1. LARGE-SIGNAL BEHAVIOR OF BJTS Large-signal models in the forward-active region Effects of collector voltage in the forward-active region Ohmic and inverse active regions Transistor breakdown voltages Dependence of transistor current gain on operation conditions (saturation)

2. Bipolar Junction Transistor (BJT) One diode...Why not another diode

3. Bipolar Junction Transistor (BJT) What happens when we combine them?

4. NPN Bipolar Junction Transistor BJT = Bipolar Junction Transistor Collector (C) Emitter (E) Base (B)

5. Carrier Transport in a BJT

6. BJT Band Diagram V bi + V cb V bi + V eb V eb > 0 Base Width (W) Emitter BaseCollector Forward-Active Region of Operation EfEf

7. BJT Current Equations Electrons and Holes recombine in the base region at a rate . Typically,  is limited by this recombination (looks like a saturated subthreshold MOSFET) No recombination Recombination Base Width (W)

8. Forward-Active Region of a BJT EmitterBaseCollector 0W Carrier Concentration E-B Depletion Region C-B Depletion Region n e0 e V BE /U T V BE > 0 (Forward Biased), V BC < 0 (Reversed Biased)

9. Forward-Active Region of a BJT EmitterBaseCollector 0W Carrier Concentration E-B Depletion Region C-B Depletion Region n e0 e V BE /U T I C = I C0 e I B = I C /  f V BE /U T d 2 n dx 2 + = 0 nnnn dn dx I C = q A D n W << L n

10. Gummel Plots 0.10.20.30.40.50.60.7 10 -12 10 -11 10 -10 10 -9 10 -8 10 -7 10 -6 10 -5 Base-Emitter Voltage (V) Currents Ic: n=1, Is = 5.52fA Ib: n=1.019, Is = 0.048fA

11. Gummel Plot:  depends on I c

12. Current gain changes Region II: Midcurrent region where  F is approximately constant Region III: High current region where  F decreases as i C increases Region I: Low current region where  F decreases as i C decreases

13. Large-Signal Modeling (sort of) Does not incorporate the Early effect

14. Reverse-Active Region of a BJT EmitterBaseCollector 0W Carrier Concentration E-B Depletion Region C-B Depletion Region n c0 e V BC /U T V BC > 0 (Forward Biased), V BE < 0 (Reversed Biased) I E = I E0 e I B = I C /  R V BC /U T

15. Ohmic Region of a BJT This region is often called saturation ^ Incorrectly EmitterBaseCollector 0W Carrier Concentration E-B Depletion Region C-B Depletion Region n e0 e V BE /U T n c0 e V BC /U T V BC > 0 (Forward Biased), V BE > 0 (Forward Biased)

16. Ebers-Moll Model of a BJT EmitterBaseCollector 0W Carrier Concentration E-B Depletion Region C-B Depletion Region n e0 e V BE /U T n c0 e V BC /U T I C = I C0 ( e - 1 ) - I E0 ( e - 1 ) = I C0 e ( ( e - (I E0 / I C0 ) e ) + I C0 - I E0 V BE /U T V BC /U T V B /U T -V E /U T -V c /U T

17. Ohmic and Active BJT Regions -V CE /U T I C = (I C0 - I E0 ) + I C0 e ( 1 - (I E0 /  R I C0 ) e ) V BE /U T 00.511.522.533.544.55 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 Collector voltage (V) Collector current (  A) V CE (sat)

18. Simplified Ohmic Model In ohmic, both junctions are forward biased and the impedance levels looking into the emitter or collector is very low. V BE (on)  0.6 to 0.7V and V CE (sat)  0.2V

19. TRANSISTOR BREAKDOWN VOLTAGES Common-Base Transistor Breakdown Characteristics

20. BJT Breakdown Characteristics