Chapter 3DiodesFunctionality and PhysicalOperation2025/11/27
Chapter 3 Diodes Functionality and Physical Operation 1 2025/11/27
2Content3.1TheldealDiode3.2TerminalCharacteristicsofJunctionDiodes3.3ModelingtheDiodeForwardCharacteristic3.4OperationintheReverseBreakdownRegionZenerDiodes3.5RectifierCircuits（整流电路）3.6LimitingandClampingCircuits（限幅与钳位电路）3.7PhysicalOperationofDiodes3.8SpecialDiodeTypes3.9 TheSPiCEDiodeModel andSimulationExamples2025/11/27
Content 3.1 The Ideal Diode 3.2 Terminal Characteristics of Junction Diodes 3.3 Modeling the Diode Forward Characteristic 3.4 Operation in the Reverse Breakdown Region—Zener Diodes 3.5 Rectifier Circuits （整流电路） 3.6 Limiting and Clamping Circuits （限幅与钳位电路） 3.7 Physical Operation of Diodes 3.8 Special Diode Types 3.9 The SPICE Diode Model and Simulation Examples 2025/11/27 2
3.1Linear and Nonlinear DevicesSofar,almostallthedeviceswehavelearntare linearMany signal-processingfunctions,however,are implemented by nonlinear devicesP马鸟鸟马马万NonlinearamplifierLinearamplifier2025/11/27
2025/11/27 3 3.1 Linear and Nonlinear Devices ⚫ So far, almost all the devices we have learnt are linear ⚫ Many signal-processing functions, however, are implemented by nonlinear devices Linear amplifier Nonlinear amplifier
43.1 Symbol and characteristicDiode (二极管)is the simplest and most fundamentalnonlinear circuit elementAnodeCathode---Reverse bias.------Forwardbias--O(a) Diode circuit symbol(b) i-vcharacteristicofthe ideal diodeOO+Vi>0=v=0V<0=i=0(d) Equivalent circuit(c)Equivalentcircuitinthe forward directioninthereverse directionNote: measures should be taken to limit theforward current and the reversevoltage!2025/11/27
2025/11/27 4 (a) Diode circuit symbol + v - i Anode Cathode (b) i–v characteristic of the ideal diode -Reverse bias- -Forward bias- i 0 v (c) Equivalent circuit in the reverse direction v 0 v =0 + v - Note: measures should be taken to limit the forward current and the reverse voltage! ⚫ Diode (二极管) is the simplest and most fundamental nonlinear circuit element 3.1 Symbol and characteristic
53.2 Junction Diodes and its CharacteristicsThemost important region is(mA)theboundarybetweenn-typeand p-type semiconductor,which is called pn junction(pn结)Metal contactMetal contactpn junction(v)71n-typep-typeOOsiliconsiliconCathodeAnodeThediodei-vrelationship2025/11/27
(v) The diode i–v relationship (mA) 2025/11/27 5 pn junction ⚫ The most important region is the boundary between n-type and p-type semiconductor, which is called pn junction(pn结) 3.2 Junction Diodes and its Characteristics
63.2 Junction Diodes and its Characteristicsi(mA)Thediode i-vrelationship(Notethescaleexpansion)compression)ForwardCompressedVzKscale0.7VOU0.5Vcut-in voltageeooeReverseBreakdown+UNC(nA)2025/11/27
2025/11/27 6 (mA) (nA) The diode i–v relationship (Note the scale expansion / compression) cut-in voltage 3.2 Junction Diodes and its Characteristics
3.3The Diode ModelsMathematic Model :nVr -1)/=nVForwardbiasedReverse biasedwhereI.saturationcurrentkTthermal voltage(~25 mv at room temperature)VT :qn = 1~2 (In general, n = 1)2025/11/27
2025/11/27 7 ⚫ Mathematic Model： − = − s n V v s n V v s I I e i I e T T ( 1) Forward biased Reverse biased 3.3 The Diode Models where 𝑰𝒔 saturation current 𝒗𝑻 = 𝒌𝑻 𝒒 thermal voltage(~25 mv at room temperature) 𝒏 = 𝟏𝟐 (In general, n = 1)
83.3TemperaturedependenceTT22mVPT>TVoltagedrop@-2mV/oCTemperaturedependenceofthediodeforwardcharacteristic2025/11/27
2025/11/27 8 Temperature dependence of the diode forward characteristic Voltage drop @-2 mV/C 3.3 Temperature dependence
93.3The Diode ModelsCircuit Model : usually derived byapproximating the curve into piecewise-lineAccording to practical applications,there aredifferentmodels,suchas>Simplifieddiode model>Theconstant-voltage-dropmodelSmall-signalmodel>High-frequency modelZenerDiode Model2025/11/27
2025/11/27 9 ⚫ Circuit Model : usually derived by approximating the curve into piecewise-line ⚫ According to practical applications, there are different models, such as ➢ Simplified diode model ➢ The constant-voltage-drop model ➢ Small-signal model ➢ High-frequency model ➢ Zener Diode Model 3.3 The Diode Models
103.3ldeal Diode Model·Forwardbiasshortcircuit·Reversebias→opencircuit-ReversebiasForwardbias02025/11/27
2025/11/27 10 3.3 Ideal Diode Model ⚫ Forward bias → short circuit ⚫ Reverse bias → open circuit