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Old 26th November 2013, 12:18 PM   #1
Boscoe is offline Boscoe  United Kingdom
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Default Calculatin VAS gain with CCS

So if we have a regular vas stage with one gain transistor loaded a constant current source how is the voltage gain of the stage calculated?

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Boscoe
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Old 26th November 2013, 12:57 PM   #2
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Well the gain of a common emitter output stage is basically Rc/Re. You need to know the effective impedance of the CCS then it's an easy sum. If you have no physical emitter resistor then it comes down to the value of the intrinsic "little Re" as our lecturer used to call it, of the BJT.
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Old 26th November 2013, 01:10 PM   #3
sajti is offline sajti  Hungary
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Quote:
Originally Posted by Boscoe View Post
So if we have a regular vas stage with one gain transistor loaded a constant current source how is the voltage gain of the stage calculated?

Thanks
Boscoe
That is almost impossible, if the load is only the output EF. So the gain depended by the input impedance of the EF, divided by the total emitter resistance. But the input impedance is depended by the load, the output current, the temperature. So it's not easy to predict.
You apply fixed resistors from the VAS output to the ground, and if this resistor is small enough (1/10 of the worst case input impedance of the output EF) it will depend the gain.

Sajti
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