Lecture 26 - BJT Introduction

Lecture 26 - BJT Introduction - Bipolar-Junction...

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1 EE360 – Lecture 26 Bipolar-Junction Transistors: Introduction Objective: To conceptually understand how BJTs function. Questions to be answered: • What is a BJT and how do we make one? • What are the modes of operation? • How do we describe the electrostatics of a BJT? • How does a BJT operate conceptually? EE360 – Lecture 26 Device Types pnp npn • Emitter usually heavily doped (i.e. N AE = 10 18 cm -3 ) • Base more lightly doped (i.e. N DB = 10 15 cm -3 ) • Collector even more lightly doped (i.e. N AC = 10 14 cm -3 ) • New notation: N AE = emitter acceptor concentration • Base is “narrow,” or else we would just have two pn junction diodes. From Pierret, pg. 372
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2 EE360 – Lecture 26 Circuit Symbols and Conventions • One way to remember the symbols: pnp = p ointing in p roudly npn = n ot p ointing in pnp npn From Pierret, pg. 372 EE360 – Lecture 26 Circuit Symbols and Conventions • Voltages and currents: – Subscripts indicate polarity (first subscript is positive) – Currents defined so that they are positive in the most common operating mode pnp npn From Pierret, pg. 372
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3 EE360 – Lecture 26 Currents and Voltages: Immediate Observations • Current into device = current out of device: I E = I C + I B • Total voltage drop around a loop must be zero: V EB + V BC + V CE = 0 • We only need to find two currents and two voltages to describe the device pnp BJT From Pierret, pg. 372 EE360 – Lecture 26
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Lecture 26 - BJT Introduction - Bipolar-Junction...

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