EE 330 Lect 21 Fall 2011

EE 330 Lect 21 Fall 2011 - EE 330 Lecture 21 Bipolar...

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EE 330 Lecture 21 Bipolar Devices Thyristors SCRs Triacs
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A-A’ Section B-B’ Section E C B vertical npn B C E E B C E C B lateral pnp C B E B C E Review from Last Lecture
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A-A’ Section B-B’ Section G D S S D G p-channel JFET Review from Last Lecture
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B E C E B C E C B lateral pnp E C B vertical npn B C E E C B Review from Last Lecture
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L G D S W Resistor Diode (capacitor) G D S S D G n-channel JFET Review from Last Lecture
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The vertical npn transistor Emitter area only geometric parameter that appears in basic device model Transistor much larger than emitter Base region very thin to provide large β Multiple-emitter devices often used (TTL Logic) and don’t significantly increase area The “flagship” device in most bipolar processes Review from Last Lecture
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Enhancement and Depletion MOS Devices • Enhancement Mode n-channel devices V T > 0 • Enhancement Mode p-channel devices V T < 0 • Depletion Mode n-channel devices V T < 0 • Depletion Mode p-channel devices V T > 0
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Enhancement and Depletion MOS Devices Depletion mode devices require only one additional mask step Older n-mos and p-mos processes usually had depletion device and enhancement device Depletion devices usually not available in CMOS because applications usually do not justify the small increasing costs in processing n-channel p-channel Enhancement Depletion
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The JFET In triode region under reverse bias (channel thins) S D G S D G
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The JFET In saturation (pinch-off) region under reverse bias and large V DS (channel pinches off) S D G S D G
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The JFET S D G GS P DSS DS D GS P DS GS P DS GS P 2 P 2 GS DSS GS P DS GS P P 0 V V 2I V I V -V - V V V V < V -V V2 V I 1- V V V < V -V V     D D S S G G n-channel p-channel p-channel JFET Square-law model of n-channel JFET Functionally identical to the square-law model of MOSFET Parameters I DSS and V P characterize the device I DSS proportional to W/L where W and L are width and length of n+ diff V P is negative for n-channel device, positive for p-channel device thus JFET is depletion mode device Must not forward bias GS junction by over about 300mV or excessive base current will flow Widely used as input stage for bipolar op amps
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The Schottky Diode C A Metal-Semiconductor Junction One contact is ohmic, other is rectifying Not available in all processes Relatively inexpensive adder in some processes Lower cut-in voltage than pn junction diode High speed
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The MESFET S G D
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EE 330 Lect 21 Fall 2011 - EE 330 Lecture 21 Bipolar...

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