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EE130/230A Discussion 14

EE130/230A Discussion 14. Peng Zheng. “Game Plan” for I-V Derivation. Solve the minority-carrier diffusion equation in each quasi-neutral region to obtain excess minority-carrier profiles different set of boundary conditions for each region

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EE130/230A Discussion 14

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  1. EE130/230A Discussion 14 PengZheng

  2. “Game Plan” for I-V Derivation • Solve the minority-carrier diffusion equation in each quasi-neutral region to obtain excess minority-carrier profiles • different set of boundary conditions for each region • Find minority-carrier diffusion currents at depletion region edges • Add hole & electron components together  terminal currents EE130/230A Fall 2013 Lecture 26, Slide 2

  3. BJT Terminal Currents • We know: • Therefore: EE130/230A Fall 2013 Lecture 26, Slide 3

  4. BJT with Narrow Base • In practice, we make W << LB to achieve high current gain. Then, since we have: EE130/230A Fall 2013 Lecture 26, Slide 4 R. F. Pierret, Semiconductor Device Fundamentals, Fig. 11.2

  5. Ebers-Moll Model increasing (npn) or VEC (pnp) C. C. Hu, Modern Semiconductor Devices for Integrated Circuits, Figure 8-2 • The Ebers-Moll model is a large-signal equivalent circuit which describes both the active and saturation regions of BJT operation. • Use this model to calculate IB and IC given VBE and VBC EE130/230A Fall 2013 Lecture 26, Slide 5

  6. V V EB CB I B E B C I C If only VEB is applied (VCB = 0): aR : reverse common base gain aF : forward common base gain If only VCBis applied (VEB = 0): : Reciprocity relationship: EE130/230A Fall 2013 Lecture 26, Slide 6

  7. In the general case, both VEB and VCB are non-zero: IC: C-B diode current + fraction of E-B diode current that makes it to the C-B junction IE: E-B diode current + fraction of C-B diode current that makes it to the E-B junction Large-signal equivalent circuit for a pnp BJT R. F. Pierret, Semiconductor Device Fundamentals, Fig. 11.3 EE130/230A Fall 2013 Lecture 26, Slide 7

  8. Summary: BJT Performance Requirements • High gain (bdc >> 1) • One-sided emitter junction, so emitter efficiency g  1 • Emitter doped much more heavily than base (NE >> NB) • Narrow base, so base transport factor aT 1 • Quasi-neutral base width << minority-carrier diffusion length (W << LB) • IC determined only by IB (IC function of VCE,VCB) • One-sided collector junction, so quasi-neutral base width W does not change drastically with changes in VCE (VCB) • Based doped more heavily than collector (NB > NC) (W = WB – xnEB – xnCB for PNP BJT) EE130/230A Fall 2013 Lecture 26, Slide 8

  9. Questionsregarding the MOSFET design project? Good luck to Quiz#6!

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