Lecture #23 QUIZ #3 Results (undergraduate scores only, N = 39) Mean = 22.1; Median = 22; Std.
Download ReportTranscript Lecture #23 QUIZ #3 Results (undergraduate scores only, N = 39) Mean = 22.1; Median = 22; Std.
Lecture #23 QUIZ #3 Results (undergraduate scores only, N = 39) Mean = 22.1; Median = 22; Std. Dev. = 1.995 High = 25; Low = 18 OUTLINE The Bipolar Junction Transistor – Fundamentals – Ideal Transistor Analysis Reading: Chapter 10, 11.1 Spring 2007 EE130 Lecture 23, Slide 1 Base Current Components (Active Bias) The base current consists of majority carriers supplied for 1. 2. 3. Recombination of injected minority carriers in the base Injection of carriers into the emitter Reverse saturation current in collector junction • 4. Reduces | IB | Recombination in the base-emitter depletion region Spring 2007 EMITTER BASE COLLECTOR p-type n-type p-type EE130 Lecture 23, Slide 2 Circuit Configurations Output Characteristics for Common-Emitter Configuration Spring 2007 EE130 Lecture 23, Slide 3 Modes of Operation Common-emitter output characteristics (IC vs. VCE) Mode Emitter Junction Collector Junction CUTOFF reverse bias reverse bias Forward ACTIVE forward bias reverse bias* Reverse ACTIVE reverse bias* forward bias SATURATION forward bias forward bias Spring 2007 EE130 Lecture 23, Slide 4 *or not strongly forward biased BJT Electrostatics • Under normal operating conditions, the BJT may be viewed electrostatically as two independent pn junctions Spring 2007 EE130 Lecture 23, Slide 5 Electrostatic potential, V(x) e Electric field, (x) Charge density, r(x) Spring 2007 EE130 Lecture 23, Slide 6 BJT Performance Parameters (PNP) • Emitter Efficiency: I Ep I Ep I En • Base Transport Factor: T – Decrease (5) relative to (1+2) to increase efficiency I Cp I Ep – Decrease (1) relative to (2) to increase transport factor • Common-Base d.c. Current Gain: dc Spring 2007 EE130 Lecture 23, Slide 7 T Collector Current (PNP) • The collector current is comprised of • Holes injected from emitter, which do not recombine in the base (2) • Reverse saturation current of collector junction (3) IC αdc I E ICB0 where ICB0 is the collector current which flows when IE = 0 I C α dc I C I B I CB 0 α dc I CB 0 IC IB 1 α dc 1 α dc βI B I CE 0 Spring 2007 • Common-Emitter d.c. Current Gain: EE130 Lecture 23, Slide 8 IC dc dc I B 1 dc Summary: BJT Fundamentals • Notation & conventions: IE = IB + IC pnp BJT npn BJT • Electrostatics: – Under normal operating conditions, the BJT may be viewed electrostatically as two independent pn junctions Spring 2007 EE130 Lecture 23, Slide 9 • Performance parameters: – Emitter efficiency – Base transport factor I Ep I Ep I En T I Cp I Ep – Common base d.c. current gain – Common emitter d.c. current gain Spring 2007 EE130 Lecture 23, Slide 10 dc T I Cp IE IC dc dc I B 1 dc Notation (PNP BJT) NE = NAE DE = DN tE = tn LE = LN nE0 = np0 = ni2/NE Spring 2007 NB = NDB DB = DP tB = tp LB = L P pB0 = pn0 = ni2/NB EE130 Lecture 23, Slide 11 NC = NAC DC = DN tC = tn LC = LN nC0 = np0 = ni2/NC Ideal Transistor Analysis • 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 • Evaluate minority-carrier diffusion currents at edges of depletion regions dnE E dx " x"0 I En qAD dnC C dx ' x ' 0 I Cn qAD dp B B dx x 0 I Ep qAD dp B B dx x W I Cp qAD • Add hole & electron components together terminal currents Spring 2007 EE130 Lecture 23, Slide 12 Emitter Region Formulation • Diffusion equation: 0 DE d 2 nE dx "2 tnEE • Boundary Conditions: nE ( x" ) 0 nE ( x" 0) nE 0 (e qVEB / kT 1) Spring 2007 EE130 Lecture 23, Slide 13 Base Region Formulation • Diffusion equation: 0 DB d 2 p B dx 2 p B tB • Boundary Conditions: pB (0) pB 0 (e qVEB / kT 1) pB (W ) pB 0 (e qVCB / kT 1) Spring 2007 EE130 Lecture 23, Slide 14 Collector Region Formulation • Diffusion equation: 0 DC d 2 nC dx '2 tnCC • Boundary Conditions: nC ( x' ) 0 nC ( x' 0) nC 0 (e Spring 2007 qVCB / kT 1) EE130 Lecture 23, Slide 15