Chapter 4 – Bipolar Junction Transistors (BJTs)

1. Chapter 4 – Bipolar Junction Transistors (BJTs) Introduction http://engr.calvin.edu/PRibeiro_WEBPAGE/courses/engr311/311_frames.html

2. Physical Structure and Modes of Operation A simplified structure of the npn transistor.

3. Physical Structure and Modes of Operation A simplified structure of the pnp transistor.

4. Physical Structure and Modes of Operation Mode EBJ CBJ Active Forward Reverse Cutoff Reverse Reverse Saturation Forward Forward

5. Operation of The npn Transistor Active Mode Current flow in an npn transistor biased to operate in the active mode, (Reverse current components due to drift of thermally generated minority carriers are not shown.)

6. Operation of The npn Transistor Active Mode Profiles of minority-carrier concentrations in the base and in the emitter of an npn transistor operating in the active mode; vBE 0 and vCB 0.

7. Operation of The npn Transistor Active Mode The Collector Current The Base Current Physical Structure and Modes of Operation

8. Equivalent Circuit Models Large-signal equivalent-circuit models of the npn BJT operating in the active mode.

9. The Constant n • The Collector-Base Reverse Current • The Structure of Actual Transistors

10. The pnp Transistor Current flow in an pnp transistor biased to operate in the active mode.

11. The pnp Transistor Two large-signal models for the pnp transistor operating in the active mode.

12. Circuit Symbols and Conventions C C B B E E

13. Circuit Symbols and Conventions

14. Example 4.1 C B E

15. Example 4.1

16. Example 4.1

18. Exercise 4.8

19. Exercise 4.9

20. The Graphical Representation of the Transistor Characteristics

21. The Graphical Representation of the Transistor Characteristics Temperature Effect (10 to 120 C)

22. Dependence of ic on the Collector Voltage The iC-vCB characteristics for an npn transistor in the active mode.

23. Dependence of ic on the Collector Voltage

24. Dependence of ic on the Collector Voltage – Early Effect VA – 50 to 100V (a) Conceptual circuit for measuring the iC-vCE characteristics of the BJT. (b) The iC-vCEcharacteristics of a practical BJT.

25. Dependence of ic on the Collector Voltage – Early Effect

26. Nested DC Sweeps

27. Example

28. Example

29. Example

30. Monte Carlo Analysis – Using PSpice

31. Monte Carlo Analysis – Using PSpice

32. Monte Carlo Analysis – Using PSpice

33. Monte Carlo Analysis – Using PSpice Probe Output Ic(Q), Ib(Q), Vce

34. The Transistor As An Amplifier (a) Conceptual circuit to illustrate the operation of the transistor of an amplifier. (b) The circuit of (a) with the signal source vbe eliminated for dc (bias) analysis. The Collector Current and The Transconductance The Base Current and the Input Resistance at the Base The Emitter Current and the Input Resistance at the Emitter

35. The Transistor As An Amplifier Linear operation of the transistor under the small-signal condition: A small signal vbe with a triangular waveform is superimpose din the dc voltage VBE. It gives rise to a collector signal current ic, also of triangular waveform, superimposed on the dc current IC. Ic = gm vbe, where gm is the slope of the ic - vBE curve at the bias point Q.

36. Small-Signal Equivalent Circuit Models Two slightly different versions of the simplified hybrid- model for the small-signal operation of the BJT. The equivalent circuit in (a) represents the BJT as a voltage-controlled current source ( a transconductance amplifier) and that in (b) represents the BJT as a current-controlled current source (a current amplifier).

37. Small-Signal Equivalent Circuit Models Two slightly different versions of what is known as the T model of the BJT. The circuit in (a) is a voltage-controlled current source representation and that in (b) is a current-controlled current source representation. These models explicitly show the emitter resistance rerather than the base resistance r featured in the hybrid- model.

38. Signal waveforms in the circuit of Fig. 4.28.

39. Fig.4.30 Example 4.11: (a) circuit; (b) dc analysis; (c) small-signal model; (d) small-signal analysis performed directly on the circuit.

40. Fig.4.34 Circuit whose operation is to be analyzed graphically.

41. Fig.4.35 Graphical construction for the determination of the dc base current in the circuit of Fig.4.34.

42. Fig. 4.36 Graphical construction for determining the dc collector current IC and the collector-to-emmiter voltage VCE in the circuit of Fig. 4.34.

43. Fig.4.37 Graphical determination of the signal components vbe, ib, ic, and vce when a signal component viis superimposed on the dc voltage VBB(see Fig.4.34).

44. Fig.4.38 Effect of bias-point location on allowable signal swing: Load-line A results in bias point QA with a corresponding VCE which is too close to VCC and thus limits the positive swing of vCE. At the other extreme, load-line B results in an operating point too close to the saturation region, thus limiting the negative swing of vCE.

45. Fig.4.44 The common-emitter amplifier with a resistance Re in the emitter. (a) Circuit. (b) Equivalent circuit with the BJT replaced with its T model (c) The circuit in (b) with ro eliminated.

46. Fig.4.45 The common-base amplifier. (a) Circuit. (b) Equivalent circuit obtained by replacing the BJT with its T model.

47. Fig.4.46 The common-collector or emitter-follower amplifier. (a) Circuit. (b) Equivalent circuit obtained by replacing the BJT with its T model. (c) The circuit in (b) redrawn to show that ro is in parallel with RL.(d) Circuit for determining Ro.

48. A General Large-Signal Model For The BJT: The Ebers-Moll Model ISC > ISE (2-50) An npn resistor and its Ebers-Moll (EM) model. ISC and ISE are the scale or saturation currents of diodes DE (EBJ) and DC (CBJ). More General – Describe Transistor in any mode of operation. Base for the Spice model. Low frequency only

49. A General Large-Signal Model For The BJT: The Ebers-Moll Model

50. A General Large-Signal Model For The BJT: The Ebers-Moll Model – Terminal Currents