Lecture15 - EEE 5320 Signal Paths Lecture XXX 12 15, p....

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EEE 5320 Lecture 12 Signal Paths The nodes, branches and transistor terminals that convey signals from the input of an amplifier to its output comprise the signal path of the amplifier. We’ve already been using this concept. We said that if the signal path enters a transistor’s base and leaves from its collector, that amplifier stage is common- emitter, and if it enters the emitter and leaves from the collector it’s common-base, and if the signal enters the base and leaves from the emitter, it’s an emitter follower, or common-collector. At this point it may be useful to say a bit more about the concept of a signal path. We know that in a voltage amplifier, a small change in an input voltage can produce a change in the output voltage. These small changes are represented as small-signal variations. The voltage gain of an amplifier stage is expressed as the ratio of the change in the output voltage divided by the corresponding change in the input voltage, or v out / v in = ! V out / ! V in . We also saw that we can create a composite (multi-stage) amplifier using a cascade connection, where the output of one stage connects to the input of the next. For a cascade configuration, we can multiply the voltage gains of the stages to get the gain of the overall circuit, as long as we include the input impedance of one stage as part of the load of the previous stage. In these examples, the input and output nodes and the gain stages that connect them define the circuit’s signal path. To allow for input or output current variables as well as voltages, we should include the input and output branches of each stage and their corresponding branch currents as parts of the signal path along with the nodes. If one of the branches has a non-negligible impedance in series with the signal path we should include an
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This note was uploaded on 01/17/2011 for the course EEL 5321 taught by Professor Dr.robertfox during the Fall '10 term at University of Florida.

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Lecture15 - EEE 5320 Signal Paths Lecture XXX 12 15, p....

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