# PSPICE HOMEWORK help voltage gain,..

Discussion in 'Homework Help' started by Judas543, Feb 4, 2010.

1. ### Judas543 Thread Starter Member

Jan 26, 2010
60
0
I think i have all the info...
So my question is how to calculate the voltage gain for the amplifier? and the ratio of the voltage amplitudes? Is their a formula or just by reading the graph..

Schematic + Problem:

My Graph:

Last edited: Feb 4, 2010
2. ### Audioguru New Member

Dec 20, 2007
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896
The output on the graph is 290mV peak but you don't know and the graph does not show if the input is 5mV RMS, 5mV peak or 5mV p-p.

It is not difficult to calculate the voltage gain.

3. ### Judas543 Thread Starter Member

Jan 26, 2010
60
0
i really appreciate the help, but one i know the input, what can i do then? And how do do iget the input or know it?

4. ### Audioguru New Member

Dec 20, 2007
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896
Don't you know how to calculate the voltage gain? It is simple.

If you can magnify the input signal on the graph then you can measure the input accurately. Then you can see the voltage gain of the circuit.

5. ### Judas543 Thread Starter Member

Jan 26, 2010
60
0
and what would be the ratio of the voltage amplitudes?

6. ### Audioguru New Member

Dec 20, 2007
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896
The ratio of the voltage amplitudes is shown on the graph and can be simply calculated.

7. ### Judas543 Thread Starter Member

Jan 26, 2010
60
0
sorry for being stupid, but how do i calculate it

8. ### Audioguru New Member

Dec 20, 2007
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896
The voltage gain of a transistor is the collector total R divided by the emitter total R.
The collector total R is the collector resistor in parallel with the load resistor.
The emitter total R is the emitter resistor in series with the internal emitter resistance of the transistor.
The internal emitter resistance is 0.026 divided by the emitter current.
This assumes that the capacitors in the circuit have enough value that they are not performing like highpass filters which reduces the low frequency voltage gain.

9. ### Judas543 Thread Starter Member

Jan 26, 2010
60
0
thank you ! Sorry for the trouble...

10. ### Audioguru New Member

Dec 20, 2007
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896
The next questions will be, "How do you calculate the emitter current? What are the resistors for?"

11. ### Nanophotonics Active Member

Apr 2, 2009
365
3
Sorry for the intrusion, but how low is low? Aren't AC coupled caps supposed to behave as shorts at high frequency?

12. ### Audioguru New Member

Dec 20, 2007
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896
You can calculate the frequencies where the capacitors each reduce the gain by -3dB.