Bipolar Junction Transistors 1.docx

Bipolar Junction Transistors (BJTs) 1. A transistor has how many doped regions?  a. 1  b. 2  c. 3  d. 4 2. What is one important thing transistors do?  a. Amplify weak signals  b. Rectify line voltage  C. Regulate voltage  d. Emit light 3. Who invented the first junction transistor?  a. Bell  b. Faraday  c. Marconi  d. Schockley 4. In an npn transistor, the majority carriers in the base are  a. Free electrons  b. Holes  c. Neither  d. Both 5. The barrier potential across each silicon depletion layer is  a. 0  b. 0.3 V  c. 0.7 V  d. 1 V 6. The emitter diode is usually  a. Forward-biased  b. Reverse-biased  c. Nonconducting  d. Operating in the breakdown region 7. For normal operation of the transistor, the collector diode has to be  a. Forward-biased  b. Reverse-biased  c. Nonconducting  d. Operating in the breakdown region 8. The base of an npn transistor is thin and  a. Heavily doped  b. Lightly doped  c. Metallic  d. Doped by a pentavalent material 9. Most of the electrons in the base of an npn transistor flow  a. Out of the base lead  b. Into the collector  c. Into the emitter  d. Into the base supply 10. Most of the electrons in the base of an npn transistor do not recombine because they  a. Have a long lifetime  b. Have a negative charge  c. Must flow a long way through the base  d. Flow out of the base 11. Most of the electrons that flow through the base will  a. Flow into the collector  b. Flow out of the base lead

 c. Recombine with base holes  d. Recombine with collector holes 12. The current gain of a transistor is the ratio of the  a. Collector current to emitter current  b. Collector current to base current  c. Base current to collector current  d. Emitter current to collector current 13. Increasing the collector supply voltage will increase  a. Base current  b. Collector current  c. Emitter current  d. None of the above 14. The fact that only a few holes are in the base region means the base is  a. Lightly doped  b. Heavily doped  c. Undoped  d. None of the above 15. In a normally biased npn transistor, the electrons in the emitter have enough energy to overcome the barrier potential of the  a. Base-emitter junction  b. Base-collector junction  c. Collector-base junction  d. Recombination path 16. When a free electron recombines with a hole in the base region, the free electron becomes  a. Another free electron  b. A valence electron  c. A conduction-band electron  d. A majority carrier 17. What is the most important fact about the collector current?  

a. It is measured in milliamperes. b. It equals the base current divided by the current gain.  c. It is small.  d. It approximately equals the emitter current. 18. If the current gain is 200 and the collector current is 100 mA, the base current is  a. 0.5 mA  b. 2 mA  c. 2 A  d. 20 A 19. The base-emitter voltage is usually  a. Less than the base supply voltage  b. Equal to the base supply voltage  c. More than the base supply voltage  d. Cannot answer 20. The collector-emitter voltage is usually

  

a. Less than the collector supply voltage b. Equal to the collector supply voltage c. More than the collector supply voltage  d. Cannot answer 21. The power dissipated by a transistor approximately equals the collector current times  a. Base-emitter voltage  b. Collector-emitter voltage  c. Base supply voltage  d. 0.7 V 22. A small collector current with zero base current is caused by the leakage current of the  a. Emitter diode  b. Collector diode  c. Base diode  d. Transistor 23. A transistor acts like a diode and a  a. Voltage source  b. Current source  c. Resistance  d. Power supply 24. If the base current is 100 mA and the current gain is 30, the collector current is  a. 300 mA  b. 3 A  c. 3.33 A  d. 10 A 25. The base-emitter voltage of an ideal transistor is  a. 0  b. 0.3 V  c. 0.7 V  d. 1 V 26. If you recalculate the collector-emitter voltage with the second approximation, the answer will usually be  a. Smaller than the ideal value  b.. The same as the ideal value  c. Larger than the ideal value  d. Inaccurate 27. In the active region, the collector current is not changed significantly by  a. Base supply voltage  b. Base current  c. Current gain  d. Collector resistance 28. The base-emitter voltage of the second approximation is 

a. 0

 b. 0.3 V  c. 0.7 V  d. 1 V 29. If the base resistor is open, what is the collector current?    

