1. Bipolar Junction Transistors EE314

2. Chapter 13: Bipolar Junction Transistors 1.History of BJT 2.First BJT 3.Basic symbols and features 4.A little bit of physics… 5.Currents in BJT’ 6.Basic configurations 7.Characteristics

3. Current Flow in BJT pnp BJT 1.Injected h + current from E to B 2. e - injected across the forward-biased EB junction (current from B to E) 3. e - supplied by the B contact for recombination with h + (recombination current) 4. h + reaching the reverse-biased C junction 5,6.Thermally generated e - & h + making up the reverse saturation current of the C junction iEiE -i B -i C -V CE

4. Now, you can try… npn BJT

5. BJTs – Basic configurations

6. npn BJTs – Operation Modes Forward & reverse polarized pn junctions Different operation modes:

7. npn BJTs – Operation Modes When there is no I B current almost no I C flows When I B current flows, I C can flow The device is then a current controlled current device Operational modes can be defined based on V BE and V BC

8. BJT-Basic operation npn BJTpnp BJT (n + ), (p + ) – heavy doped regions; Doping in E>B>C

9. Operation mode: v BE is forward & v BC is reverse The Shockley equation I ES –saturation I (10 -12 -10 -16 A); V T =kT/q -thermal V (26meV) D – diffusion coefficient [cm 2 /s]  – carrier mobility [cm 2 /Vs] The Kirchhoff’s laws It is true regardless of the bias conditions of the junction Useful parameter the common-emitter current gain for ideal BJT  is infinite BJTs – Current & Voltage Relationships Einstein relation

10. Useful parameter the common-base current gain for typical BJT  is ~0.99 The Shockley equation once more If we define the scale current A little bit of math… search for i B Finally… BJTs – Current & Voltage Relationships

11. BJTs – Characteristics Schematic Common-Emitter Input Output V BC V BE If V CE < V BE the B-C junction is forward bias and I C decreases Remember V BE has to be greater than 0.6-07 V Example 13.1

12. BJTs – Load line analysis Common-Emitter Amplifier Input loop if i B =0if v BE =0 smaller v in (t)

13. BJTs – Load line analysis Output loop Common-Emitter Amplifier Example 13.2

14. Circuit with BJTs Our approach: Operating point - dc operating point Analysis of the signals - the signals to be amplified Circuit is divided into: model for large-signal dc analysis of BJT circuit bias circuits for BJT amplifier small-signal models used to analyze circuits for signals being amplified Remember !