Question " gain" in this circuit?

[emran]

hello everyone ..

how can i get the " gain" in this circuit? ( in midband)

 

[audioguru]

There is no circuit.

 

[ronsimpson]

10=200k/20k

 

[crutschow]

To elaborate, if you assume the transistor gain is high than the ideal gain is simply the 200k feedback resistor divided by the 20k input resistor as ronsimpson noted. In reality it will be somewhat less due to the finite transistor gain and the base-emitter resistance which is about 26 ohms @ 1ma emitter current interacting with the 225 ohm emitter feedback resistor. A quick simulation gave a gain of 8.34 with a 2N3904 transistor.

 

[ronsimpson]

Question:
Assuming this is home work.
Does the teacher want the answer of 10 because the feedback is set to 10 OR does the teacher want 8 to 9 because that is what happens in real life?
also
Why the emitter resistor? If the teacher wants the answer "10" then there should not be a emitter resistor. Maybe I am over thinking this.

 

[Jony130]

We can try to use a millers effect and try to establish the approximate value for a voltage gain.
20K/225 = 88V/V ;
So from miller effect we have 200k/88 = 2.2K
And the voltage gain 2.2K/(20K + 2.2K ) * 88 = 8.7 V/V

 

[Ratchit]

Emran,

"how can i get the " gain" in this circuit? ( in midband)"

Which gain, voltage or current?

Ratch

 

[crutschow]

Emran,

"how can i get the " gain" in this circuit? ( in midband)"

Which gain, voltage or current?

Ratch

The input is Vsig and the output is labeled Vo. What would be the utility of calculating the current gain of this single transistor CE stage which is obviously a voltage amplifier?

 

[audioguru]

I see no schematic in this thread.
What are you guys talking about?

 

[crutschow]

I see no schematic in this thread.
What are you guys talking about?

His first post shows a schematic. What browser are you using?

 

[Willen]

I see no schematic in this thread.
What are you guys talking about?

hehehe Yes, there is a single transistor amplifier circuit I am seeing.

Also, few days ago you were saying "I downloaded Java runtime and installed but I cannot open the compressor software". I simply installed java runtime (I had old verson 6.3 i guessed) on windows 7. And opened simply the software. But It didn't detect INPUT Audio Driver. Because I didn't installed extra audio driver software there in Windows 7 (there is built-in audio driver only). But I installed Realtek driver in Windows XP, Installed Java Runtime and opened the Compressor software. All were working but I was unable to hear audio deeply to find that it was working or doing nothing. I never noticed about compressor software so.

May be something wrong there in PC?

 

[ericgibbs]

I see no schematic in this thread.
What are you guys talking about?

hi agu,
Try this copy of the OP's cct.

Happy Xmas.
E

 

[audioguru]

Eric,
Thanks for posting the schematic.

I am using Internet Explorer 11 and there is no schematic and no link to a schematic in the first post.
Lately the thumbnails also are blank but when I click on one I see a normal big schematic.

 

[Ratchit]

The input is Vsig and the output is labeled Vo. What would be the utility of calculating the current gain of this single transistor CE stage which is obviously a voltage amplifier?

This is a homework exercise problem and not a designated voltage amplifier. Often problems do ask for both the voltage and current gain. The OP should have been more specific about which gain he wanted, and if voltage gain, he should have specified if he wanted gain referenced at Vsig or Vb, after the 20k source resistance.

Ratch

 

[MrAl]

Hi,

I also interpreted this question to mean a voltage gain because it appears to be set up for that...an AC voltage amplifier.

Using a model of the transistor as a current controlled current source with a constant voltage base emitter diode, i found the following equations using nodal analysis:

Vc=(R2*(R1*(V4+I1*R4)+Rin*(V4+I1*R4)-Vin*B*R4+Vd*B*R4)+R1*(Rin*(V4+I1*R4)+Vd*(B+1)*R4)+Rin*Vin*R4)/(R1*((B+1)*R4+Rin)+Rin*R4+(R1+Rin)*R2)

Vb=(R1*(Rin*(V4+I1*R4)+Vd*(B+1)*R4)+Rin*Vin*R4+(Vd*R1+Rin*Vin)*R2)/(R1*((B+1)*R4+Rin)+Rin*R4+(R1+Rin)*R2)

where
V4 is the collector voltage with zero input signal,
Rin is the transistor input resistance in series with the base emitter diode,
I1 is the 1ma current source,
B is the beta of the transistor,
R1 is the input 20k resistor,
R2 is the 200k resistor,
R3 is the 225 Ohm resistor,
R4 is the 20k load resistor,
Vd is the base emitter diode drop (which can be non linear if needed),
and assuming the two capacitors have zero impedance at the operating frequency.

Using this formula i found the voltage gain to be 7.33, but my guess was higher around 8 due to the 20k on the input and 200k feedback resistor, and the fact that the 225 ohm resistor also provides some negative feedback. That was also using a transistor with a gain of 49, and the transistor was biased pretty hard for this circuit, and Vd was held constant for simplicity. I suspect it could be higher with a different bias too.