a. 0 b. 1 mA c. 2 mA d. 10 mA

ANSWERS: 1. c. 3 2. a. Amplify weak signals 3. d. Schockley 4. b. Holes 5. c. 0.7 V 6. a. Forward-biased 7. b. Reverse-biased 8. b. Lightly doped 9. b. Into the collector 10. a. Have a long lifetime 11. a. Flow into the collector 12. b. Collector current to base current 13. d. None of the above 14. a. Lightly doped 15. a. Base-emitter junction 16. b. A valence electron 17. d. It approximately equals the emitter current. 18. a. 0.5 mA 19. a. Less than the base supply voltage 20. a. Less than the collector supply voltage 21. b. Collector-emitter voltage 22. b. Collector diode 23. b. Current source 24. b. 3 A 25. a. 0 26. c. Larger than the ideal value 27. d. Collector resistance 28. c. 0.7 V 29. a. 0 Transistor Fundamentals 1. The current gain of a transistor is defined as the ratio of the collector current to the  a. Base current  b. Emitter current  c. Supply current  d. Collector current 2. The graph of current gain versus collectorcurrent indicates that the current gain  a. Is constant  b. Varies slightly  c. Varies significantly  d. Equals the collector current divided by the base current 3. When the collector current increases, what does the current gain do?  a. Decreases  b. Stays the same

 c. Increases  d. Any of the above 4. As the temperature increases, the current gain  a. Decreases  b. Remains the same  c. Increases  d. Can be any of the above 5. When the base resistor decreases, the collector voltage will probably  a. Decrease  b. Stay the same  c. Increase  d. Do all of the above 6. If the base resistor is very small, the transistor will operate in the  a. Cutoff region  b. Active region  c. Saturation region  d. Breakdown region 7. Ignoring the bulk resistance of the collector diode, the collector-emitter saturation voltage is  a. 0  b. A few tenths of a volt  C. 1 V  d. Supply voltage 8. Three different Q points are shown on a load line. The upper Q point represents the  a. Minimum current gain  b. Intermediate current gain  c. Maximum current gain  d. Cutoff point 9. If a transistor operates at the middle of the load line, an increase in the base resistance will move the Q point  a. Down  b. Up  c. Nowhere  d. Off the load line 10. If a transistor operates at the middle of the load line, an increase in the current gain will move the Q point  a. Down  b. Up  c. Nowhere  d. Off the load line 11. If the base supply voltage increases, the Q point moves  a. Down  b. Up  c. Nowhere  d. Off the load line 12. Suppose the base resistor is open. The Q point will be  a. In the middle of the load line  b. At the upper end of the load line  c. At the lower end of the load line  d. Off the load line 13. If the base supply voltage is disconnected, the collector emitter voltage will equal

 a. 0 V  b. 6 V  c. 10.5 V  d. Collector supply voltage 14. If the base resistor is shorted, the transistor will probably be  a. Saturated  b. In cutoff  c. Destroyed  d. None of the above 15. If the collector resistor decreases to zero in a base-biased circuit, the load line will become  a. Horizontal  b. Vertical  c. Useless  d. Flat 16. The collector current is 10 mA. If the current gain is 100, the base current is  a. 1 microamp  b. 10 microamp  c. 100 microamp  d. 1 mA 17. The base current is 50 microamp. If the current gain is 125, the collector current is closest in value to  a. 40 microamp  b. 500 microamp  c. 1 mA  d. 6 mA 18. When the Q point moves along the load line, the voltage increases when the collector current  a. Decreases  b. Stays the same  c. Increases  d. Does none of the above 19. When there is no base current in a transistor switch, the output voltage from the transistor is  a. Low  b. High  c. Unchanged  d. Unknown 20. A circuit with a fixed emitter current is called  a. Base bias  b. Emitter bias  c. Transistor bias  d. Two-supply bias 21. The first step in analyzing emitter-based circuits is to find the  a. Base current  b. Emitter voltage  c. Emitter current  d. Collector current 22. If the current gain is unknown in an emitter-biased circuit, you cannot calculate the  a. Emitter voltage  b. Emitter current

 c. Collector current  d. Base current 23. If the emitter resistor is open, the collector voltage is  a. Low  b. High  c. Unchanged  d. Unknown 24. If the collector resistor is open, the collector voltage is  a. Low  b. High  c. Unchanged  d. Unknown 25. When the current gain increases from 50 to 300 in an emitter-biased circuit, the collector current  a. Remains almost the same  b. Decreases by a factor of 6  c. Increases by a factor of 6  d. Is zero 26. If the emitter resistance decreases, the collector voltage  a. Decreases  b. Stays the same  c. Increases  d. Breaks down the transistor 27. If the emitter resistance decreases, the  a. Q point moves up  b. Collector current decreases  c. Q point stays where it is  d. Current gain increases

