Transistor Action 3c6q4z

Dr. Mohammed Gulam Ahamad

Transistors

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Objectives  Describe the basic properties of a bipolar junction transistor (BJT), including the names of the terminals and the classifications as NPN or PNP.  Construct equivalent circuits of the BJT for both cutoff and saturation.  Describe the nature of both the base and collector characteristic curves for a BJT.

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Objectives  Describe the three regions of operation for a BJT.  Define dc current gain for a BJT and discuss its significance.  Design a BJT switch using worst-case conditions.  Discuss the family tree for the field effect transistor (FET) and show the various classifications.

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Objectives  Describe the general properties of the junction field effect transistor (JFET).  Describe the three regions of operation for a JFET.  Describe the general properties of the metaloxide semiconductor field effect transistor (MOSFET).  Explain the differences between the depletionmode MOSFET and enhancement-mode MOSFET. 4

Objectives  Discuss how FETs can be used as switches.  Provide a qualitative explanation of how BJTs and FETs can function as amplifiers.  Provide a general comparison between BJTs and FETs.

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7-1 Introduction  Why Study Transistors?

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7-2 Bipolar Junction Transistor  NPN and PNP  NPN Layout  PNP Layout  Analogy to Two Diodes  Basic Operation  Relationship for Currents

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Layout of an NPN transistor and its schematic symbol.

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Layout of a PNP transistor and its schematic symbol.

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Models to assist in visualizing BJT as two diodes.

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7-3 BJT Operating Regions  Cutoff Region  Saturation Region  Active Region

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Ideal model of BJT in cutoff region.

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Ideal model of BJT in saturation region.

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Better models for BJTs in saturation region.

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7-4 BJT Characteristic Curves  Common-Emitter Form  Measurement Circuit  Base Characteristics  Collector Characteristics  Operating Regions  DC Current Gain  Polarities and Current Directions  Variations in the Current Gain 15

Circuit that can be used to measure transistor characteristics.

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Base characteristic with collector-toemitter voltage constant.

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Collector characteristics of an ideal representative BJT.

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Three regions of operation for a BJT.

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Reference positive directions for both NPN and PNP transistors.

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7-5 Brief Look at a Classical BJT Amplifier Circuit

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Classical BJT amplifier circuit that operates in active region.

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7-6 BJT Switches  Saturation and Cutoff in Switches  NPN Switch  PNP Switch  Increase of Base Current After Saturation

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BJT switch using an NPN transistor.

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BJT switch using a PNP transistor.

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7-7 Field Effect Transistor Family  Family Tree  JFETs  MOSFETs

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Classification scheme for field effect transistors.

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7-8 Junction Field Effect Transistors  N-Channel Layout  Three JFET Operating Regions  Obtaining JFET Characteristics  Gate-to-Source Cutoff Voltage and the Cutoff Region  Drain Characteristics  Ohmic Region  Beyond Pinchoff Region  Formula for JFET Drain Current 28

Construction of an N-channel JFET and the schematic symbol.

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Circuit that can be used to measure Nchannel JFET characteristics.

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Ideal model of the JFET in the cutoff region.

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Idealized drain characteristics of Nchannel JFET in linear portion of the ohmic region.

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Drain characteristics for an ideal representative N-channel JFET.

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7-9 Brief Look at Classical JFET Amplifier Circuits

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Classical JFET amplifier circuit that operates in beyond pinchoff region.

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7-10 MOSFETs  Depletion-Mode MOSFET  Enhancement-Mode MOSFET  Threshold Voltage  Drain Current Equation

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Construction of an N-channel depletion-mode MOSFET with external connection for substrate and the schematic symbol.

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Construction of an N-channel enhancementmode MOSFET with external connection for substrate and the schematic symbol.

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Drain characteristics for an ideal representative N-channel enhancement-mode MOSFET.

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7-11 FET Switches  JFET Resistance in Ohmic Region  N-Channel JFET Switch  N-Channel MOSFET Switch  Analog Multiplexer

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N-channel JFET switch.

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Switch using an N-channel enhancementmode MOSFET.

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Implementation of a four-channel multiplexer using P-channel JFET switches and an operational amplifier.

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7-12 FET Schematic Summary

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Schematic diagrams for different types of field effect transistors.

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