拉扎维授课课件-Ch1-8.ppt

Click to edit Master text styles,CH1 Why Microelectronics?,*,Click to edit Master title style,Click to edit Master text styles,CH1 Why Microelectronics?,*,Click to edit Master title style,Click to edit Master text styles,CH1 Why Microelectronics?,*,Click to edit Master title style,Click to edit Master title style,Click to edit Master text styles,CH1 Why Microelectronics?,*,CH1 Why Microelectronics?,*,Click to edit Master title style,Click to edit Master text styles,CH1 Why Microelectronics?,*,Click to edit Master title style,Click to edit Master title style,Click to edit Master text styles,*,Click to edit Master title style,Click to edit Master text styles,*,Fundamentals of Microelectronics,CH1 Why Microelectronics?,CH2 Basic Physics of Semiconductors,CH3 Diode Circuits,CH4 Physics of Bipolar Transistors,CH5 Bipolar Amplifiers,CH6 Physics of MOS Transistors,CH7 CMOS Amplifiers,CH8 Operational Amplifier As A Black Box,1,1.1 Electronics versus Microelectronics,1.2 Example of Electronic System:Cellular Telephone,1.3 Analog versus Digital,Chapter 1 Why Microelectronics?,2,Cellular Technology,An important example of microelectronics.,Microelectronics exist in black boxes that process the received and transmitted voice signals.,3,CH1 Why Microelectronics?,Frequency Up-conversion,Voice is“up-converted”by multiplying two sinusoids.,When multiplying two sinusoids in time domain,their spectra are convolved in frequency domain.,4,CH1 Why Microelectronics?,Transmitter,Two frequencies are multiplied and radiated by an antenna in(a).,A power amplifier is added in(b)to boost the signal.,5,CH1 Why Microelectronics?,Receiver,High frequency is translated to DC by multiplying by f,C,.,A low-noise amplifier is needed for signal boosting without excessive noise.,6,CH1 Why Microelectronics?,Digital or Analog?,X,1,(t),is operating at 100Mb/s and,X,2,(t),is operating at 1Gb/s.,A digital signal operating at very high frequency is very“analog”.,7,CH1 Why Microelectronics?,Chapter 2 Basic Physics of Semiconductors,2.1 Semiconductor materials and their properties,2.2 PN-junction diodes,2.3 Reverse Breakdown,8,Periodic Table,This abridged table contains elements with three to five valence electrons,with Si being the most important.,11,CH2 Basic Physics of Semiconductors,Silicon,Si has four valence electrons.Therefore,it can form covalent bonds with four of its neighbors.,When temperature goes up,electrons in the covalent bond can become free.,12,CH2 Basic Physics of Semiconductors,Electron-Hole Pair Interaction,With free electrons breaking off covalent bonds,holes are generated.,Holes can be filled by absorbing other free electrons,so effectively there is a flow of charge carriers13,CH2 Basic Physics of Semiconductors,Free Electron Density at a Given Temperature,E,g,or bandgap energy determines how much effort is needed to break off an electron from its covalent bond.,There exists an exponential relationship between the free-electron density and bandgap energy.,14,CH2 Basic Physics of Semiconductors,Doping(N type),Pure Si can be doped with other elements to change its electrical properties.,For example,if Si is doped with P(phosphorous),then it has more electrons,or becomes type N(electron).,15,CH2 Basic Physics of Semiconductors,Doping(P type),If Si is doped with B(boron),then it has more holes,or becomes type P.,16,CH2 Basic Physics of Semiconductors,Summary of Charge Carriers,17,CH2 Basic Physics of Semiconductors,Electron and Hole Densities,The product of electron and hole densities is ALWAYS equal to the square of intrinsic electron density regardless of doping levels.,Majority Carriers:,Minority Carriers:,Majority Carriers:,Minority Carriers:,18,CH2 Basic Physics of Semiconductors,First Charge Transportation Mechanism:Drift,The process in which charge particles move because of an electric field is called drift.,Charge particles will move at a velocity that is proportional to the electric field.,19,CH2 Basic Physics of Semiconductors,Current Flow:General Case,Electric current is calculated as the amount of charge in,v,meters that passes thru a cross-section if the charge travel with a velocity of,v,m/s.,20,CH2 Basic Physics of Semiconductors,Current Flow:Drift,Since velocity is equal to,E,drift characteristic is obtained by substituting V with,E,in the general current equation.,The total current density consists of both electrons and holes.,21,CH2 Basic Physics of Semiconductors,Velocity Saturation,A topic treated in more advanced courses is velocity saturation.,In reality,velocity does not increase linearly with electric field.It will eventually saturate to a critical value.,22,CH2 Basic Physics of Semiconductors,Second Charge Transportation Mechanism:Diffusion,Charge particles move from a region of high concentration to a region of low concentration.It is analogous to an every day example of an ink droplet in water.,23,CH2 Basic Physics of Semiconductors,Current Flow:Diffusion,Diffusion current is proportional to