** 28 ** Up to now, the emphasis has been on designing a simple amplifier and an emitter follower. This section shows how to “analyze” a circuit that has already been designed. In this case, to “analyze” means to calculate the collector DC voltage (the bias point) and find the AC gain. This procedure is basically the reverse of the design procedure.

Start with the circuit shown in Figure 8.27.

Following are the steps you use to analyze a circuit:

1. Find V_{B} by using the following equation:

2. Find V_{E} by using V_{E} = V_{B }− 0.7 volt.

3. Find I_{C} by using the following equation:

Note that I_{C} = I_{E}.

4. Find V_{R} by using V_{R} = R_{C} × I_{C}.

5. Find V_{C} by using V_{C} = V_{S}2V_{R}. This is the bias point.

6. Find A_{V} by using the following equation:

When you use the second formula, you must find the value of R_{in} (or h_{ie}) on the data sheets for the transistor from the manufacturer.

Use the circuit shown in Figure 8.28 for the following questions. For these questions, use β = 100, R_{in} = 2 kΩ and the values given in the circuit drawing.

Questions

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