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A common-emitter amplifier has a transistor with β = 90, a collector resistor of 4.5 kΩ and an…

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A common-emitter amplifier has a transistor with $\beta = 90$ , a collector resistor of $4.5\ \text{k}\Omega$ and an input resistance of $1.5\ \text{k}\Omega$ . A signal of amplitude $8.0$ mV is applied. Find the size of the voltage gain, the amplitude of the output and the power gain. Say what the phase of the output is compared with the input.

Need a reminder? The key ideaShow

The voltage gain of a common-emitter amplifier is $A_V = -\dfrac{\beta R_C}{r_i}$ , the current gain is $\beta$ and the power gain is $\beta |A_V|$ . The output $V_{CE}$ stays between $0.2$ V (saturation) and $V_{CC}$ (cut-off). A transistor switch saturates when $I_B \ge \dfrac{V_{CC} - 0.2\ \text{V}}{\beta R_C}$ .

The worked solution

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Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.

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