the gradient of charge(dn/dx)along the direction of current flow.,Its total current density consists of both electrons and holes.,24,CH2 Basic Physics of Semiconductors,Example:Linear vs.Nonlinear Charge Density Profile,Linear charge density profile means constant diffusion current,whereas nonlinear charge density profile means varying diffusion current.,25,CH2 Basic Physics of Semiconductors,Einsteins Relation,While the underlying physics behind drift and diffusion currents are totally different,Einsteins relation provides a mysterious link between the two.,26,CH2 Basic Physics of Semiconductors,PN Junction(Diode),When N-type and P-type dopants are introduced side-by-side in a semiconductor,a PN junction or a diode is formed.,27,CH2 Basic Physics of Semiconductors,Diodes Three Operation Regions,In order to understand the operation of a diode,it is necessary to study its three operation regions:equilibrium,reverse bias,and forward bias.,28,CH2 Basic Physics of Semiconductors,Current Flow Across Junction:Diffusion,Because each side of the junction contains an excess of holes or electrons compared to the other side,there exists a large concentration gradient.Therefore,a diffusion current flows across the junction from each side.,29,CH2 Basic Physics of Semiconductors,Depletion Region,As free electrons and holes diffuse across the junction,a region of fixed ions is left behind.This region is known as the“depletion region.”,30,CH2 Basic Physics of Semiconductors,Current Flow Across Junction:Drift,The fixed ions in depletion region create an electric field that results in a drift current.,31CH2 Basic Physics of Semiconductors,Current Flow Across Junction:Equilibrium,At equilibrium,the drift current flowing in one direction cancels out the diffusion current flowing in the opposite direction,creating a net current of zero.,The figure shows the charge profile of the PN junction.,32,CH2 Basic Physics of Semiconductors,Built-in Potential,Because of the electric field across the junction,there exists a built-in potential.Its derivation is shown above.,33,CH2 Basic Physics of Semiconductors,Diode in Reverse Bias,When the N-type region of a diode is connected to a higher potential than the P-type region,the diode is under reverse bias,which results in wider depletion region and larger built-in electric field across the junction.,34,CH2 Basic Physics of Semiconductors,Reverse Biased Diodes Application:Voltage-Dependent Capacitor,The PN junction can be viewed as a capacitor.By varying V,R,the depletion width changes,changing its capacitance value;therefore,the PN junction is actually a voltage-dependent capacitor.,35,CH2 Basic Physics of Semiconductors,Voltage-Dependent Capacitance,The equations that describe the voltage-dependent capacitance are shown above.,36,CH2 Basic Physics of Semiconductors,Voltage-Controlled Oscillator,A very important application of a reverse-biased PN junction is VCO,in which an LC tank is used in an oscillator.By changing V,R,we can change C,which also changes the oscillation frequency.,37,CH2 Basic Physics of Semiconductors,Diode in Forward Bias,When the N-type region of a diode is at a lower potential than the P-type region,the diode is in forward bias.,The depletion width is shortened and the built-in electric field decreased.,38,CH2 Basic Physics of Semiconductors,Minority Carrier Profile in Forward Bias,Under forward bias,minority carriers in each region increase due to the lowering of built-in field/potential.Therefore,diffusion currents increase to supply these minority carriers.,39,CH2 Basic Physics of Semiconductors,Diffusion Current in Forward Bias,Diffusion current will increase in order to supply the increase in minority carriers.The mathematics are shown above.,40,CH2 Basic Physics of Semiconductors,Minority Charge Gradient,Minority charge profile should not be constant along the x-axis;otherwise,there is no concentration gradient and no diffusion current.,Recombination of the minority carriers with the majority carriers accounts for the dropping of minority carriers as they go deep into the P or N region.,41,CH2 Basic Physics of Semiconductors,Forward Bias Condition:Summary,In forward bias,there are large diffusion currents of minority carriers through the junction.However,as we go deep into the P and N regions,recombination currents from the majority carriers dominate.These two currents add up to a constant value.,42,CH2 Basic Physics of Semiconductors,IV Characteristic of PN Junction,The current and voltage relationship of a PN junction is exponential in forward bias region,and relatively constant in reverse bias region.,43,CH2 Basic Physics of Semiconductors,Parallel PN Junctions,Since junction currents are proportional to the junctions cross-section area.Two PN junctions put in parallel are effectively one PN junction with twice the cross-section area,and hence twice the current.,44,CH2 Basic Physics of Semiconductors,Constant-Voltage Diode Model,Diode operates as an open circuit