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© François Le Coat
©Karl Samyn
Last modified :
09 mar 1998
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5. The curves of Bode
a. System theory
1. Basic knowledge
2. Harmonic analyse of a linear system
b. Filters with OPAMs
1. OPAM
2. Determination of H(p)
3. Band passage filter
c. More examples (all formulas also available as *.fmu file in directory /bode)
1. Filter using 2 OPAM's
The circuit drawn in fig. 4.3.1 gives this for H(p) :
![[formula example 1]](../images/formulas/form_ex1.gif)
with : T1 = R1C1
T2 = R2C2
R1 = R2 = 1 Mega Ohm
C1 = 1 micro F
C2 = 0.063 micro F
This gives us a "low pass filter" with an amplification of -24 dB.
Try to draw this curves yourself. Both curves are suplied in the /bode directory.
It are /bode/bode_a1.img and /bode/bode_f1.img.
2. Filter from a telephone central
This filter has next H(p) :
![[formula example 2]](../images/formulas/form_ex2.gif)
The files are /bode/bode_a2.img and /bode/bode_f2.img.
3. Special case
Here we have a H(p) that can not be transformed to the form like formula 4.2.1.
![[formula example 3]](../images/formulas/form_ex3.gif)
The general form is this one :
![[formula 4.3.1]](../images/formulas/form_431.gif)
In all the above cases we had dzeta = 1. The curve of the amplitude (/bode/bode_3a.img) we get here, looks similar to the curves from a spring (see mechanics). So does the formula.
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