ANSWERS: 1. a. Base current 2. c. Varies significantly 3. d. Any of the above 4. d. Can be any of the above 5. a. Decrease 6. c. Saturation region 7. a. 0 8. c. Maximum current gain 9. a. Down 10. b. Up 11. b. Up 12. c. At the lower end of the load line 13. d. Collector supply voltage 14. c. Destroyed 15. b. Vertical 16. c. 100 microamp 17. d. 6 mA 18. a. Decreases 19. b. High 20. b. Emitter bias 21. b. Emitter voltage 22. d. Base current 23. b. High 24. a. Low 25. a. Remains almost the same

26. a. Decreases 27. a. Q point moves up

9. The collector voltage of a VDB circuit is not sensitive to changes in the

Transistor Biasing

 a. Supply voltage  b. Emitter resistance  c. Current gain  d. Collector resistance 10. If the emitter resistance increases in a VDB circuit, the collector voltage

1. For emitter bias, the voltage across the emitter resistor is the same as the voltage between the emitter and the  a. Base  b. Collector  c. Emitter  d. Ground 2. For emitter bias, the voltage at the emitter is 0.7 V less than the

 a. Decreases  b. Stays the same  c. Increases  d. Doubles 11. Base bias is associated with

 a. Base voltage  b. Emitter voltage  c. Collector voltage  d. Ground voltage 3. With voltage-divider bias, the base voltage is

 a. Amplifiers  b. Switching circuits  c. Stable Q point  d. Fixed emitter current 12. If the emitter resistance doubles in a VDB circuit, the collector current will

   

a. Less than the base supply voltage b. Equal to the base supply voltage c. Greater than the base supply voltage d. Greater than the collector supply voltage 4. VDB is noted for its

 a. Double  b. Drop in half  c. Remain the same  d. Increase 13. If the collector resistance increases in a VDB circuit, the collector voltage will

 a. Unstable collector voltage  b. Varying emitter current  c. Large base current  d. Stable Q point 5. With VDB, an increase in emitter resistance will

 a. Decrease  b. Stay the same  c. Increase  d. Double 14. The Q point of a VDB circuit is 

 a. Decrease the emitter voltage  b. Decrease the collector voltage  c. Increase the emitter voltage  d. Decrease the emitter current 6. VDB has a stable Q point like  a. Base bias  b. Emitter bias  c. Collector-feedback bias  d. Emitter-feedback bias 7. VDB needs  a. Only three resistors  b. Only one supply  c. Precision resistors  d. More resistors to work better 8. VDB normally operates in the    

a. Active region b. Cutoff region c. Saturation region d. Breakdown region

a. Hypersensitive to changes in current gain  b. Somewhat sensitive to changes in current gain  c. Almost totally insensitive to changes in current gain  d. Greatly affected by temperature changes 15. The base voltage of two supply emitter bias (TSEB) is  a. 0.7 V  b. Very large  c. Near 0 V  d. 1.3 V 16. If the emitter resistance doubles with TSEB, the collector current will  a. Drop in half  b. Stay the same  c. Double  d. Increase 17. If a splash of solder shorts the collector resistor of TSEB, the collector voltage will

 a. Drop to zero  b. Equal the collector supply voltage  C. Stay the same  d. Double 18. If the emitter resistance increases with TSEB, the collector voltage will  a. Decrease  b. Stay the same  C. Increase  d. Equal the collector supply voltage 19. If the emitter resistor opens with TSEB, the collector voltage will  a. Decrease  b. Stay the same  c. Increase slightly  d. Equal the collector supply voltage 20. In TSEB, the base current must be very  a. Small  b. Large  c. Unstable  d. Stable 21. The Q point of TSEB does not depend on the  a. Emitter resistance  b. Collector resistance  c. Current gain  d. Emitter voltage 22. The majority carriers in the emitter of a PNP transistor are  a. Holes  b. Free electrons  c. Trivalent atoms  d. Pentavalent atoms 23. The current gain of a PNP transistor is  

a. The negative of the NPN current gain b. The collector current divided by the emitter current  c. Near zero  d. The ratio of collector current to base current 24. Which is the largest current in a PNP transistor?  a. Base current  b. Emitter current  c. Collector current  d. None of these 25. The currents of a PNP transistor are    

a. Usually smaller than NPN currents b. Opposite NPN currents c. Usually larger than NPN currents d. Negative

