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Unformatted text preview: Transistor Basics Lab 1: The Bipolar (Junction) Transistor ECE 327: Electronic Devices and Circuits Laboratory I Abstract In the lab, we explore several common transistor circuits; we build a common-emitter amplifier, a pnp current source, an npn emitter follower, and class B and class AB (i.e., biased) pushpull amplifiers. Here, we introduce basic operating guidelines for bipolar transistors and outlines of these circuits. Contents 1 Bipolar Junction Transistor Model 2 2 The Ideal Bipolar Junction Transistor 3 Saturation Mode and Compliance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3 Common-Emitter Amplifier 4 4 pnp Current Sources 5 5 pnp Current Mirror 6 6 npn Emitter Follower 7 7 Simple Class-B PushPull Amplifier 8 8 Biased Class-B PushPull Amplifier 9 A Bootstrapping for Higher Input Impedance 10 B Parts 11 Note about diode/bandgap conventions: We use the convention that a typical silicon BJT base emitter diode drop is 0 . 65 V and a standard general purpose silicon diode drop is 0 . 6 V. Other conventions use 0 . 6 V or 0 . 7 V for one or both. Measured laboratory results will most likely be between these two values. Diodes and BJTs implemented on the same integrated circuit (i.e., on the same piece of silicon) may have equivalent characteristics. That is, the diodes and transistors can be matched . Matched components are convenient to use in many circuit designs. We use discrete elements in this laboratory, and so it is not possible to match components unless theyre all implemented within the one part. In the laboratory, a diode-connected transistor (i.e., shorted base and collector) may match the baseemitter characteristics of another transistor better than a diode. Diode drops are strongly temperature dependent. Room-temperature transistors have baseemitter drops around 0 . 65 V, but hot transistors have drops near 0 . 5 V because they need less excitation for conduction. So temperature matching is just as important as component matching. Internal temperature compensation in bandgap voltage references lets them provide a temperature-independent voltage reference. Their output reference of 1 . 22 V is the Silicon diode drop at absolute zero (i.e., 0 K or 273 . 15 C). It is not a coincidence that the Silicon bandgap (i.e., the energy separating valence and conduction electron bands) is 1 . 22 eV. Temperature dependence and manufacturing variations (and the Early effect) are always a concern. Copyright c circlecopyrt 20072009 by Theodore P. Pavlic Creative Commons Attribution-Noncommercial 3.0 License Page 1 of 11 ECE 327 [Lab 1: The Bipolar (Junction) Transistor] Transistor Basics 1 Bipolar Junction Transistor Model A bipolar junction transistor (BJT) can be in three modes: cutoff mode : Transistor acts like an open switch between collector and emitter (i.e., collectoremitter resistance is infinite)....
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