if V,D,0,V,BC,I,B,)and,V,BE,variations.,183,CH5 Bipolar Amplifiers,Design Procedure,Choose an I,C,to provide the necessary small signal parameters,g,m,r,etc.,Considering the variations of R,1,R,2,and V,BE,choose a value for V,RE.,With V,RE,chosen,and V,BE,calculated,V,x,can be determined.,Select R,1,and R,2,to provide V,x.,184,Self-Biasing Technique,This bias technique utilizes the collector voltage to provide the necessary V,x,and I,B,.,One important characteristic of this technique is that collector has a higher potential than the base,thus guaranteeing active operation of the transistor.,185,CH5 Bipolar Amplifiers,Self-Biasing Design Guidelines,(1)provides,insensitivity to .,(2)provides insensitivity to variation in V,BE.,186,CH5 Bipolar Amplifiers,Summary of Biasing Techniques,187,CH5 Bipolar Amplifiers,PNP Biasing Techniques,Same principles that apply to NPN biasing also apply to PNP biasing with only polarity modifications.,188,CH5 Bipolar Amplifiers,Possible Bipolar Amplifier Topologies,Three possible ways to apply an input to an amplifier and three possible ways to sense its output.,However,in reality only three of six input/output combinations are useful.,189,CH5 Bipolar Amplifiers,Study of Common-Emitter Topology,Analysis of CE Core,Inclusion of Early Effect,Emitter Degeneration,Inclusion of Early Effect,CE Stage with Biasing,190,Common-Emitter Topology,191,CH5 Bipolar Amplifiers,Small Signal of CE Amplifier,192,CH5 Bipolar Amplifiers,Limitation on CE Voltage Gain,Since g,m,can be written as I,C,/V,T,the CE voltage gain can be written as the ratio of V,RC,and V,T.,V,RC,is the potential difference between V,CC,and V,CE,and V,CE,cannot go below V,BE,in order for the transistor to be in active region.,193,CH5 Bipolar Amplifiers,Tradeoff between Voltage Gain and Headroom,194,CH5 Bipolar Amplifiers,I/O Impedances of CE Stage,When measuring output impedance,the input port has to be grounded so that V,in,=0.,195,CH5 Bipolar Amplifiers,CE Stage Trade-offs,196,CH5 Bipolar Amplifiers,Inclusion of Early Effect,Early effect will lower the gain of the CE amplifier,as it appears in parallel with R,C,.,197,CH5 Bipolar Amplifiers,Intrinsic Gain,As R,C,goes to infinity,the voltage gain reaches the product of g,m,and r,O,which represents the maximum voltage gain the amplifier can have.,The intrinsic gain is independent of the bias current.,198,CH5 Bipolar Amplifiers,Current Gain,Another parameter of the amplifier is the current gain,which is defined as the ratio of current delivered to the load to the current flowing into the input.,For a CE stage,it is equal to,.,199,CH5 Bipolar Amplifiers,Emitter Degeneration,By inserting a resistor in series with the emitter,we“degenerate”the CE stage.,This topology will decrease the gain of the amplifier but improve other aspects,such as linearity,and input impedance.,200,CH5 Bipolar Amplifiers,Small-Signal Model,Interestinglythis gain is equal to the total load resistance to ground divided by 1/g,m,plus the total resistance placed in series with the emitter.,201,CH5 Bipolar Amplifiers,Emitter Degeneration Example I,The input impedance of Q,2,can be combined in parallel with R,E,to yield an equivalent impedance that degenerates Q,1,.,202,CH5 Bipolar Amplifiers,Emitter Degeneration Example II,In this example,the input impedance of Q,2,can be combined in parallel with R,C,to yield an equivalent collector impedance to ground.,203,CH5 Bipolar Amplifiers,Input Impedance of Degenerated CE Stage,With emitter degenerationthe input impedance is increased from r,to,r,+(+1)R,E,;a desirable effect.,204,CH5 Bipolar Amplifiers,Output Impedance of Degenerated CE Stage,Emitter degeneration does not alter the output impedance in this case.(More on this later.),205,CH5 Bipolar Amplifiers,Capacitor at Emitter,At DC the capacitor is open and the current source biases the amplifier.,For ac signals,the capacitor is short and the amplifier is degenerated by R,E,.,206,CH5 Bipolar Amplifiers,Example:Design CE Stage with Degeneration as a Black Box,If g,m,R,E,is much greater than unity,G,m,is more linear.,207,CH5 Bipolar Amplifiers,Degenerated CE Stage with Base Resistance,208,CH5 Bipolar Amplifiers,Input/Output Impedances,R,in1,is more important in practice as R,B,is often the output impedance of the previous stage.,209,CH5 Bipolar Amplifiers,Emitter Degeneration Example III,210,CH5 Bipolar Amplifiers,Output Impedance of Degenerated Stage with V,A,1/g,m,.,R,1,and R,2,are chosen so that V,b,is at the appropriate value and the current that flows thru the divider is much larger than the base current.,Capacitors are chosen to be small compared to 1/g,m,at the required frequency.,248,CH5 Bipolar Amplifiers,Emitter Follower(Common Collector Amplifier),249,CH5 Bipolar Amplifiers,Emitter Follower Core,When the input is increased by,V,output is also increased by an amount that is less than V due to the increase in collector current and hence the increase in potential drop across R,E,.,However the absolute values of i