1. Chapter 6. Bipolar Junction Transistors (BJTs)

2. Bipolar Junction Transistor Three terminal device Voltage between two terminals to control current flow in third terminal Invented in 1948 at Bell Telephone Laboratories Dominant until late 1980’s Reliable under harsh operating conditions –High frequency applications –High speed designs –High power applications

3. npn transistor n-type emitter (E) region, p-type base (B) region, n-type collector (C) region Two pn junctions (naming basis for bipolar junction transistor) Modes -Active: used for amplifier design -Cutoff -Saturation: used for logic design -Reverse active: limited operation

4. pnp transistor – dual of npn transistor

5. Active Mode of npn Transistor

8. Circuit Models for Active Mode npn Transistor

9. Practical Implementation E and C are not symmetrical. pnp transistors works dual to npn transistors much in the same way PMOSFET works dual to NMOSFET. (In this class, we will concentrate on npn transistors.)

10. Circuit Symbols for npn Transistors Biasing in active mode Directions of current flow

12. i C – v BE Characteristics Temperature Dependence

13. Common Base Characteristics Base voltage is fixed at zero. In active region, v CB ≥ - 0.4 V

14. Dependence of i C on Collector Voltage

15. Circuit Models with Output Resistance r o

16. Common Emitter Configuration

18. Common Emitter Saturation Model

19. Designing Linear Amplifiers (Active Region)

20. Amplifier Gain

22. Graphical Analysis

24. To determine i B, i C and v CE, you need to use both graphs.

25. Quiescent point must be selected to give a symmetric output swing.

32. Input part + _ V BB _ + 10 V R B1 R B2 10 VR B2 V BB R B1 + _ V BB R BB

34. Biasing BJT Determining a quiescent point for linearization Active mode operation Considerations –Stable with respect to manufacturing parameters (e.g., r o, β) –Desired gains –Acceptable output swing

35. Biasing with Single Power Supply Fix V BE or I B. Output directly depends on β Unstable with respect to temperature variation

36. Addition of Degeneration Resistor

38. Biasing with Two Power Supplies

39. Biasing with Feedback Resistor

40. Biasing with Current Source

41. Small Signal Analysis A quiescent point has been determined by biasing. Active mode operation –Forward biasing for base-emitter junction by V BE –Reverse biasing for collector-base junction by R C and V CC

44. The transistor performs as a voltage controlled current source with gain g m when input varies by 10 mV or less.

48. Hybrid π Model Short circuit voltage sources Open circuit current sources Short circuit capacitors

50. T Model

54. Hybrid π Model with Early Effect

55. Structure of Single Stage Amplifier

56. Common Emitter Amplifier

59. Common Emitter Amplifier with R E

62. Common Base Amplifier

65. Common Collector Amplifier

69. Digital Logic Inverter Transistor is in saturation mode. Logic 1: v I ≈ V CC → v O =V CEsat ≈ 0.2 V Logic 0: v I ≈ 0 → v O =V CC

70. v I – v O Transfer Function V CC = 5 V R B = 10 kΩ R C = 1 kΩ β = 50