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Chapter 12. Power Amplifiers > General Considerations

12.1. General Considerations

As the first step in our study, we consider a transmitter delivering 1 W (+30 dBm) of power to a 50-Ω antenna. The peak-to-peak voltage swing, Vpp, at the antenna reaches 20 V and the peak current through the load, 200 mA. For a common-source (or common-emitter) stage to drive the load directly, the configurations shown in Figs. 12.1(a) and (b) require a supply voltage greater than Vpp. However, if the load is realized as an inductor [Fig. 12.1(c)], the drain ac voltage exceeds VDD, even reaching 2VDD (or higher). While allowing a lower supply voltage, the inductive load does not relax the “stress” on the transistor; the maximum drain-source voltage experienced by M1 is still at least 20 V (10 V above VDD = 10 V) if the stage must deliver 1 W to a 50-Ω load.

Figure 12.1. CS stages with (a) resistive, (b) current source, and (c) inductive load.



  

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