BJT Common Emitter Amplifier

Thread Starter

The_Cook

Joined May 29, 2014
48
upload_2014-10-20_22-18-20.png
The values are :
  • Vs = 10 mV
  • Rb = 100 Kohms
  • Rc = 2 Kohms
  • Rl = 4 kohms
  • gm = 170 mA/V
  • r(pi) = 580 ohms
  • Rs = 50 ohms
For this circuit I have to draw (a) draw a small signal amplifier equivalent circuit and (b) find the mid-band voltage gain for given Vs

I would appreciate if someone helps me get started with the equivalent circuit.

Thanks!
 

crutschow

Joined Mar 14, 2008
34,285
That circuit will not amplify AC as it is not biased. The output will basically be a half-wave rectified signal. Here's an example of a transistor biased to amplify an AC signal.
 

MikeML

Joined Oct 2, 2009
5,444
However, as Zapper pointed out, the hybrid PI model cannot be used to model the original schematic because the hybrid pi model assumes that the biasing has already been done.
 

Thread Starter

The_Cook

Joined May 29, 2014
48
Yeah I understand that the Hybrid Pi model cannot be used. But if we assumed that it is biased how would you go about solving the problem? I don't know if my professor made a mistake when he wrote it or not?
 

b1u3sf4n09

Joined May 23, 2014
113
With the given information, vbe = 0, therefore gain = 0. Not only is the amplifier not on, but Vs is a DC voltage, which will have some issues bypassing the coupling capacitor. Is there a given frequency for Vs?
 

crutschow

Joined Mar 14, 2008
34,285
Yeah I understand that the Hybrid Pi model cannot be used. But if we assumed that it is biased how would you go about solving the problem? I don't know if my professor made a mistake when he wrote it or not?
He made a mistake if he intended the amplifier to have any gain above zero. :rolleyes:
 
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