Bipolar Junction Transistor

Abstract

The bipolar junction transistor or BJT is a device capable of amplifying a voltage or current, something that diodes are not able to do. This amplifying characteristic makes the BJT suitable for a wide range of applications. The device was invented in 1947 by Walter H. Brattain, John Bardeen and William Shockley who were awarded the Nobel Prize in Physics in 1956 for this invention. It revolutionized the electronics industry by enabling miniaturization of electronic circuits and increased equipment portability. This chapter discusses the characteristics of the BJT and its use in elementary amplifier circuits. At the end of it, the student will be able to:

Problems

• 1. Design a fixed-bias common emitter amplifier with a 24 volt supply and an npn silicon transistor having β = 100. Design for maximum symmetrical swing. Determine the voltage gain and input impedance.

• 2. Draw the load line for the circuit of problem 1, indicating the q point. What does the slope of the line represent?

• 3. Determine the collector current and voltage in the fixed-bias amplifier of Fig. 2.74, assuming transistor current gain of 100. If the transistor is replaced by one with current gain of 75, determine the new collector current and voltage.

  Fig. 2.74

  

  Circuit for Question 3

• 4. Using a DC supply of 15 V, a load resistor of 2 k and a silicon pnp transistor with β = 150 at room temperature, (a) bias the transistor for maximum symmetrical swing using fixed bias and (b) calculate the value ofV_CEq at 50 °C if β goes to 110.

• 5. In the circuit of Fig. 2.75, determine the value of R_B in order to achieve a collector voltage of 10 V, assuming β = 130. Evaluate the input impedance for the circuit.

  Fig. 2.75

  

  Circuit for Question 5

• 6. What are the two main sources of distortion in a common emitter amplifier? Discuss ways by which this distortion can be minimized.

• 7. Design a voltage divider-biased common emitter amplifier for maximum symmetrical swing using a small-signal npn silicon transistor with a current gain of 120 and a 25 volt supply. Justify all steps in your design. Evaluate the voltage gain of your circuit.

• 8. In the common emitter voltage divider-biased-biased amplifier of Fig. 2.76 determine the collector current and the collector voltage.

  Fig. 2.76

  

  Circuit for Question 8

• 9. In the common emitter voltage divider-biased-biased amplifier of Fig. 2.77 using a pnp transistor, determine the collector current, the collector voltage and the emitter voltage.

  Fig. 2.77

  

  Circuit for Question 9

• 10. Design a common emitter amplifier utilizing current feedback biasing using an npn silicon transistor having β = 200 and a 12 volt supply.

• 11. Determine the collector current and voltage for the collector-base feedback circuit shown in Fig. 2.78 assuming β = 100.

  Fig. 2.78

  

  Circuit for Question 11

• 12. Design a common emitter amplifier using a ±20 V bipolar supply and a transistor with β = 150.

• 13. Design a voltage divider-biased common base amplifier using a 28 volt supply and an npn silicon transistor having β = 110. Find the voltage gain and input impedance of the circuit.

• 14. Explain the phase relationship between the input and output voltages in a common base amplifier.

• 15. Design a common base amplifier using fixed bias and a silicon npn transistor having β = 100. Use V_CC = 18 volts.

• 16. Design a common base amplifier using a bipolar supply ±20 V. Determine the voltage gain and input impedance.

• 17. Design a common base amplifier for maximum symmetrical swing using a small-signal pnp silicon transistor with a current gain of 125 and a 20 volt supply. Use a 3.3 V Zener to fix the base voltage. Justify all your design steps. Evaluate the input impedance and voltage gain of your circuit.

• 18. Design a voltage divider-biased-biased common collector amplifier for maximum symmetrical swing using a small-signal pnp silicon transistor with a current gain of 110 and a 22 volt supply. Justify all your design steps. Evaluate the input impedance and voltage gain of your circuit.

• 19. Design a voltage divider-biased-biased common collector amplifier for maximum symmetrical swing using a small-signal npn silicon transistor with a current gain of 125 and a 32 volt supply. Justify all your design steps. Determine the input impedance of your circuit.

• 20. Design a common collector fixed-bias amplifier using a 22 volt supply and a general purpose npn silicon transistor having β = 180.

• 21. Evaluate the collector current and voltage in the common base amplifier of Fig.

  Fig. 2.79

  

  Circuit for Question 21

  2.79.

• 22. Using the configuration of bench supply, design a regulated power supply giving 5 volts at 150 mA with electronic short-circuit protection.

• 23. Design a common collector amplifier using a pnp silicon transistor with a ±15 V supply.

• 24. Determine the collector current and voltage in the common collector circuit

  Fig. 2.80

  

  Circuit for Question 24

  of Fig. 2.80.