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The 0.6V offset of a BJT emitter follower is annoying, but you can offset it again with the opposite type of BJT. In that way, the output voltage will be the same as the input voltage.
- NPN BJT emitter follower has an output voltage that is 0.6V lower than the signal it is given.
- PNP BJT emitter follower has an output voltage that is 0.6V higher than the signal it is given.
The PNP BJT output can be used as the NPN BJT input. That is what is shown in the diagram. The PNP Emitter output is 0.6V higher than signal at the PNP Base voltage. That Vin + 0.6V is what the voltage NPN Base gets. So the NPN BJT will drop that voltage by 0.6V at it’s emitter. Giving you Vin +0.6V – 0.6V = Vin.
Keep in mind though, that with this setup, you can output all the way down to 0V, but not all the way to the positive supply (Vcc). If using +5V for Vcc (as shown in diagram), then you can expect a maximum of 4.4V at the output.
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