Berkeley ELENG 105 - Lecture 21: BJTs (Bipolar Junction Transistors) (19 pages)

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Lecture 21: BJTs (Bipolar Junction Transistors)



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Lecture 21: BJTs (Bipolar Junction Transistors)

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Pages:
19
School:
University of California, Berkeley
Course:
Eleng 105 - Microelectronic Devices and Circuits
Microelectronic Devices and Circuits Documents

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EECS 105 Spring 2004 Lecture 22 Lecture 21 BJTs Bipolar Junction Transistors Prof J S Smith Department of EECS University of California Berkeley EECS 105 Spring 2004 Lecture 22 Prof J S Smith Context In Friday s lecture we discussed BJTs Bipolar Junction Transistors Today we will find large signal models for the bipolar junction transistor and start exploring how to use transistors to make amplifiers and other analog devices Department of EECS University of California Berkeley 1 EECS 105 Spring 2004 Lecture 22 Prof J S Smith Reading Today s lecture will finish chapter 7 Bipolar Junction Transistors BJT s Then we will start looking at amplifiers chapter 8 in the text Department of EECS University of California Berkeley EECS 105 Spring 2004 Lecture 22 Prof J S Smith Lecture Outline z z z z BJT Physics 7 2 BJT Ebers Moll Equations 7 3 BJT Large Signal Models BJT Small Signal Models Next Circuits Department of EECS University of California Berkeley 2 EECS 105 Spring 2004 Lecture 22 Prof J S Smith Currents in the BJT z z A BJT is ordinarily designed so that the minority carrier injection into the base is far larger than the minority carrier injection into the emitter It is also ordinarily designed such that almost all the minority carriers injected into the base make it all the way across to the collector Department of EECS University of California Berkeley EECS 105 Spring 2004 Lecture 22 Prof J S Smith Current controlled z So the current is determined by the minority current across the emitter base junction IC I S e z qVBE kT But since the majority of the minority current goes right through the base to the collector IC I E z And so the amount of current that must be supplied by the base is small compared to the current controlled I C I B Department of EECS University of California Berkeley 3 EECS 105 Spring 2004 Lecture 22 Prof J S Smith BJT operating modes z Forward active z Saturation z Emitter Base forward biased Base Collector reverse biased Both junctions are



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