Justin Chow Jacob Huang Daniel Soledad ME 4447/6405 Student Lecture

 History  Properties  Types  BJT  JFET  MOSFET  Applications Overview Daniel Soledad

 Transistor History  “Transistor” is combination of “transconductance” and “variable resistor”  How Transistors Are Made ▪ Vacuum tubes ▪ Inefficient, fragile, bulky, generated a lot of heat ▪ First Transistors ▪ Semiconductors – Bell Labs 1947 Introduction

 Packaging  Surface Mount or Through Hole  Usually 3 or 4 terminal device ▪ Can be packaged into ICs  General Applications  Amplification/Regulation  Switches Introduction

 Current Controlled  i.e: BJT  The output current is proportional to input current  Voltage Controlled  i.e.: JFET, MOSFET  The output current is proportional to input voltage

 Bipolar Junction Transistor  3 semiconductor layers sandwiched together  Comes in two flavors NPN BJT PNP BJT BJT Transistor Justin Chow

 Diodes Forward BiasedReverse Biased current flowsno current flows when V PN >.6-.7V BJT Transistor

 BJT Basics (NPN)  BE Forward Biased  BC Reversed Biased  β=I B / I c ≈ 100  I E = I B + I C BJT Transistor emitter base collector Electron Flow

 Things to remember  PNP, biasing opposite  Conventional current vs electron flow  A small input current controls a much larger output current. BJT Transistor

 Operating Regions BJT Transistor Operating RegionParameters Cut Off V BE <0.7 V I B = I C = 0 Linear V BE >0.7 V I C = β*I B Saturated I B > 0, I C > 0 V BE >0.7 V, V CE 0.2 V

 Operating Regions BJT Transistor

 From 3 rd Exercise  Turns on/off coils digitally

 Common Emitter Amplifier BJT Transistor β=100

 Common Emitter Amplifier BJT Transistor I B = (V in − V B ) / 10000Ω = (V in − 0.7) / 10000Ω I C = β(V in − 0.7) / 10000Ω V out =10000*(V in -0.7)/1000 When V CE = 0.2V I C = 9.8 / 1000Ω = 9.8mA I B = I C / β = 0.098mA V in − 0.7 = (0.098mA)(10000Ω) V in = 1.68V or greater.

 Power Dissipation  P BJT = V CE * i CE  Should be below the rated transistor power  Important for heat dissipation as well BJT Transistor

Darlington Transistors  Increased Gain  β = β 1 * β 2  V BE = V BE1 + V BE2  Slower Switching  2N6282

FET Transistors  Analogous to BJT Transistors  Output is controlled by input voltage rather than by current  4 Pins vs. 3 BJTFET CollectorDrain BaseGate EmitterSource N/ABody

FET Transistors  FET (Field Effect Transistors)  MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor)  JFET (Junction Field-Effect Transistor)  MESFET  HEMT  MODFET  Most common are the n-channel MOSFET or JFET Jacob Huang

FET Transistors – Circuit Symbols  In practice the body and source leads are almost always connected  Most packages have these leads already connected B S G D B S G D S G D MOSFET JFET

MOSFET  Metal-Oxide Semiconductor F.E.T.  A.K.A. Insulated-Gate FET (IGFET)  2 Modes: Enhancement/Depletion

Depletion Mode  N-Channel  + V gs -> More electrons -> More Current  - V gs -> Less electrons -> Less current  P-Channel – Reversed  Different from BJT

Characteristic Curves for D-type Current flow B S G D

Enhancement Mode  N-Channel  V GS > V th -> Turns on device  V GS No Current  P-Channel  Reversed  Only E-type used now

Modes of Operation RegionCriteriaEffect on Current Cut-offV GS < V th I DS =0 LinearV GS > V th And V DS <V GS -V th Transistor acts like a variable resistor, controlled by V gs SaturationV GS > V th And V DS >V GS -V th Essentially constant current Current flow B S G D

Characteristic Curve for E-type Current flow B S G D

Power MOSFET  Used in high-power applications  Heat Sink  Vertical layout  Not Planar like other transistors

Junction gate FET  Reverse Bias V GS => Reduces channel size => Reduced Current  Defaults “on”

JFET as Switch  V gs = 0 “on”  |V gs |> |V p | “off” V p = Pinch-off or Cut-off Voltage

JFET Properties  Internal Capacitance  Bi-directional  Cut-off voltage is varying for each JFET  0.3V – 10V  N-Channel – Negative V GS  P-Channel – Positive V GS  Do not Forward Bias JFET – burn out

JFET Characteristic Curve

Comparison PropertyBJTMOSFETJFET GmBestWorstMedium SpeedHighMediumLow NoiseModerateWorstBest Good Switch NoYes High-Z GateNoYes ESD Sensitivity LessMoreLess

CMOS  Complementary MOS  Used in Logic Gates  P-channel (PMOS) to high  N-channel (NMOS) to low  HIGH usually +5 V  LOW usually ground  Q is high when A = 0, Q is low when A = 1

References Spring 2007/2008 Slides bjt.gif&imgrefurl= bridge/bjt_theory.html mon_Emitter_Amplifier_Circuit