Transconductance Chart

Discussion in 'General Electronics Chat' started by KCHARROIS, Apr 7, 2013.

Jun 29, 2012
292
1
Hello,

I cant make sense of this chart below about transconductance, any clue?

Thanks

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Last edited: Apr 7, 2013
2. patricktoday Member

Feb 12, 2013
157
42
gm is transconductance and the mho unit tells you what to multiply by the voltage in column 1 to get the resultant output current. Capital "G", Gm, represents "large signal" and lowercase "g", gm, represents "small signal." I'm not sure about column 4. It appears to show the percentage mho that will occur at an arbitrary Icq (collector quiescent current)... I notice that each value in column 3 below the 1st cell could be derived from multiplying the 1st cell (0.038) times the "percentage" in column 4.

PackratKing likes this.

Jun 29, 2012
292
1
Ok but I don't get how they got results in column number 3 with just the signal peak voltage?

4. patricktoday Member

Feb 12, 2013
157
42
What type of device or circuit is this for? You didn't provide any context.

Jun 29, 2012
292
1
Its for a colpitts oscillator, I'm reading a book called build your own transistor radio and I;m reading the oscillator chapter formulas like Ic=Is*e^Vbe/0.026 were given.

Jun 29, 2012
292
1
This might help...

If mho equals (below) Ic =

0.037mho 0.962mA
0.034mho 0.884mA
0.036mho 0.676mA

because Ic = mho * 0.026mV

7. patricktoday Member

Feb 12, 2013
157
42
The mho calculation is the inverse of the emitter resistance, so, yes, this sounds correct. To get emitter resistance, we usually calculate 0.026/Ie if Ie is already known... so the mho calculation is 1/(0.026/Ie) (and Ic will be very close to Ie).

Last edited: Apr 7, 2013

Jun 29, 2012
292
1
Ok so I think I figured it out...

If mho for 0.013Vp is 0.037mho then with the formula gm = Icq/0.026

Icq = 0.962 mA//

Now since the graph is referring to 1mA = 0.0384615mho

(0.962mA/1mA)*100 = 96.2

At a signal of 0.013, (0.0384615/100)*96.2 = 0.037//

I guess the graph is referring to 1mA for everything because current changes as input signal increases.