CHAPTER 11Digital Upconversion and Downconversion

Previously, we discussed complex modulation and baseband signals. The whole point of this discussion is to create a signal that can be used to carry the information bits from one location to another, whether over copper wire, a fiber-optic cable, or electromagnetically through the air. In nearly all cases, the signal needs to ride on a carrier frequency to be efficiently sent from one location to another. To do this, the signal frequency spectrum needs to be able to be moved up and down the frequency axis at will. This is a process of (frequency) upconversion and downconversion. All early methods used analog circuits to accomplish this task. In the past couple of decades, digital circuits, particularly ...

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