correction to Biasing calculations

Discussion in 'Feedback and Suggestions' started by mnada, Sep 2, 2013.

  1. mnada

    Thread Starter New Member

    Apr 5, 2012
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    Dears, I found the following in this page In the attached file, which I need your confirmation if what I think is true or not. I believe the marked should be RE
     
  2. Georacer

    Moderator

    Nov 25, 2009
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    Can you provide the link to the e-book chapter this is from?
     
  3. mnada

    Thread Starter New Member

    Apr 5, 2012
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  4. adam555

    Active Member

    Aug 17, 2013
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    Not sure you might also want to correct a small typo I found in this chapter; it's nothing important. In the second line of the Emitter-bias formulas the first "β" is written with a lowercase "b":

    [​IMG]
     
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  5. adam555

    Active Member

    Aug 17, 2013
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    I think I found 2 more in that same chapter....

    The first is in this paragraph:
    "How can we improve the performance of emitter-bias? Either increase the emitter resistor RB or decrease the base-bias supply VBB or both. As an example, we double the emitter resistor to the nearest standard value of 910Ω."
    In which I think "RB" should be "RE"

    And in this paragraph:
    "As an exercise, rework the emitter-bias example with the base resistor reverted back to 470Ω, and the base-bias supply reduced to 1.5V."
    I think it should read "emitter resistor" instead of "base resistor".
     
    Last edited: Nov 15, 2013
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  6. adam555

    Active Member

    Aug 17, 2013
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    Also here:
    "The value of internal resistance RE is a function of emitter current IE, Table below. "
    "RE" should be "REE".
     
  7. Georacer

    Moderator

    Nov 25, 2009
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    Correct, and the "Table below", isn't even a table.
     
  8. adam555

    Active Member

    Aug 17, 2013
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    I'm not trying to be picky -just helping-, but now that you mention the tables, when I reached the next one at a first glance I got the impression that "Bypass Capacitor for RE" was the table caption instead of the title for the next section; as it's right under it without any separation line.
     
  9. adam555

    Active Member

    Aug 17, 2013
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    I think I found a minor mistake in the "Amplifier impedance" chapter; though maybe I'm wrong.

    I'm not sure if this formula is right. You wrote it first with the "/IE"...
    ... and then further down without it...
    Shouldn't it be always "Rin = βREE", without the "/IE"?
     
  10. LvW

    Active Member

    Jun 13, 2013
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    I don`t like at all the usage of REE.
    I know what it means (it is 1/gm=Vt/Ic), however there is one general and important rule:
    Don`t mix ohmic (static) resistances with dynamic (differential) resistances.
    This of extreme importance for understanding all circuits involving non-linear parts (diodes, transistors).
    Thus, all differential parameters should carry SMALL letters and we always should write rEE.

    EDIT: Using this unfortunate symbol REE the gain of an emitter stage is
    G=-Rc/(REE+Re)
    Thus, it looks as the gain is simply determined by ohmc resistors following Ohm`s law.
    According to my experience, some beginners indeed were following this false approach.



     
    Last edited: Nov 19, 2013
  11. adam555

    Active Member

    Aug 17, 2013
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    Yes, that happened to me: the first time I came across "REE" I had no idea it was a dynamic resistance. But I already knew that when I read the "Biasing Calculations" chapter.
     
  12. LvW

    Active Member

    Jun 13, 2013
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    May I add another point?

    Without emitter resistor Re the gain of the circuit (which is a voltage-controlled current source with a load Rc) is

    G=-gm*Rc.

    To me, usage of a transconductance gm is straight-forward and logical because this parameter describes the input-output transfer charcteristic of the BJT (slope of the Ic=f(Vbe) curve).
    And therefore my question: Is there any good reason NOT to use gm but, instead, a symbol r,ee (or even R,ee) ? Does this make any sense or does it help to understand what`s going on within the BJT?
     
  13. Dcrunkilton

    E-book Co-ordinator

    Jul 31, 2004
    416
    11
    Thanks mnada for the nice attachment, Which made it easier to make the change at ibiblio.

    Entered RE 3-places as pointed out in the nice attachment.

    Credited to mnada in the Contribbutors List

    Dennis
     
    Last edited: Feb 2, 2014
  14. Dcrunkilton

    E-book Co-ordinator

    Jul 31, 2004
    416
    11

    Letter b changed to symbol Beta in image 03488.png at ibiblio.org

    Credited to adam555 in the Contributors List.

    Thanks adam555,

    Dennis
     
  15. Dcrunkilton

    E-book Co-ordinator

    Jul 31, 2004
    416
    11
    emitter resistor replaced by base resistor as proposed at ibiblio

    Credited to adam555

    Dennis
     
  16. Dcrunkilton

    E-book Co-ordinator

    Jul 31, 2004
    416
    11
    Changed to REE as proposed at ibiblio.org

    Credited to adam555

    Thanks,

    Dennis
     
  17. Dcrunkilton

    E-book Co-ordinator

    Jul 31, 2004
    416
    11
    Added a bigspace tag to the source at ibiblio.org to correct this.

    Credited to adam555

    Dennis
     
  18. Dcrunkilton

    E-book Co-ordinator

    Jul 31, 2004
    416
    11
    I deleted the "/IE" from the line in the copy at ibiblio.org .

    Credited to adam555 in the Contributors list

    Thanks,

    Dennis
     
  19. Dcrunkilton

    E-book Co-ordinator

    Jul 31, 2004
    416
    11


    I have changed 22 instances of REE to rEE in the text and more in the images : 03489.eps 03494.eps 03495.eps 03497.eps 13062.eps , read .png for .eps on AAC.

    I won't touch gain G for now.

    Credited to LvW in the Contributors List.

    Thanks for your input,

    Dennis
     
  20. adam555

    Active Member

    Aug 17, 2013
    858
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