Electronics > Beginners
Common Emitter BJT amp phase
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TheBaconWizard:
I've been looking at common emitter BJT amplifiers and I get the principle in general..  I want voltage amplification hence this choice, and in this case it only needs to be on or off, so saturation-mode.

However, all the tutorials I've seen so far tell me that the same waveform is produced whether I use NPN or PNP. It seems to me that they should be the precise inverse of each other? What am I missing?

In fact..  if indeed they DO have exactly the same result, how WOULD I produce a signal that is exactly 180deg out of phase compared with these simple amplifiers?

Many thanks
David Hess:
Common emitter, aka shunt feedback amplifiers, invert the input signal whether NPN or PNP.  If you want a non-inverted signal, then you can use a common base or common collector NPN or PNP, use two common emitter amplifiers in series, or maybe add a transformer.
TheBaconWizard:
Many thanks
vk6zgo:

--- Quote from: David Hess on June 19, 2018, 09:17:03 am ---Common emitter, aka shunt feedback amplifiers, invert the input signal whether NPN or PNP.  If you want a non-inverted signal, then you can use a common base or common collector NPN or PNP, use two common emitter amplifiers in series, or maybe add a transformer.

--- End quote ---

Actually, you would use two CE stages in cascade .
Two transistors in series is a very different  circuit configuration.
David Hess:

--- Quote from: vk6zgo on June 19, 2018, 11:20:22 am ---
--- Quote from: David Hess on June 19, 2018, 09:17:03 am ---Common emitter, aka shunt feedback amplifiers, invert the input signal whether NPN or PNP.  If you want a non-inverted signal, then you can use a common base or common collector NPN or PNP, use two common emitter amplifiers in series, or maybe add a transformer.
--- End quote ---

Actually, you would use two CE stages in cascade.

Two transistors in series is a very different  circuit configuration.
--- End quote ---

Thanks.  Learning or being reminded of something like this is why I participate.

A differential pair can also be used and it produces both outputs.
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