Series bandpass filter graph

  • Thread starter so_gr_lo
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  • #1
so_gr_lo
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10
Homework Statement:
I am plotting Vout/Vin against frequency for a RLC series bandpass filter, where Vout is across the resistor. The resulting graph has max Vout/Vin of about 1.5, the max is supposed to be 1 in a bandpass filter. The Vout/Vin values are experimental, could a max Vout/Vin of 1.5 occur in an experiment? And what could be the reason for this?
Relevant Equations:
Vin/Vout = R / (R+wL -1/wc) , where w = omega
this is the circuit
1648543482474.png


this is the theoretical graph

1648543876109.png
 

Answers and Replies

  • #2
BvU
Science Advisor
Homework Helper
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Hi,

Your relevant equation is an equation with complex quantities on both sides.
(I think you switched in and out subscripts ?)

What you measure is most likely the real ratio of two amplitudes. As plotted in the theoretical graph.
For the complex impedance of the RLC series we have $$Z^2 = R^2 + \left (\omega L - {1\over \omega C}\right )^2 $$ with a minimum ##Z=R## (and ##V_{out}/V_{in}=1## ).

A measured ratio can deviate if the measurement equipment influences the circuit. So you have to check values of components and equipment.

##\ ##
 
  • #3
so_gr_lo
67
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So what equation could you use to plot theoretical values of Vout / Vin ?
 
  • #4
DaveE
Science Advisor
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So what equation could you use to plot theoretical values of Vout / Vin ?
Are you familiar with complex number arithmetic? With the representation of impedance using complex numbers? I think that is necessary to understand this without a tremendous amount of work.

Do you know about simple circuit analysis, like voltage dividers?

This is important information for us to know to help appropriately.
 
  • #5
DaveE
Science Advisor
Gold Member
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Khan Academy has some really good tutorials on these subjects.
 

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