A certain common-emitter amplifier has a voltage gain of 100. If the emitter byp

Question

A certain common-emitter amplifier has a voltage gain of 100. If the emitter bypass capacitor is removed. (a) The circuit will become unstable (b) the voltage gain will decrease (c) The voltage gain will increase (d) the Q-point will shift For a common emitter amplifier, R_C = 2.0 K Ohm, R_E = 390 Ohm, re = 15 Ohm and beta = 75. Assuming that R_E is completely bypassed at the operating frequency, the voltage gain is (a) 133 (b) 2.56 (c) 5.12 (d) 75 For the common-base bias configuration, there is a _____ phase shift between the input and output signals. (a) 0 degree (b) 45 degree (c) 90 degree (d) 180 degree The _____ configuration is frequently used for impedance matching. (a) fixed bias (b) voltage-divider bias (c) emitter-follower (d) collector feedback.

Explanation / Answer

4.   The voltage gain will decrease.

(emitter bypass capacitor help to reduce negative feedback,on removal of this capacitor negative feedback will increase which decrease the voltage gain)

5. Gain = Rc/re = 2000/15 = 133

6.   zero degree (00 )

(In common base bias configuration,input is applied at emitter and output is sensed at the collector. so, when we apply apply a positive signal to the emitter. This will cause emitter current to increase. As emitter and collector current are almost equal, the collector current also increases. This collector current passes through the collector resistor. A higher collector current causes a larger drop across the collector resistor. And, output is sensed across this collector resistor, so an increase in the input (at the emitter) causes an increase at the output (across the collector resistor) so we conclude that input and output are in phase (no phase reversal).

7. Emitter-follower.

( It used because of the very high input impedance, in the region of hundreds of thousands of Ohms while having a relatively low output impedance. The common-collector is also used.)

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