Review Outline. 1. Chapter 1: Signals and Amplifiers. 2. Chapter 3: Semiconductors. 3. Chapter 4: Diodes. EE 3110 Microelectronics I

Transcription

1 Review Outline 1 1. Chater 1: Signals and Amlifiers 2. Chater 3: Semiconductors 3. Chater 4: Diodes

2 1.1 Signals Signal contains information e.g. voice of radio announcer reading the news 2 Transducer device which converts signal from non-electrical to electrical form e.g. microhone (sound to electrical) Process an oeration which allows an observer to understand this information from a signal generally done electrically

3 1.4 Amlifiers 3 Q: Why is signal amlification needed? A: Because many transducers yield outut at low ower levels (mw or nw) Linearity is roerty of an amlifier which ensures a signal is not altered from amlification Distortion is any unintended change in outut

4 1.5.1 Voltage Amlifiers 4 model of amlifier inut terminals Ri inut voltag e vi ( vs) R R source volt. i s source and inut resistances model of amlifier outut terminals RL outut vo l tage v o ( A v vo i) R R oen-ckt outut voltage L o outut and load resistances Figure 1.16 (b): voltage amlifier with inut signal source

5 1.5.1 Voltage Amlifiers 5 Ideal amlifier model is function of v s and A vo only!! It is assumed that R o << R L It is assumed that R i >> R s R R v A v A v i L o vo s vo s Ri Rs RL Ro ideal model non-ideal model Key characteristics of ideal voltage amlifier model 1) Source resistance R S and load resistance R L have no effect on gain 2) High inut resistance R i (>>R S ) and low outut resistance R o (<<R L )

6 Examle 1.3: Cascaded Amlifier Configurations 6 High Inut Resistance Modest Gain Low Inut Resistance High Gain Low Outut Resistance Unity Gain Figure 1.17: Three-stage amlifier for Examle 1.3.

7 Review Outline 7 1. Chater 1: Signals and Amlifiers 2. Chater 3: Semiconductors 3. Chater 4: Diodes

8 3.1. Intrinsic Semiconductors Valence electron is an electron that articiates in the formation of chemical bonds. Lies in the outermost electron shell of an element The number of valence electrons that an atom has determines the kinds of chemical bonds that it can form. Covalent bond is a form of chemical bond in which two atoms share a air of electrons By sharing their outer most (valence) electrons, atoms can fill u their outer electron shell and gain stability valence electron 8 covalent bond

9 -tye semiconductor doed with trivalent imurity atom (e.g. Boron) 3.2 Doed Semiconductors n-tye semiconductor doed with entavalent imurity atom (e.g. Phoshorus) 9

10 3.3 Current Flow in Semiconductors 10 Summary Holes (absence of electrons, ) and free electrons (n): -tye semiconductor: holes are majority carriers ( ), free electrons (n ) are minority carriers n-tye semiconductor: free electrons are majority carriers (n n ), holes are minority carriers ( n ) Two distinct mechanisms for current flow (movement of charge carriers) Drift Current (I S ) Diffusion Current (I D )

11 Mobility 11 Holes have less mobility than free electrons Why? Free electrons are loosely tied to the nucleus and are closer to the conduction band (higher orbits, see slide 19) Holes are absence of electrons in the covalent bond between Si atoms and B Holes are locked or subjected to the stronger atomic force ulled by the nucleus than the electrons residing in the higher shells or farther shells So, holes have a lower mobility

12 3.4.1 Physical Structure 12 n junction (diode) structure -tye semiconductor n-tye semiconductor metal contact for connection

13 n junction: modes of oeration 13 (a) Oen-circuit:voltage dro across deletion region = V 0, I D = I S (b) Reverse bias:voltage dro across deletion region = V 0 +V R, I D < I S (c) Forward bias:voltage dro across deletion region = V 0 -V F, I D > I S

14 Reverse-Bias Case 14 Observe that increased barrier voltage will be accomanied by (1) Increase in stored uncovered charge on both sides of junction (2) wider deletion region (eq3.31) W width of deletion regionp S electrical ermiability of silicon ( E12 F / cm) P q magnitude of electron chargep N A concentration of accetor atomsp ND concentration of donor atomsp V 0 barrier / junction built-in voltagep V externally alied reverse-bias voltagep R W x x ( V V ) S n 0 R q NA ND action: relace V with V V NN A D (eq3.32) QJ A 2 Sq ( V0 VR) NA ND action: 0 relace V with V V 0 R 0 0 R Q magnitude of charge stored on either side of deletion regionp J

