transistor amplification

1. transistor amplification

why does a common emitter bjt after amplification inverts the signal in comparison 2 other configurations. Trying to understand the principle

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2. Re: transistor amplification

In common emitter circuits an increase in Base voltage causes a decrease in Vout and a decrease in Base voltage produces an increase in Vout. In other words the output signal is 180o out-of-phase with the input signal. The Voltage Gain of the common emitter amplifier is equal to the ratio of the change in the input voltage to the change in the amplifiers output voltage. Then ΔVL is Vout and ΔVB is Vin. But voltage gain is also equal to the ratio of the signal resistance in the Collector to the signal resistance in the Emitter or:
Vout/Vin = ΔVL/ΔVB = -(RL/RE)

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3. Re: transistor amplification

Originally Posted by Yordan_Kovachev
In common emitter circuits an increase in Base voltage causes a decrease in Vout and a decrease in Base voltage produces an increase in Vout.
I`ve got the impression that Andrew would like to know WHY there is a phase inversion.