Can you do a schema of it ? I don't really understand

The transconductance is proportional to the DC bias collector current, and the voltage gain equals the transconductance times the collector resistance value.
Note that this gain is not determined by the transistor current-gain (Beta or Hfe) and is basically independent of that.

Below is the LTspice sim of a simple, single-stage circuit showing the voltage gain (180.5), which is close to that calculated from the above equation:
(Of course the real circuit would be biased with resistors, not an emitter current source).

(Using two direct coupled stages, my sim shows an output of 2Vpp for a 100µVpp input can be readily obtained.)

 

Your simple amplifier produces severe distortion (without clipping) at high output levels because it is missing some negative feedback that reduces voltage gain and reduces distortion. The voltage gain of the transistors is too high and instead of your RB22 shorting away some of the gain, an unbypassed part of the emitter resistors reduces the gain and reduces the distortion.

Here is a simulation of the severe distortion at high output level (without clipping) of the output transistor:

 

Distortion at high output isn't much of a problem when the TS is looking for a voltage gain of 1000 on a signal with an amplitude of 2 µV.

 

An input signal level of only 2uV at 1kHz is useless for anything. Maybe an ECG (for heartbeats) or an EEG (for brainwaves) are used at much lower frequencies.

 

An input signal level of only 2uV at 1kHz is useless for anything. Maybe an ECG (for heartbeats) or an EEG (for brainwaves) are used at much lower frequencies.

We don't know what the source of the signal is, only what the TS is saying they have been asked to design for.

I used to work where the signals we were interested in were in the nanovolt range, so I'm not going to assert that a 2 uV signal at 1 kHz is useless.

Now, whether this amplifier is sufficiently low noise to work with such signals is a different matter, but that may well be part of what they want the TS to discover and/or deal with next.

 

We don't know what the source of the signal is, only what the TS is saying they have been asked to design for.

I used to work where the signals we were interested in were in the nanovolt range, so I'm not going to assert that a 2 uV signal at 1 kHz is useless.

Now, whether this amplifier is sufficiently low noise to work with such signals is a different matter, but that may well be part of what they want the TS to discover and/or deal with next.

I set the input at 2uV arbitrarily, the only fact is that at 1khz, i should have 1000 of gain, and i must demonstrate it by calculations too, there is no APPLICATIONS for this amplifier, this is just an exercice.

 

Hi Phil,
Choosing a Vinput of 2uVolt is not a good decision, I would suggest say 1mVolt, this would give a 1Volt output.
ie: 1mV * 1000 = 1Volt

E

 

Hi Phil,
Choosing a Vinput of 2uVolt is not a good decision, I would suggest say 1mVolt, this would give a 1Volt output.
ie: 1mV * 1000 = 1Volt

E

Thanks for the tips, now, i just need to epxress the gain from this circuit ! that's the only thing i want....

 

Thanks for the tips, now, i just need to epxress the gain from this circuit ! that's the only thing i want....

You have been given the formula, what is stopping you?

 

You have been given the formula, what is stopping you?

I don't see any formula like Vout/ Vin = [...] in AC. The expression of Vin is pretty simple, the expression of Vout is not. Beacause it's involving RC2, RC1 and RB22. This is this expression that i can't find by calculations

 

I don't see any formula like Vout/ Vin = [...] in AC. The expression of Vin is pretty simple, the expression of Vout is not. Beacause it's involving RC2, RC1 and RB22. This is this expression that i can't find by calculations

So you need to analyze the circuit.

Don't look for some equation from on high to be given to you. Analyze the circuit.

How you go about the analysis depends on how far you have gotten in your circuit courses.

Have you covered small-signal models of transistors?

 

So you need to analyze the circuit.

Don't look for some equation from on high to be given to you. Analyze the circuit.

How you go about the analysis depends on how far you have gotten in your circuit courses.

Have you covered small-signal models of transistors?

I found alone the solution of my own question.

The answer was Total voltage gain = voltage gain of Q1 * voltage gain of Q2 . It was AS ESAY AS THAT

thanks

 

Except that transistors do not have a voltage gain. A CE or CB amplifier circuit does.

That formula applies to a two stage amplifier, which you said you could not use, if I remember correctly. And it is not correct either, there are losses in the output impedance of the first stage and the input impedance of the second, which firm a voltage divider.

 

With an input that is only 2uV, the output will be full of noise.

 

I found alone the solution of my own question.

The answer was Total voltage gain = voltage gain of Q1 * voltage gain of Q2 . It was AS ESAY AS THAT

thanks

So what is the "voltage gain of Q1"? What is the "voltage gain of Q2"?

Are you sure that the "voltage gain of Q1" is not affected by the presence of Q2?