15 Forward-Bias Case 15 Observe that decreased barrier voltage will be accomanied by (1) Decrease in stored uncovered charge on both sides of junction (2) Smaller deletion region W width of deletion regionp S electrical ermiability of silicon ( E12 F / cm) P q magnitude of electron chargep NA concentration of accetor atomsp ND concentration of donor atomsp V barrier / junction built-in voltagep V externally alied forward-bias voltagep F W x x ( V V ) S n 0 F q NA ND action: relace V with V V 0 NN Q A 2 q ( V V A D J S 0 F NA ND action: relace V0 with V0 V F ) 0 0 F Q magnitude of charge stored on either side of deletion regionp J

16 Review Outline Chater 1: Signals and Amlifiers 2. Chater 3: Semiconductors 3. Chater 4: Diodes

17 4.1 The Ideal Diode 17 tye n tye Off On Off (Reverse Biased) Oen Circuit On (Forward Biased) Short Circuit Ideal diode most fundament nonlinear circuit element Oerates in two modes: Off (reverse biased, (c)), On (forward biased, (d))

18 4.3.5 Constant Voltage-Dro Model The constant voltagedro diode model assumes that the sloe of I D vs. V D is 0.7V 18 Negligible difference between values obtained from the exonential model (most accurate) Examle

19 4.3.1 Exonential Model: I D I S e V D / V T 19 Q: How does one solve for I D in circuit to right? A: Grahical method Iterative method eq 4.6 eq 4.7 I I D D V I S DD e V R V D / V T D

20 Terminal Characteristics of Junction Diodes 20 I-V curve consists of three characteristic regions forward bias: v > 0 reverse bias: v < 0 breakdown: v << 0

21 Exercise Find I and V using 4.4 (a) Ideal diode model (b) Constant voltage dro model Ans: 4.4 (a) 2 ma, 0V (c) 0 ma, -5V

22 22 Figure P4.3 Microelectronic Circuits, Sixth Edition Sedra/Smith Coyright 2010 by Oxford University Press, Inc.

23 Examles and Excercises 23 Examle 1: V DD = 5 V R = 1 kω I D = V Excercises D4.11, 4.12 (a) Model Tye/ Parameter Ideal diode model Constant voltage-dro model V D 0 V 0.7 V I D 5 ma 4.3mA Exonential Model: Iterative Method V (2nd iteration) ma (2nd iteration)

24 4.3.1 Exonential Model: I D I S e V D / V T 24 Q: How does one solve for I D in circuit to right? A: Grahical method Iterative method eq 4.6 eq 4.7 I I D D V I S DD e V R V D / V T D

25 4.3.7 Small Signal Model DC analysis: Use constant voltage dro model AC analysis: Use resistor as diode Notation: DC only uer-case w/ uer-case subscrit, V D Time-varying only lower-case w/ lower-case subscrit, v d total instantaneous lower-case w/ uer-case subscrit, v D 25 AC (time varying) DC

26 4.3.7 Small Signal Model 26 Substitute eq.4.9 in eq.4.10 Slit this exonential Redefine total instant current in terms of DC comonent (I D ) and time-varying voltage (v d ) Aly ower series exansion to (4.12) and kee uto first order terms i I v D D ( t) D I I D 1 s e V D ( t) V / V D T v v V d d T d ( t) (eq4.14 ) (eq4.8) (eq4.9)

27 4.3.7 Small Signal Model 27 (eq4.14 ) Small signal aroximation total instant current (i D ) small-signal current (i d. ) small-signal resistance (r d. ) accurate for v d < 5mV amlitude (not eak to eak) somewhat accurate for v d > 5mV I D i () t I v VT D D d i () t I i i r D D d d d 1 r d V I T D v d i d

28 Examle V + = 10 V with 1 V eak am at 60 Hz (ower suly rile) R = 10 kω I D = V Calculate dc voltage and the amlitude of ac signal across the diode.

29 4.4 Zener Diodes 29 V Z V ZO r Z I Z V ZK V ZO We will revisit Zener diode in section 4.6 (limiter circuit)

30 On Alication: Rectifier On Off On Off Rectifier converts ac signal in to dc signal 30 During ositive cycle, current will flow through the diode (forward biased) During negative cycle, no current will flow through the diode (reverse biased)

31 Half Wave Rectifier with a Filter Caacitor 31

32 Full-Wave Rectifier 32 Center-taing of the transformer, allowing reversal of certain currents

33 Bridge Rectifier 33