ELC224 Final Review (12/10/2009) Name: Select the correct answer to the problems 1 through 20. 1. A common-emitter amplifier that uses direct coupling is an example of a dc amplifier. 2. The frequency response of an ac amplifier shows increased voltage gain at low frequencies because of the effects of capacitive reactances. 3. The frequencies at which the voltage gain equals 1.414 of its maximum value are called the halfpower frequencies. 4. A designer can use capacitive coupling between amplifier stages in order to amplify down to 0 Hz. 5. Each time the ordinary power gain decreases by a factor of 2, the decibel power gain decreases by 10 db. 6. The term differential amplifier refers to an amplifier that performs a mathematical operation. 7. A diff amp is sometimes called a long-tail pair because the two transistors share a common emitter resistor. 8. Base resistors can produce input error voltages when the two halves of the diff amp are perfectly symmetrical. 9. The input impedance of a diff amp is twice as high as a single common-emitter amplifier. 10. Most op amps available today are high-power devices with a maximum power rating of more than a watt.
11. The Miller effect has useful applications because A. it creates virtual capacitors that are much larger than the feedback capacitor B. it creates virtual resistors that are much larger than the load resistor C. it creates additional gain without adding amplifiers D. it makes coupling capacitors appear smaller than they actually are 12. What type of circuit rolls off voltage gain and prevents an op amp from oscillating? A. Attenuator B. RC lead C. RC lag D. LC lag 13. What is the fastest and most accurate way to analyze the frequency response of a discrete BJT or FET amplifier? A. use MultiSim or other circuit simulation software B. use square wave testing C. use sine wave injection and oscilloscope signal tracing D. use frequency generator injection and frequency counter testing 14. When two or more monolithic ICs are fabricated in one package, they are referred to as A. hybrid B. thoroughbred C. discrete D. compensated 15. In order to get single-ended operation when using a diff amp A. one input is used and the other is grounded B. one input is connected to the power supply and the other is grounded C. both inputs are used D. both inputs are grounded 16. When a differential amplifier is not perfectly symmetrical A. there will be a small ac output voltage B. there will be no common-mode amplification C. there will be no ac output voltage D. there will be 0 V at the output 17. Ultra large scale integration refers to placing approximately how many components on a single chip? A. 12 to 100 B. more than 100 C. thousands D. more than a million 18. What is the op amp circuit used when it is necessary to combine two or more analog signals into a single output? A. voltage follower B. comparator C. summing amp D. diff amp
19. Which op amp is the least expensive and most widely used? A. 741A B. 741N C. 741E D. 741C 20. The best method to eliminate output error and minimize thermal drift of an op amp is by A. connecting a compensating capacitor B. using a nulling circuit C. using a tuned amplifier D. using a RLC filter Fill in the blank for the problems 16-25. 21. A op amp circuit uses feedback to stabilize the overall gain, increase the input impedance, and decrease the output impedance. 22. Op amps designed with minimum imperfections and intended for applications such as measurement and control are referred to as op amps. 23. Because of the heavy negative feedback, the current-controlled current source tends to act like a perfect amplifier. 24. The conversion factor of the current-controlled voltage source is called. 25. The worst-case error of closed-loop voltage gain occurs when the open-loop voltage gain is.
Use Figure 1 to answer problems 26 through 29. Show all your works. 26. Determine the resonant frequency f s. 27. Determine the quality Q s. 28. Determine the bandwidth BW. 29. Sketch the curve of A vdb versus frequency using the idealized Bode plots as an envelope for the actual response.
Use Figure 2 to answer problems 30 through 34. Show all your works. All capacitors are 20 µf. Show all your works. Given CC = 2 pf, Ce = 10 pf, and Cstray = 5 pf. 30. What is the low-cutoff frequency for the base coupling circuit? 31. What is the low-cutoff frequency for the collector coupling circuit? 32. What is the low-cutoff frequency for the emitter bypass circuit? 33. Determine the high-cutoff frequency base-input circuit. 34. Determine the high-cutoff frequency collector-output circuit.
Use Figure 3 to answer problems 35 and 39. Show all your works. 35. What is the DC tail current? Use the second approximation. 36. What is the DC emitter current? 37. What is the DC output voltage? 38. What is the AC output voltage? 39. If β = 300, what is the input impedance of the diff amp?
Use Figure 4 to answer problems 40 through 44. Show all your works. 40. The 741C op amp circuit has a load resistance of 10 kω. How much inverting input voltage does it take to drive the 741C into negative saturation? 41. What is the common-mode rejection ratio CMRR of the 741C when the input frequency is 100 khz? 42. What is the open-loop voltage gain of the 741C when the input frequency is 100 khz? 43. The input voltage to an op amp is a large voltage step. The output is an exponential waveform that changes to 0.25 V in 0.1 µs. What is the slew rate of the op amp? 44. The LF411A has a slew rate of 15V/µs. What is the power bandwidth for a peak output voltage of 10V?
Use Figure 5 to answer problems 45 through 50. Show all your works. The 741C has a typical A VOL of 100,000, the open-loop input resistance R in of 2 MΩ, the common-mode input resistance R CM of 200 MΩ, the open-loop output resistance R out of 75 Ω, and the unity-gain frequency f unity of 1 MHz. 45. What is the feedback fraction B? 46. What is the ideal closed-loop voltage gain A v? 47. What is the ideal closed-loop voltage gain A v? 48. What is the closed-loop input impedance z in(cl)? 49. What is the closed-loop output impedance z out(cl)? 50. What is the closed-loop bandwidth f 2(CL)?