Spring 2007EE130 Lecture 24, Slide 1 Lecture #24 HW#8 ANNOUNCEMENTS Start Problem 4 early! Note that Problem 3f has been revised OUTLINE The Bipolar Junction Transistor –Ideal Transistor Analysis –Ebers-Moll model Reading: Chapter 11.1

Spring 2007EE130 Lecture 24, Slide 2 Emitter Region Solution Diffusion equation: General solution: Boundary conditions: Solution:

Spring 2007EE130 Lecture 24, Slide 3 Collector Region Solution Diffusion equation: General solution: Boundary conditions: Solution:

Spring 2007EE130 Lecture 24, Slide 4 Base Region Solution Diffusion equation: General solution: Boundary conditions: Solution:

Spring 2007EE130 Lecture 24, Slide 5 Since we can write as

Spring 2007EE130 Lecture 24, Slide 6

Spring 2007EE130 Lecture 24, Slide 7 Terminal Currents We know: Therefore:

Spring 2007EE130 Lecture 24, Slide 8 Simplification In real BJTs, we make W << L B to achieve high current gain. Then, since we have:

Spring 2007EE130 Lecture 24, Slide 9 BJT Performance Parameters Assumptions: emitter junction forward biased, collector junction reverse biased W << L B

Spring 2007EE130 Lecture 24, Slide 10 BJT with Narrow Emitter Replace with W E ’ if short emitter

Spring 2007EE130 Lecture 24, Slide 11 The Ebers-Moll model is a large-signal equivalent circuit which describes both the active and saturation regions of BJT operation. Ebers-Moll Model increasing

Spring 2007EE130 Lecture 24, Slide 12 If only V EB is applied (V CB = 0): If only V CB is applied (V EB = 0): :  R : reverse common base gain  F : forward common base gain I C V CB V EB I B E BC Reciprocity relationship:

Spring 2007EE130 Lecture 24, Slide 13 In the general case, both V EB and V CB are non-zero: I E : 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