -18.8^\circ}\hspace{0.05cm}.$$
66.8^\circ\hspace{0.05cm},\\
\phi_{\rm o} \hspace{0.25cm} = \hspace{0.2cm} {\rm arctan}\hspace{0.15cm}(-1/4) =
180^\circ - 76^\circ = 104^\circ$$
:$$\Rightarrow \hspace{0.3cm}b(f ={2}/\pi) =
18.4^\circ + 66.8^\circ - 104^\circ  \hspace{0.15cm} \underline{= -18.8^\circ}
\hspace{0.05cm}.$$
{{ML-Fuß}}
{{ML-Fuß}}






[[Category:Aufgaben zu Lineare zeitinvariante Systeme|^3.2 Laplace–Transformation und p–Übertragungsfunktion^]]
[[Category:Linear and Time-Invariant Systems: Exercises|^3.2 Laplace Transform and p-Transfer Function^]]
[[de:Aufgaben:Aufgabe 3.4: Dämpfungs- und Phasenverlauf]]

Latest revision as of 17:57, 16 March 2026

Pole-zero diagram and definition of some auxiliary quantities

We assume the sketched pole–zero diagram, i.e. the values

$$K = 5, \hspace{0,2cm}Z = 1, \hspace{0,2cm}N = 2, $$
$$ p_{\rm o}= 1,\hspace{0,2cm}p_{\rm x1}= -3 + 3{\rm j},\hspace{0,2cm}p_{\rm x2}= -3 - 3{\rm j}\hspace{0.05cm} .$$

Thus,  the  $p$–transfer function is:

$$H_{\rm L}(p)= K \cdot \frac {p - p_{\rm o }}{(p - p_{\rm x 1})(p - p_{\rm x 2})}\hspace{0.05cm} .$$

Considering the substitution  $p = {\rm j} \cdot 2 \pi f$,  the conventional transfer function can be specified,  which is also called  "frequency response":

$$H(f) = H_{\rm L}(p)\Bigg |_{\hspace{0.1cm} p\hspace{0.05cm}=\hspace{0.05cm}{\rm j \hspace{0.05cm}2\pi \it f}} = {\rm e}^{-a(f)\hspace{0.05cm}}\cdot {\rm e}^{- \hspace{0.05cm}{\rm j} \hspace{0.05cm}\cdot \hspace{0.05cm}b(f)}\hspace{0.05cm}.$$

From this equation it can also be seen the relationship between

  • the transfer function  $H(f)$,
  • the attenuation function  $a(f)$  and
  • the phase function  $b(f)$.


The attenuation and phase values can be determined as follows for a frequency  $f$  indirectly specified by the point  $p = {\rm j} \cdot 2 \pi f$ :

$$a(f)\hspace{0.15cm}{\rm in}\hspace{0.15cm}{\rm Np} \hspace{0.25cm} = \hspace{0.2cm} -{\rm ln} \hspace{0.1cm} K+ {\rm ln} \hspace{0.1cm} |R_{\rm x1}|+{\rm ln} \hspace{0.1cm} |R_{\rm x1}|- {\rm ln} \hspace{0.1cm} |R_{{\rm o} }|\hspace{0.05cm},$$
$$ b(f)\hspace{0.15cm}{\rm in}\hspace{0.15cm}{\rm rad} \hspace{0.25cm} = \hspace{0.2cm}\phi_{\rm x1}+ \phi_{\rm x2}-\phi_{\rm o}\hspace{0.05cm} .$$

The corresponding magnitudes  $|R_{\rm o}|$,  $|R_{\rm x1}|$  and  $|R_{\rm x2}|$ as well as the angles  $\phi_{\rm o}$,  $\phi_{\rm x1}$  and  $\phi_{\rm x2}$  can be taken from the graph .



Please note:



Questions

1 Compute  $H(f)$.  What is its magnitude at very large frequencies?

$|H(f → ∞)| \ = \ $

2 Compute the magnitude frequency response and the attenuation value for  $f &#8594 0$.

$|H(f = 0)| \ = \ $
$a(f = 0) \ = \ $ $\ \rm Np$

3 Compute the attenuation value at  $f =4/(2 \pi)$  in neper  $\rm(Np)$  and decibel  $\rm(dB)$  according to the described approach.

$a(f = 2/ \pi)\ = \ $ $\ \rm Np$
$a(f = 2/ \pi)\ = \ $ $\ \rm dB$

4 Compute the phase value at frequency  $f = 4/(2 \pi)$ according to the described approach.

$b(f = 2/ \pi)\ = \ $ $\ \rm Grad$


Solution

(1)  The  $p$–transfer function is:

$$H_{\rm L}(p)= K \cdot \frac {p - p_{\rm o }}{(p - p_{\rm x 1})(p - p_{\rm x 2})}\hspace{0.05cm} .$$
  • The conventional transfer function  (the frequency response)  is obtained via the substitution  $p = {\rm j} \cdot 2 \pi f$:
$$H(f)= K \cdot \frac {{\rm j \hspace{0.05cm}2\pi \it f} - p_{\rm o }}{({\rm j \hspace{0.05cm}2\pi \it f} - p_{\rm x 1})({\rm j \hspace{0.05cm}2\pi \it f} - p_{\rm x 2})}= {\rm e}^{-a(f)\hspace{0.05cm}}\cdot {\rm e}^{- \hspace{0.05cm}{\rm j} \hspace{0.05cm}\cdot \hspace{0.05cm}b(f)}\hspace{0.05cm} .$$*In the limiting case  $f → \infty$,  the following is obtained for the magnitude,  attenuation and phase::$$\lim_{f \hspace{0.05cm}\rightarrow \hspace{0.05cm}\infty} H(f)= \frac{K}{{\rm j \hspace{0.05cm}2\pi \it f}}\hspace{0.15cm}\Rightarrow \hspace{0.15cm}\lim_{f \hspace{0.05cm}\rightarrow \hspace{0.05cm}\infty} |H(f)|\hspace{0.15cm}\underline {= 0} \hspace{0.05cm}\Rightarrow \hspace{0.15cm}\lim_{f \hspace{0.05cm}\rightarrow \hspace{0.05cm}\infty} a(f)= \infty,\hspace{0.1cm}\lim_{f \hspace{0.05cm}\rightarrow \hspace{0.05cm}\infty} b(f)\underline {={\pi}/{2}\hspace{0.1cm}(+90^\circ)}\hspace{0.01cm}.$$


