115A_1_EE115A_W10-Chap4

115A_1_EE115A_W10-Chap4 - Chapter 4 Physics of Bipolar...

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Chapter 4 Physics of Bipolar Transistors h 4.1 General Considerations h 4.2 Structure of Bipolar Transistor 116 h 4.3 Operation of Bipolar Transistor in Active Mode h 4.4 Bipolar Transistor Models h 4.5 Operation of Bipolar Transistor in Saturation Mode h 4.6 The PNP Transistor
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Bipolar Transistor CH4 Physics of Bipolar Transistors 117 h In the chapter, we will study the physics of bipolar transistor and derive large and small signal models.
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Voltage-Dependent Current Source L in out V KR V V A - = = CH4 Physics of Bipolar Transistors 118 h A voltage-dependent current source can act as an amplifier. h If KR L is greater than 1, then the signal is amplified.
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Voltage-Dependent Current Source with Input Resistance CH4 Physics of Bipolar Transistors 119 h Regardless of the input resistance, the magnitude of amplification remains unchanged.
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Exponential Voltage-Dependent Current Source CH4 Physics of Bipolar Transistors 120 h A three-terminal exponential voltage-dependent current source is shown above. h Ideally, bipolar transistor can be modeled as such.
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Structure and Symbol of Bipolar Transistor CH4 Physics of Bipolar Transistors 121 h Bipolar transistor can be thought of as a sandwich of three doped Si regions. The outer two regions are doped with the same polarity, while the middle region is doped with opposite polarity.
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Injection of Carriers CH4 Physics of Bipolar Transistors 122 h Reverse biased PN junction creates a large electric field that sweeps any injected minority carriers to their majority region. h This ability proves essential in the proper operation of a bipolar transistor.
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Forward Active Region CH4 Physics of Bipolar Transistors 123 h Forward active region: V BE > 0, V BC < 0. h Figure b) presents a wrong way of modeling figure a).
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Accurate Bipolar Representation CH4 Physics of Bipolar Transistors 124 h Collector also carries current due to carrier injection from base.
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Carrier Transport in Base CH4 Physics of Bipolar Transistors 125
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T BE S C T BE B E i n E C V V I I V V W N n qD A I 2 exp 1 exp = - = CH4 Physics of Bipolar Transistors 126 h Applying the law of diffusion, we can determine the charge flow across the base region into the collector. h The equation above shows that the transistor is indeed a voltage-controlled element, thus a good candidate as an amplifier. B
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This note was uploaded on 01/08/2011 for the course EE 115 taught by Professor Kaiser during the Spring '09 term at UCLA.

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115A_1_EE115A_W10-Chap4 - Chapter 4 Physics of Bipolar...

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