review_bipolar_transistor

review_bipolar_transistor - Review 1: Physics of Bipolar...

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1 Review 1: Physics of Bipolar Transistors ¾ General Considerations ¾ Structure of Bipolar Transistor ¾ Operation of Bipolar Transistor in Active Mode ¾ Bipolar Transistor Models ¾ Operation of Bipolar Transistor in Saturation Mode ¾ The PNP Transistor
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ECE304 Review: Bipolar Transistor (Spring 2008) By Brian Ma 2 Bipolar Transistor ¾ In the chapter, we will study the physics of bipolar transistor and derive large and small signal models.
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ECE304 Review: Bipolar Transistor (Spring 2008) By Brian Ma 3 Voltage-Dependent Current Source ¾ A voltage-dependent current source can act as an amplifier. ¾ If KR L is greater than 1, then the signal is amplified. L in out V KR V V A = =
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ECE304 Review: Bipolar Transistor (Spring 2008) By Brian Ma 4 Voltage-Dependent Current Source with Input Resistance ¾ Regardless of the input resistance, the magnitude of amplification remains unchanged.
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ECE304 Review: Bipolar Transistor (Spring 2008) By Brian Ma 5 Exponential Voltage-Dependent Current Source ¾ A three-terminal exponential voltage-dependent current source is shown above. ¾ Ideally, bipolar transistor can be modeled as such.
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ECE304 Review: Bipolar Transistor (Spring 2008) By Brian Ma 6 Structure and Symbol of Bipolar Transistor ¾ 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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ECE304 Review: Bipolar Transistor (Spring 2008) By Brian Ma 7 Injection of Carriers ¾ Reverse biased PN junction creates a large electric field that sweeps any injected minority carriers to their majority region. ¾ This ability proves essential in the proper operation of a bipolar transistor.
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ECE304 Review: Bipolar Transistor (Spring 2008) By Brian Ma 8 Forward Active Region ¾ Forward active region: V BE > 0, V BC < 0. ¾ Figure b) presents a wrong way of modeling figure a).
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ECE304 Review: Bipolar Transistor (Spring 2008) By Brian Ma 9 Accurate Bipolar Representation ¾ Collector also carries current due to carrier injection from base.
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ECE304 Review: Bipolar Transistor (Spring 2008) By Brian Ma 10 Carrier Transport in Base
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ECE304 Review: Bipolar Transistor (Spring 2008) By Brian Ma 11 Collector Current ¾ Applying the law of diffusion, we can determine the charge flow across the base region into the collector. ¾ The equation above shows that the transistor is indeed a voltage-controlled element, thus a good candidate as an amplifier. B E i n E S T BE S C T BE B E i n E C W N n qD A I V V I I V V W N n qD A I 2 2 exp 1 exp = = =
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ECE304 Review: Bipolar Transistor (Spring 2008) By Brian Ma 12 Parallel Combination of Transistors ¾ When two transistors are put in parallel and experience the same potential across all three terminals, they can be thought of as a single transistor with twice the emitter area.
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review_bipolar_transistor - Review 1: Physics of Bipolar...

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