(2)  From the general equation in subtask  (1)  the following is obtained with the limit process  $f &#8594 0$:

$, 
attenuation  (⇒ Dämpfung)  $a(f)$  and phase  $b(f)$
$$|H(f=0)|= -\frac {K \cdot p_{\rm o }}{p_{\rm x 1}\cdot p_{\rm x 2}}= \frac {5 \cdot 1}{(-3 + 3{\rm j})\cdot (-3 + 3{\rm j})}= \frac {5 }{18}\hspace{0.15cm}\underline {\approx0.278}\hspace{0.05cm} ,$$
$$a(f=0)=- {\rm ln} \hspace{0.1cm}\hspace{0.15cm}\underline { |H(f=0)|= 1.281\,{\rm Np }}\hspace{0.05cm} .$$

The screen capture of the Flash–module  "Causal Systems"  summarizes the results of this exercise:

  • middle axis (blue):   magnitude $|H(f)|$,   ⇒   here labeled with  $|Y(f)|$,
  • left axis (red):   attenuation  $a(f)$,
  • right axis (green):   phase  $b(f)$.
  • black point:   values for  $2\pi f = 4.$


Pole-zero diagram and some auxiliary quantities

(3)  According to the detailed description in the  theory part,  the following holds for the attenuation function:

$$a(f)= -{\rm ln} \hspace{0.1cm} K+ {\rm ln} \hspace{0.1cm} |R_{\rm x1}|+{\rm ln} \hspace{0.1cm} |R_{\rm x2}|- {\rm ln} \hspace{0.1cm} |R_{{\rm o} }|\hspace{0.05cm} .$$
  • Furthermore,  the additional unit  "neper"  $\rm (Np)$  must be taken into account.
  • The attenuation at  $f = 2/\pi$  is searched-for.  For this, we set  $p = {\rm j} \cdot 2 \pi f = 4$  and determine the following distances:
$$R_{\rm o} = 1 - 4 \cdot {\rm j}, \hspace{0.2cm}|R_{\rm o}| \hspace{0.25cm} = \hspace{0.2cm} \sqrt{1^2 + 4^2}= 4.123, \hspace{1.15cm}{\rm ln} \hspace{0.1cm}|R_{\rm o}|\hspace{0.25cm} = \hspace{0.2cm}1.417\,{\rm Np }\hspace{0.05cm},$$
$$R_{\rm x1} = -3 - 1 \cdot {\rm j}, \hspace{0.2cm}|R_{\rm x1}| \hspace{0.25cm} = \hspace{0.2cm} \sqrt{3^2 + 1^2}= 3.162,\hspace{0.5cm}{\rm ln} \hspace{0.1cm}|R_{\rm x1}|\hspace{0.25cm} = \hspace{0.2cm}1.151\,{\rm Np }\hspace{0.05cm},$$
$$ R_{\rm x2} = -3 - 7 \cdot{\rm j},\hspace{0.2cm}|R_{\rm x2}| \hspace{0.25cm} = \hspace{0.2cm} \sqrt{3^2 + 7^2}= 7.616,\hspace{0.5cm}{\rm ln} \hspace{0.1cm}|R_{\rm x2}|\hspace{0.25cm} = \hspace{0.2cm}2.030\,{\rm Np }\hspace{0.05cm}.$$

$$\Rightarrow \hspace{0.3cm}a(f = \frac{4}{2\pi})=-{\rm ln} \hspace{0.1cm} 5+ 1.151+ 2.030-1.417\hspace{0.15cm}\underline{=0.155\,{\rm Np }}\hspace{0.05cm}.$$

This is equivalent to   $0.155\ {\rm Np} \cdot 8.686 \ {\rm dB/Np} \hspace{0.15cm} \underline{= 1.346 \ {\rm dB}}$.


(4)  The following holds for the phase function according to the description in the theory section due to  $K > 0$ :

$$b(f ={2}/\pi) = \phi_{\rm x1} + \phi_{\rm x2}-\phi_{\rm o}\hspace{0.05cm},$$
$$\phi_{\rm x1} ={\rm arctan}\hspace{0.15cm}(1/3) =18.4^\circ\hspace{0.05cm}, \hspace{0.5cm}\phi_{\rm x2} = {\rm arctan}\hspace{0.15cm}(7/3) =66.8^\circ\hspace{0.05cm},\hspace{0.5cm} \phi_{\rm o} = {\rm arctan}\hspace{0.15cm}(-1/4) =180^\circ - 76^\circ = 104^\circ $$
$$ \Rightarrow \hspace{0.3cm}b(f ={2}/\pi) =18.4^\circ + 66.8^\circ - 104^\circ \hspace{0.15cm} \underline{= -18.8^\circ}\hspace{0.05cm}.$$