Lecture 24 OUTLINE The Bipolar Junction Transistor Ideal
Lecture #24 OUTLINE The Bipolar Junction Transistor – Ideal Transistor Analysis – Ebers-Moll model Reading: Chapter 11. 1 1 Spring 2007 EE 130 Lecture 24, Slide 1
Emitter Region Solution • Diffusion equation: • General solution: • Boundary conditions: • Solution: 2 Spring 2007 EE 130 Lecture 24, Slide 2
Collector Region Solution • Diffusion equation: • General solution: • Boundary conditions: • Solution: 3 Spring 2007 EE 130 Lecture 24, Slide 3
Base Region Solution • Diffusion equation: • General solution: • Boundary conditions: • Solution: 4 Spring 2007 EE 130 Lecture 24, Slide 4
Since we can write as 5 Spring 2007 EE 130 Lecture 24, Slide 5
6 Spring 2007 EE 130 Lecture 24, Slide 6
Terminal Currents • We know: • Therefore: 7 Spring 2007 EE 130 Lecture 24, Slide 7
Simplification • In real BJTs, we make W << LB to achieve high current gain. Then, since we have: 8 Spring 2007 EE 130 Lecture 24, Slide 8
BJT Performance Parameters Assumptions: • emitter junction forward biased, collector junction reverse biased • W << LB 9 Spring 2007 EE 130 Lecture 24, Slide 9
BJT with Narrow Emitter Replace with WE’ if short emitter 10 Spring 2007 EE 130 Lecture 24, Slide 10
Ebers-Moll Model increasing The Ebers-Moll model is a large-signal equivalent circuit which describes both the active and saturation regions of BJT operation. 11 Spring 2007 EE 130 Lecture 24, Slide 11
If only VEB is applied (VCB = 0): V EB V CB IB E B C IC If only VCB is applied (VEB = 0): : a. R : reverse common base gain a. F : forward common base gain Reciprocity relationship: 12 Spring 2007 EE 130 Lecture 24, Slide 12
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 13 Spring 2007 EE 130 Lecture 24, Slide 13
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