Lecture 4

Lecture 4 - Lecture 4 ANNOUNCEMENT • HW#1 solution HW#2...

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EE105 Fall 2009 Lecture 4, Slide 1 Prof. Salahuddin, UC Berkeley Lecture 4 ANNOUNCEMENT OUTLINE Bipolar Junction Transistor (BJT) General considerations Device structure Operation in active mode I-V characteristics Reading: Chapter 4.1-4.3, 4.4.1, 4.4.2
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EE105 Fall 2009 Lecture 4, Slide 2 Prof. Salahuddin, UC Berkeley 1. Under forward bias, the potential barrier is reduced, so that carriers flow (by diffusion) across the junction. Note that at the point of their origin, these are majority carriers 2. The carriers become minority carriers once they cross the junction; as they diffuse in the quasi-neutral regions, they recombine with majority carriers (supplied by the metal contacts). Drift is negligible due to small electric field. 3. Current increases exponentially with increasing forward bias 4. Under reverse bias, the potential barrier is increased, so that negligible carriers flow across the junction 5. Diffusion is negligible and due to high electric field in the junction, a drift current will flow. But the source of this drift current is minority carriers and hence the amplitude of this current will be very low. Review from the last class   1 / T D V V S D e I I D p p A n n i S N L D N L D Aqn I 2
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EE105 Fall 2009 Lecture 4, Slide 3 Prof. Salahuddin, UC Berkeley Voltage-Dependent Current Source A voltage-dependent current source can be used to amplify a voltage signal. If KR L is greater than 1, then the signal is amplified. L in out V KR V V A
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EE105 Fall 2009 Lecture 4, Slide 4 Prof. Salahuddin, UC Berkeley Voltage-Dependent Current Source with Input Resistance The magnitude of amplification is independent of the input resistance r in .
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EE105 Fall 2009 Lecture 4, Slide 5 Prof. Salahuddin, UC Berkeley Exponential Voltage-Dependent Current Source Ideally, a bipolar junction transistor (BJT) can be modeled as a three-terminal exponential voltage- dependent current source:
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EE105 Fall 2009 Lecture 4, Slide 6 Prof. Salahuddin, UC Berkeley Reverse-Biased PN Junction as a Current Source PN junction diode current is ~independent of the
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Lecture 4 - Lecture 4 ANNOUNCEMENT • HW#1 solution HW#2...

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