HELP Single Stage BJT Common Emitter Amplifier resistor cal

bjt common emitter amplifier

Hello.. can anyone help me out to calculate the value of resistors R1, R2, Rc and RE please?

The values should be such as the out gain is between 10dB to 20dB

The transistor used in this circuit is bc547 and the load resistor is a fixed one of 10k.
Below is the circuit:

**broken link removed**

Thanks

single stage bjt amplifier

Without any calculations one can see that the gain always will be < 0 dB because of the emitter resistance. Or did you forget to bridge this resistor with a capacitor ?

single stage common emitter amplifier

No.. with the capacitor the gain will be too high..

hundreds..

and i want the gain to be only between 10-20dB.

Or may be should decrease the values of ths resistors.. but i dnt know what values to put..


thats the help i need..

thx..

Added after 22 minutes:

Am i rite?

common emitter

The basic knowledge for designing an amplifier is an appropriate gain formula.
Do you know it ?
Otherwise, it makes no sense to give you just only the parts values.

common emitter amplifier

yes voltage gain =Vo/Vin = -Rc/Re

If capacitor not present it will be Rc/(Re+RE)

Am i rite?

ce amplifier singlestage

NiCeMaN said:

yes voltage gain =Vo/Vin = -Rc/Re
If capacitor not present it will be Rc/(Re+RE)
Am i rite?

Click to expand...

What is Re ???

OK, independent on this question and because - up to now - nobody gave you an answer, here are some background information to you:

1.) The formula Rc/(Re+RE) is a rather good approximation (without capacitor acroos RE) if Re=1/gm with gm=transconductance of the BJT. And in most cases you can neglect 1/gm<<RE.
2.) However, if there is a load, you have to replace RC by RC||Rload
3.) But for your values of course: Vo/Vin=gain<1.
4.) Thus, you have to reduce RE considerably.
5.) As a consequence, you have to recalculate R1 and R2
6.) Recommendation for one possible set of values (out of 1000 alternatives):
6.1) Choose Rc=5 k and Ic=1mA >>>Rc||Rload=3.33 k
6.2) Take RE= 500 ohms (approximately)
6.3) This leads to a gain of app. 6.6 (16 dB)
6.4) Calculate R2=(0.6+Ic*RE)/Iq with Iq=9*IB=9*Ic/B
with B=current gain of BJT
6.5) Calculate R1=(12-(0.6+Ic*RE))/(10*IB)

Addendum at 17:30 I have corrected an error i line 2 (RE replaced by RC)

bjt formula

Hello,
Finally i calculated these values for R1 & R2 & Rc & RE...

Now the problem i am getting is that my calculated values and measured values is not the same..
Here is my circuit :

**broken link removed**

Using Beta = 110 as on the datasheet :
and also using approximate analysis..
My calculated values are as follows:

Vb=1.597V
Vce= 5.13V
Ic~=IE=0.897mA
Vc=6.03V
Ib=8.08 micro.Amps
Input inpedance = 4791.96 Ohms
Output impedance = 5000 Ohms
Vo=4.44V

Can anyone check my circuit and let me know if its in good working condition?

Thanks in advance...

single stage bjt common emitter amplifier

Your measurement obviuosly doesn't show a plausible steady state bias point, cause the DC voltage at the load resistor would be zero. Thus the collector voltage is possibly also incorrect.

In real life or in a appropriate performed simulation, the collector voltage should be around 8 V for an unloaded amplifier and somewhat lower with the 5 k load for maximum undistorted output voltage. The shown dimensioning is at least near to this operation point.

calculate the gm formula of a bjt

On the other two websites, people say that the simulation software has C2 shorted so the collector DC voltage is half what it should be.