# correction to Biasing calculations

Joined Apr 5, 2012
26
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

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#### Georacer

Joined Nov 25, 2009
5,182
Can you provide the link to the e-book chapter this is from?

Joined Aug 17, 2013
858
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":

Joined Aug 17, 2013
858
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."

Last edited:

Joined Aug 17, 2013
858
Also here:
"The value of internal resistance RE is a function of emitter current IE, Table below. "
"RE" should be "REE".

#### Georacer

Joined Nov 25, 2009
5,182
Also here:
"The value of internal resistance RE is a function of emitter current IE, Table below. "
"RE" should be "REE".
Correct, and the "Table below", isn't even a table.

Joined Aug 17, 2013
858
Correct, and the "Table below", isn't even a table.
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.

Joined Aug 17, 2013
858
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"...
Thus, for the common-emitter circuit Rin is
Rin = βREE/IE
... and then further down without it...
Rin = βREE = 100(26) = 2600Ω
Shouldn't it be always "Rin = βREE", without the "/IE"?

#### LvW

Joined Jun 13, 2013
1,300
Also here:
"The value of internal resistance RE is a function of emitter current IE, Table below. "
"RE" should be "REE".
I dont 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:
Dont 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 Ohms law.
According to my experience, some beginners indeed were following this false approach.

Last edited:

Joined Aug 17, 2013
858
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.

#### LvW

Joined Jun 13, 2013
1,300
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.

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 whats going on within the BJT?

#### Dcrunkilton

Joined Jul 31, 2004
422
Last edited:

#### Dcrunkilton

Joined Jul 31, 2004
422
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":

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

Credited to adam555 in the Contributors List.

Dennis

#### Dcrunkilton

Joined Jul 31, 2004
422
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."
emitter resistor replaced by base resistor as proposed at ibiblio

Dennis

#### Dcrunkilton

Joined Jul 31, 2004
422
Also here:
"The value of internal resistance RE is a function of emitter current IE, Table below. "
"RE" should be "REE".
Changed to REE as proposed at ibiblio.org

Thanks,

Dennis

#### Dcrunkilton

Joined Jul 31, 2004
422
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.
Added a bigspace tag to the source at ibiblio.org to correct this.

Dennis

#### Dcrunkilton

Joined Jul 31, 2004
422
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"?
I deleted the "/IE" from the line in the copy at ibiblio.org .

Credited to adam555 in the Contributors list

Thanks,

Dennis

#### Dcrunkilton

Joined Jul 31, 2004
422
I dont 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:
Dont 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.

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.