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KCC's quizzes AQQ235 about a bipolar common emitter amplifier - a kind proposal from our colleague Martin Walker

Apologize for our non-technical audience since this quiz is more for our FAEs...

A kind proposal from our colleague Martin Walker, ADI Product Marketing Engineer, UK:

Most of our electronic engineers have seen this sort of circuit in their first year study time using a bipolar transistor in its 3 famous basic configurations: common emitter, common collector and common base.

Here above is a common emitter configuration.

Conditions:

  • Vcc = 6V
  • Vout = 3V
  • Tc = 25°C

Q1 is a BJT NPN with current gain β of several hundreds.

RB1 and RB2 are large compared to RC and RS

 Questions :

  1. Is there enough information to work out the gain of this circuit?
  2. If so, what is the voltage gain of the circuit?
  3. Is it a good amplifier?
  4. If not, what would you do to mitigate for its limitations?

Again, many thanks Martin!



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[edited by: emassa at 2:19 PM (GMT -4) on 22 May 2023]
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  • Hi, according to me there are not sufficient information to calculate the gain. The equivalent small signal model shows that the gain is dependent by parameters like output resistance hoe and hfe. (low freq. range)

    There is not any feedback. Nor signal neither DC feedback. The bias condition is affected by temperature. Adding an emitter resistor will allow to fix the gain to RC/RE and to have feedback to the bias point fixing the bias current. 

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  • Hi, according to me there are not sufficient information to calculate the gain. The equivalent small signal model shows that the gain is dependent by parameters like output resistance hoe and hfe. (low freq. range)

    There is not any feedback. Nor signal neither DC feedback. The bias condition is affected by temperature. Adding an emitter resistor will allow to fix the gain to RC/RE and to have feedback to the bias point fixing the bias current. 

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