26. With PNP voltage-divider bias, you must use    

a. Negative power supplies b. Positive power supplies c. Resistors d. Grounds

ANSWERS: 1. d. Ground 2. a. Base voltage 3. a. Less than the base supply voltage 4. d. Stable Q point 5. d. Decrease the emitter current 6. b. Emitter bias 7. b. Only one supply 8. a. Active region 9. c. Current gain 10. c. Increases 11. b. Switching circuits 12. b. Drop in half 13. a. Decrease 14. c. Almost totally insensitive to changes in current gain 15. c. Near 0 V 16. a. Drop in half 17. b. Equal the collector supply voltage 18. C. Increase 19. d. Equal the collector supply voltage 20. a. Small 21. c. Current gain 22. a. Holes 23. d. The ratio of collector current to base current 24. b. Emitter current 25. b. Opposite npn currents 26. c. Resistors Junction Field Effect Transistor (JFETs) 1. A JFET  a. Is a voltage-controlled device  b. Is a current-controlled device  c. Has a low input resistance  d. Has a very large voltage gain 2. A unipolar transistor uses  a. Both free electrons and holes  b. Only free electrons  c. Only holes  d. Either one or the other, but not both 3. The input impedance of a JFET  a. Approaches zero  b. Approaches one  c. Approaches infinity  d. Is impossible to predict 4. The gate controls  a. The width of the channel  b. The drain current  c. The proportional pinch-off voltage  d. All the above

5. The gate-source diode of a JFET should be  a. Forward-biased  b. Reverse-biased  c. Either forward- or reverse biased  d. None of the above 6. Compared to a bipolar transistor, the JFET has a much higher  a. Voltage gain  b. Input resistance  c. Supply voltage  d. Current 7. The pinch-off voltage has the same magnitude as the  a. Gate voltage  b. Drain-source voltage  c. Gate-source voltage  d. Gate-source cutoff voltage 8. When the drain saturation current is less than IDSS, a JFET acts like a  a. Bipolar transistor  b. Current source  c. Resistor  d. Battery 9. RDS equals pinch-off voltage divided by the  a. Drain current  b. Gate current  c. Ideal drain current  d. Drain current for zero gate voltage 10. The transconductance curve is  a. Linear  b. Similar to the graph of a resistor  c. Nonlinear  d. Like a single drain curve 11. The transconductance increases when the drain current approaches  a. 0  b. ID(sat)  c. IDSS  d. IS 12. A CS amplifier has a voltage gain of  a. gmrd  b. gmrs  c. gmrs/(l + gmrs)  d. gmrd/(l + gmrd) 13. A source follower has a voltage gain of  a. gmrd  b. gmrs  c. gmrs/(l + gmrs)  d. gmrd/(l + gmrd) 14. When the input signal is large, a source follower has  a. A voltage gain of less than one  b. A small distortion  c. A high input resistance  d. All of these 15. The input signal used with a JFET analog switch should be  a. Small  b. Large  c. A square wave  d. Chopped

16. A cascode amplifier has the advantage of  a. Large voltage gain  b. Low input capacitance  c. Low input impedance  d. Higher gm 17. VHF stands for frequencies from  a. 300 kHz to 3 MHz  b. 3 to 30 MHz  c. 30 to 300 MHz  d. 300 MHz to 3 GHz 18. When a JFET is cut off, the depletion layers are  a. Far apart  b. Close together  c. Touching  d. Conducting 19. When the gate voltage becomes more negative in an N channel JFET, the channel between the depletion layers  a. Shrinks  b. Expand  c. Conduct  d. Stop conducting 20. If a JFET has IDSS = 10 mA and VP = 2 V, then RDS equals  a. 200 ohm  b. 400 ohm  c. 1 kohm  d. 5 kohm 21. The easiest way to bias a JFET in the ohmic region is with  a. Voltage-divider bias  b. Self-bias  c. Gate bias  d. Source bias 22. Self-bias produces  a. Positive feedback  b. Negative feedback  c. Forward feedback  d. Reverse feedback 23. To get a negative gate-source voltage in a self-biased JFET circuit, you must have a  a. Voltage divider  b. Source resistor  c. Ground  d. Negative gate supply voltage 24. Transconductance is measured in  a. Ohms  b. Amperes  c. Volts  d. Mhos or Siemens 25. Transconductance indicates how effectively the input voltage controls the  a. Voltage gain  b. Input resistance  c. Supply voltage  d. Output current

