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Chapter 5: Problem 73

a. Sketch the Giacoletto (hybrid \(\pi\) ) model for a common-emitter transistor if \(r_{b}=4 \Omega\), \(C_{m}=5 \mathrm{pF}, C_{u}=1.5 \mathrm{pF}, h_{o e}=18 \mu \mathrm{S}, \beta=120\), and \(r_{e}=14 .\) b. If the applied load is \(1.2 \mathrm{k} \Omega\) and the source resistance is \(250 \Omega\), draw the approximate hybrid \(\pi\) model for the low- and mid- frequency range.

Short Answer

Expert verified
The hybrid pi model for the specified common emitter transistor can be drawn by labeling the base, emitter, and collector currents and voltages along with the resistances, capacitances, and other given parameters. For low and mid-range frequencies, the capacitances can be ignored, and load and source resistances have been added to the base and collector circuits, respectively.

Step by step solution

01

Sketch the Giacoletto Model

Start by labelling a blank common emitter transistor diagram with the given parameters. This involves labeling the base, emitter, and collector voltages. Sketch resistors \(r_{b}\) and \(r_{e}\) along with the current-controlled current source (\(h_{o e}\)). Next, sketch capacitors \(C_{m}\) and \(C_{u}\) on the base and collector circuit respectively. Lastly, include the current gain factor \(\beta\).
02

Draw the low- and mid-range frequency Model

First, draw the hybrid pi model as before. Because we are dealing with low and mid frequencies, the capacitances can be ignored as the impedance they create is very high. We still need to take into consideration \(r_{b}\), \(r_{e}\), \(h_{o e}\) and \(\beta\). In addition, the load and source resistances should now be included. Draw and label the source resistance (attribute it with \(250 \Omega\)) entering the base of the transistor and label the load resistance (attribute it with \(1.2 \mathrm{k} \Omega\)) exiting the collector of the transistor.

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Most popular questions from this chapter

For the common-base configuration of Fig. 18, an ac signal of \(10 \mathrm{mV}\) is applied, resulting in an ac emitter current of \(0.5 \mathrm{~mA}\). If \(\alpha=0.980\), determine: a. \(Z_{i}\) b. \(V_{o}\) if \(R_{L}=1.2 \mathrm{k} \Omega\). c. \(A_{v}=V_{d} / V_{i}\). d. \(Z_{o}\) with \(r_{o}=\infty \Omega\). e. \(A_{i}=I_{o} / I_{i}\) f. \(I_{b}\)

Given the typical values of \(R_{L}=2.2 \mathrm{k} \Omega\) and \(h_{o e}=20 \mu \mathrm{S}\), is it a good approximation to ignore the effects of \(1 / h_{o e}\) on the total load impedance? What is the percentage difference in total loading on the transistor using the following equation? $$ \% \text { difference in total load }=\frac{R_{L}-R_{L} \|\left(1 / h_{o e}\right)}{R_{L}} \times 100 \% $$

The input impedance to a common-emitter transistor amplifier is \(1.2 \mathrm{k} \Omega\) with \(\beta=140\), \(r_{o}=50 \mathrm{k} \Omega\), and \(R_{L}=2.7 \mathrm{k} \Omega\). Determine: a. \(r_{e}\) b. \(I_{b}\) if \(V_{i}=30 \mathrm{mV}\). c. \(I_{c}\). d. \(A_{i}=I_{o} / I_{i}=I_{L} / I_{b}\). e. \(A_{v}=V_{o} / V_{i}\)

If a transistor amplifier has more than one dic source, can the superposition theorem be applied to obtain the response of each dc source and algebraically add the results?

a. Given an Early voltage of \(V_{A}=100 \mathrm{~V}\), determine \(r_{o}\) if \(V_{C E_{e}}=8 \mathrm{~V}\) and \(I_{C_{Q}}=4 \mathrm{~mA}\). b. Using the results of part (a), find the change in \(I_{C}\) for a change in \(V_{C E}\) of \(6 \mathrm{~V}\) at the same \(Q\) -point as part (a).
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