Lecture%206.pdf - Lecture 6 ANNOUNCEMENTS HW#3 Prob 2...

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Lecture 6 OUTLINE ANNOUNCEMENTS HW#3, Prob. 2 : Re-draw I-V plots for W B reduced by a factor of 2. In case of a major earthquake: Try to duck/crouch on the floor in front of the seats for cover. Once the earthquake stops, evacuate the building in an orderly manner. EE105 Fall 2007 Lecture 6, Slide 1 Prof. Liu, UC Berkeley BJT (cont’d) PNP transistor (structure, operation, models) BJT Amplifiers General considerations Reading: Chapter 4.6-5.1
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Current Flow in a “Long-Base” PN Junction The quasi-neutral N-type and P-type regions have low resistivity, whereas the depletion region has high resistivity. When an external voltage V D is applied across the diode, almost all of this voltage is dropped across the depletion region . J tot EE105 Fall 2007 Lecture 6, Slide 2 Prof. Liu, UC Berkeley x 0 a -b p n n p A D p D p n A n x p n D D L L N N L N D L N D J J = = = 0 E x A relatively small E -field exists in the quasi-neutral regions barb2right drift current
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Review of BJT Operation (Active Mode) The emitter junction is forward biased. barb2right Carriers diffuse across the emitter junction; thus, minority-carrier concentrations are enhanced (by ) at the edges of the emitter-junction depletion region. More minority carriers are “injected” into the base vs. emitter, because the emitter is more heavily doped than the base. The collector junction is reverse biased (or not strongly forward biased) . barb2right Minority-carrier concentrations are ~0 (since ) at the edges of the T D V V e / 0 / V V e EE105 Fall 2007 Lecture 6, Slide 3 Prof. Liu, UC Berkeley emitter-junction depletion region. The minority-carrier concentration gradient in the quasi-neutral base region (of width W B ) results in minority-carrier diffusion toward the collector junction. If W B is much shorter than the minority-carrier diffusion length, then most of the minority carriers injected from the emitter will reach the collector- junction depletion region, and then drift into the quasi-neutral collector.
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  • Spring '14
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