Peng Zheng 1 Game Plan for IV Derivation Solve the minoritycarrier diffusion equation in each quasineutral region to obtain excess minoritycarrier profiles different set of boundary conditions for each region ID: 759733
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Slide1
EE130/230A Discussion 14
Peng Zheng
1
Slide2“Game Plan” for I-V Derivation
Solve the minority-carrier diffusion equation in each quasi-neutral region to obtain excess minority-carrier profilesdifferent set of boundary conditions for each regionFind minority-carrier diffusion currents at depletion region edgesAdd hole & electron components together terminal currents
EE130/230A Fall 2013
Lecture 26, Slide
2
Slide3BJT Terminal Currents
We know:Therefore:
EE130/230A Fall 2013
Lecture 26, Slide
3
Slide4BJT 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
Slide5Ebers-Moll Model
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
increasing
(npn) or
VEC (pnp)
EE130/230A Fall 2013
Lecture 26, Slide 5
C. C. Hu,
Modern Semiconductor Devices for Integrated Circuits
, Figure 8-2
Slide6If only VEB is applied (VCB = 0):
If only
V
CB is applied (VEB = 0): :
a
R
: reverse common base gainaF : forward common base gain
I
C
V
CB
V
EB
I
B
E
B
C
Reciprocity relationship
:
EE130/230A Fall 2013
Lecture 26, Slide
6
Slide7In the general case, both
V
EB and VCB are non-zero:
IE: E-B diode current + fraction of C-B diode current that makes it to the E-B junction
I
C
: C-B diode current + fraction of E-B diode current that makes it to the C-B junction
Large-signal equivalent circuit for a pnp BJT
EE130/230A Fall 2013
Lecture 26, Slide
7
R. F.
Pierret, Semiconductor Device Fundamentals, Fig. 11.3
Slide8High gain (bdc >> 1) One-sided emitter junction, so emitter efficiency g 1Emitter doped much more heavily than base (NE >> NB) Narrow base, so base transport factor aT 1Quasi-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)
Summary: BJT Performance Requirements
EE130/230A Fall 2013
Lecture 26, Slide
8
Slide9Questions regarding the MOSFET design project?
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Good luck to Quiz#6!