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  1. #1
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    capacitor cutoff frequency

    hi there, please tell me how to determine the bandwidth from an amplifier circuit? for example in common emitter circuit (with voltage divider bias)? how to determine the high and low cut off frequency in the frequency response? is it we should use the miller theory? please tell me.. thank you.. :)

    •   Alt7th November 2005, 09:55

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    bypass capacitor frequency

    There is some good book that will help you fast and quick: Malvino -Electronic Principles:

    The lower critical frequency is caused by the coupling and bypass capacitors.

    The high critical frequency is caused by the transistor and stray wiring capacitances. (So for this one you have to use Miller's theorem.

    See also attached file!

    I hope this helps you.



    •   Alt7th November 2005, 10:12

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    capacitor cutoff

    thank you for the fast reply.. :)

    yes.. i have read the malvino - electronic principles but it's translated into my language, not the english version, i don't have the english version, i can't understand what the translater say in my book, there are a lot of strange words and it's impede me to understand about it ..

    sorry, where is the file?? and from what i read in the book is, for determine the high and low cut off frequency, we should analyze from Cin, Cout, CE, Cc' and also Cstray, right? for the determine the cut off frequency,Xc should be = R, where R = Zin+Rs, Zin = R1//R2//βr'e, and Rs is the series resistance from the input voltage, Xc = 1/2pifCin, so fin = 1/(2pi(Zin+Rs)Cin), is it right? and for the output frequency (Xc=R), Xc = 1/2pifC, R=Zout, Zout = Rc? C = Cc' + Cstray, so, the fout = 1/(2piZoutC), and i am confused about the bypass capacitor, it said that Ce parallel with emitter resistance, so when Xc = R, R = r'e+(R1//R2//Rs)/β, and therefore f = 1/(2piRCe) <- what frequency is it?

    and from these three frequency, which one is high cut off frequency? and which is the low cut off frequency??

    please give me a brief explanation.. :( thank you very much.. :)

    Added after 13 minutes:

    okay.. sorry.. i've seen the attached file now.. i will try to read it at home.. and will ask again if there are something i don't understand from the attached file.. :p thank you very much.. :)



    •   Alt7th November 2005, 10:57

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    low cutoff frequency

    The low cutoff frequency depends on the couple capacitor.
    The high cutoff frequency depends on the bypass capacitor.



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    capacitor frequency cutoff

    quote:
    The low cutoff frequency depends on the couple capacitor.
    The high cutoff frequency depends on the bypass capacitor.
    -> i am sorry, is it right or wrong??

    after i read the file attached by mobile-it, i thought that the low cut off frequency is depend on coupling capacitor and also bypass capacitor, is it right? the coupling capacitor present a high pass filter, if the frequency is low, the resistance of the coupling capacitor would be high, so it would block the signal in the Cin to go into the transistor to be amplified, and also in the Cout, it would block the amplified signal from transistor to the load, and the bypass capacitor, for example in the Common emitter circuit, it will bypass the emitter to the ground, if the frequency is low, the Xc of bypass capacitor would be high enough to block the signal to the ground, and it will reduce the gain of the amplifier (A = rl/r'e -> if the bypass capacitor can bypass all of the AC signal to the ground, if not, we would need to concern Re in the A, right?), so, in low cut off frequency, it's depend on the coupling and bypass capacitor, and for high cut off frequency, it's depend on Cob and Cbe (can see in the file attached) or the internal capacitance of the transistor, right? and one more question, is it the Cob and Cbe given by the datasheet of every transistor?

    thank you very much.. :)



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    high cutoff frequency

    please , I need this book : Malvino -Electronic Principles



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