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Chapter 5 Bipolar Junction Transistors

Chapter 5 Bipolar Junction Transistors. Microelectronic Circuit Design Richard C. Jaeger Travis N. Blalock. Circuit Representations for the Transport Models.

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Chapter 5 Bipolar Junction Transistors

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  1. Chapter 5Bipolar Junction Transistors Microelectronic Circuit Design Richard C. Jaeger Travis N. Blalock Microelectronic Circuit Design McGraw-Hill

  2. Circuit Representations for the Transport Models In npn transistor (expressions analogous for pnp transistors), total current traversing base is modeled by a current source given by: Diode currents correspond directly to the two components of base current. Microelectronic Circuit Design McGraw-Hill

  3. Operation Regions of Bipolar Transistors Binary Logic States Microelectronic Circuit Design McGraw-Hill

  4. i-v Characteristics of Bipolar Transistor: Common-Emitter Output Characteristics For iB = 0, transistor is cutoff. If iB > 0, iC also increases. For vCE > vBE, npn transistor is in forward-active region, iC = bFiB is independent of vCE. For vCE < vBE, transistor is in saturation. For vCE < 0, roles of collector and emitter reverse. Microelectronic Circuit Design McGraw-Hill

  5. i-v Characteristics of Bipolar Transistor: Common-Emitter Transfer Characteristic Defines relation between collector current and base-emitter voltage of transistor. Almost identical to transfer characteristic of pn junction diode Setting vBC = 0 in the collector-current expression yields Collector current expression has the same form as that of the diode equation Microelectronic Circuit Design McGraw-Hill

  6. Simplified Forward-Active Region Model In forward-active region, emitter-base junction is forward-biased and collector-base junction is reverse-biased. vBE > 0, vBC < 0 If we assume that then the transport model terminal current equations simplify to BJT is often considered a current-controlled device, though fundamental forward-active behavior suggests a voltage- controlled current source. Microelectronic Circuit Design McGraw-Hill

  7. Simplified Forward-Active Region Model(Example 1) • Problem: Estimate terminal currents and base-emitter voltage • Given data: IS =10-16 A,aF = 0.95, VBC = VB - VC = -5 V, IE = 100 mA • Assumptions: Simplified transport model assumptions, room temperature operation, VT = 25.0 mV • Analysis: Current source forward-biases base-emitter diode, VBE > 0, VBC < 0, we know that transistor is in forward-active operation region. Microelectronic Circuit Design McGraw-Hill

  8. Simplified Forward-Active Region Model (Example 2) • Problem: Estimate terminal currents, base-emitter and base-collector voltages. • Given data: IS = 10-16 A,aF = 0.95, VC = +5 V, IB = 100 mA • Assumptions: Simplified transport model assumptions, room temperature operation, VT = 25.0 mV • Analysis: Current source causes base current to forward-bias base-emitter diode, VBE > 0, VBC <0, we know that transistor is in forward-active operation region. Microelectronic Circuit Design McGraw-Hill

  9. Simplified Circuit Model for Forward-Active Region Microelectronic Circuit Design McGraw-Hill

  10. Microelectronic Circuit Design McGraw-Hill

  11. Microelectronic Circuit Design McGraw-Hill

  12. Microelectronic Circuit Design McGraw-Hill

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