ANSWERS: 1. a. Is a voltage-controlled device 2. d. Either one or the other, but not both 3. c. Approaches infinity 4. d. All the above 5. b. Reverse-biased 6. b. Input resistance 7. d. Gate-source cutoff voltage 8. c. Resistor 9. d. Drain current for zero gate voltage 10. c. Nonlinear 11. c. IDSS 12. a. gmrd 13. c. gmrs/(l + gmrs) 14. d. All of these 15. a. Small 16. b. Low input capacitance 17. c. 30 to 300 MHz 18. c. Touching 19. a. Shrinks 20. a. 200 ohm 21. a. Voltage-divider bias 22. b. Negative feedback 23. b. Source resistor 24. d. Mhos or Siemens 25. d. Output current Metal Oxide Semiconductor Field Effect Transistor (MOSFETs) 1. Which of the following devices revolutionized the computer industry?  a. JFET  b. D-MOSFET  c. E-MOSFET  d. Power FET 2. The voltage that turns on an EMOS device is the  a. Gate-source cutoff voltage  b. Pinch-off voltage  c. Threshold voltage  d. Knee voltage 3. Which of these may appear on the data sheet of an enhancement-mode MOSFET?  a. VGS(th)  b. ID(on)  c. VGS(on)  d. All of the above 4. The VGS(on) of an n-channel E-MOSFET is  

a. Less than the threshold voltage b. Equal to the gate-source cutoff voltage  c. Greater than VDS(on)  d. Greater than VGS(th) 5. An ordinary resistor is an example of  

a. A three-terminal device b. An active load

 c. A passive load  d. A switching device 6. An E-MOSFET with its gate connected to its drain is an example of  a. A three-terminal device  b. An active load  c. A passive load  d. A switching device 7. An E-MOSFET that operates at cutoff or in the ohmic region is an example of  a. A current source  b. An active load  c. A passive load  d. A switching device 8. CMOS stands for  a. Common MOS  b. Active-load switching  c. p-channel and n-channel devices  d. Complementary MOS 9. VGS(on) is always  a. Less than VGS(th)  b. Equal to VDS(on)  c. Greater than VGS(th)  d. Negative 10. With active-load switching, the upper EMOSFET is a  a. Two-terminal device  b. Three-terminal device  c. Switch  d. Small resistance 11. CMOS devices use  a. Bipolar transistors  b. Complementary E-MOSFETs  c. Class A operation  d. DMOS devices 12. The main advantage of CMOS is its  a. High power rating  b. Small-signal operation  c. Switching capability  d. Low power consumption 13. Power FETs are  a. Integrated circuits  b. Small-signal devices  c. Used mostly with analog signals  d. Used to switch large currents 14. When the internal temperature increases in a power FET, the   

a. Threshold voltage increases b. Gate current decreases c. Drain current decreases

 d. Saturation current increases 15. Most small-signal E-MOSFETs are found in  a. Heavy-current applications  b. Discrete circuits  c. Disk drives  d. Integrated circuits 16. Most power FETS are  a. Used in high-current applications  b. Digital computers  c. RF stages  d. Integrated circuits 17. An n-channel E-MOSFET conducts when it has  a. VGS > VP  b. An N-Type inversion layer  c. VDS > 0  d. Depletion layers 18. With CMOS, the upper MOSFET is  a. A passive load  b. An active load  c. Nonconducting  d. Complementary 19. The high output of a CMOS inverter is  a. VDD/2  b. VGS  c. VDS  d. VDD 20. The RDS(on) of a power FET    

a. Is always large b. Has a negative temperature coefficient c. Has a positive temperature coefficient d. Is an active load

ANSWERS: 1. c. E-MOSFET 2. c. Threshold voltage 3. d. All of the above 4. d. Greater than VGS(th) 5. c. A passive load 6. b. An active load 7. d. A switching device 8. d. Complementary MOS 9. c. Greater than VGS(th) 10. a. Two-terminal device 11. b. Complementary E-MOSFETs 12. d. Low power consumption 13. d. Used to switch large currents 14. c. Drain current decreases 15. d. Integrated circuits 16. a. Used in high-current applications 17. b. An N-Type inversion layer 18. d. Complementary 19. d. VDD

20. c. Has a positive temperature coefficient