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According to what I read the circuit above is the schema of emitter repeater, it is used between two amplifiers to connect them and it's gain A = 1; it does not amplify the signal. But I want to get a better understanding of it

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    \$\begingroup\$ It's called "emitter follower" and its voltage gain is 0 dB, yes, but the current gain can be substantial. \$\endgroup\$ – Sredni Vashtar Jan 9 at 9:54
  • \$\begingroup\$ Gain of 0 would be "no output at all." A gain of 1 or a gain of 0dB is what you mean. \$\endgroup\$ – JRE Jan 9 at 9:56
  • \$\begingroup\$ thank you very much sir, I was having trouble finding it's correct name \$\endgroup\$ – Pərviz Piri Jan 9 at 9:56
  • \$\begingroup\$ @PərvizPiri It's main value is in increasing the current compliance (current gain.) \$\endgroup\$ – jonk Jan 9 at 11:18
  • \$\begingroup\$ It's a bad translation of "emitter follower". \$\endgroup\$ – user_1818839 Jan 9 at 14:23

You can learn more about it by using the correct term of "emitter follower".

It also has a gain of 1 which means it just buffer the signal. Gain of 0 means it will output nothing.

In real life the gain is almost 1, but it will be slightly less than 1.


This Common Collector or Emitter Follower classic circuit has an output impedance that reduces the source impedance by hFE, the current gain of the transistor.

For large signal swing Ry must not be less than Re so as the AC current does not starve the emitter of DC current.

  • \$\begingroup\$ A well overlooked problem with capacitor coupled emitter followers, thanks for pointing it out! \$\endgroup\$ – niko20 Jan 9 at 22:52

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