School of Sciences SPRING SEMESTER 2010 INSTRUCTOR: Dr Konstantinos Katzis COURSE / SECTION: ECE212N COURSE TITLE: Electronics II OFFICE RM#: 124 (1 st floor) OFFICE TEL#: 22713296 OFFICE HOURS: Monday (15:00 18:00), Wednesday (10:30 11:30), Thursday (9:30 11:30) EMAIL: : K.Katzis@euc.ac.cy Website : http://faculty.euc.ac.cy/kkatzis/ ELECTRONICS II ECE212A 2 nd Assignment Answer 20 questions out of the 29 Deadline 12 th April 2010 1
Exercise 1 Figure 1, includes a variable resistor of 1kΩ. If this is adjusted to 780Ω, what is the voltage gain? 1 15 g m =2000μS 1MΩ 1k 3k 200Ω Figure 1 Exercise 2 A JFET shunt switch has R D =10kΩ, I DSS =10mA, and V GS (off)=2v. If V in =10mV(peakpeak) what are output voltages? What is the onoff ratio? Exercise 3 What is the drain voltage for figure 2? Draw the DC load line and Q point for figure 2. 1.5MΩ 10KΩ 1 1MΩ 22K Figure 2 2
Exercise 4 Calculate R DS(on) for each of these EMOSFET values: a. V DS(on) = 0.1V and I D(on) = 10 ma b. V DS(on) = 0.25V and I D(on) = 45 ma c. V DS(on) = 0.75V and I D(on) = 100 ma d. V DS(on) = 0.15V and I D(on) = 200 ma Exercise 5 An EMOSFET has R DS(on) = 2Ω when V GS(on) =3V and I DS(on) =500mA. If it is biased in the ohmic region, what is the voltage across it for each of these drain currents: a. I DS(sat) =25mA b. I DS(sat) =50mA c. I DS(sat) =100mA d. I DS(sat) =200mA Exercise 6 What is the output voltage in figure 3a and 3b when the input is low and when the input is high? Comment (compare) the switching performance of the two circuits. 10V 20V R D =2kΩ R D =10kΩ Vout Vout Vin R D =500Ω Vin R D =50Ω Figure 3a. Figure 3b. Exercise 7 An amplifier has a midband voltage gain of 1000. If cutoff frequencies are f 1 =100Hz and f 2 =100kHz, what does the frequency response look like? What is the voltage gain if the input frequency is 20Hz? If it is 300Hz? Exercise 8 A two stage amplifier has these stage gains: A 1 =25.8 and A 2 =117. What is the decibel voltage gain of each stage? What is the total voltage gain? 3
Exercise 9 The data sheet of an opamp gives a midband voltage gain of 200,000, a cut off frequency of 10Hz and a roll off rate of 20dB per decade. Draw the ideal bode plot. What is the ordinary voltage gain at 1MHz? Exercise 10 If the feedback capacitor in figure 4 is 50pF, what is the Miller capacitance when A=200,000? Draw the ideal Bode plot for the input lag circuit of figure 4 with A=250,00 and C=15pF. C 1kΩ A 10kΩ Figure 4 Exercise 11 In figure 5, what is the ac output voltage? If β=300, what is the input impedance of the diff amp? 15V 6kΩ 6kΩ 1mV 7.5kΩ 15V Figure 5 Exercise 12 Explain the concept of current mirror and why it is used. 4
Exercise 13 Calculate the ideal currents and voltages in figure 6? Calculate the currents and voltages in figure 6 using the 2nd approximation. 12V 180kΩ 180kΩ 270kΩ 12V Figure 6 Exercise 14 In figure 7, that is the ac output voltage? If β=275, what is the input impedance of the diff amplifier? Use the ideal approximation to get the tail current. 20V 47kΩ 47kΩ 2.5mV 68kΩ 20V Figure 7 Calculate the tail current using the 2 nd approximation. 5
Exercise 15 a) What is an ideal op amp? Compare the properties of a to those of an ideal op amp. b) Draw an op amp with an input voltage step. What is slew rate and why is it important? c) Draw an inverting amplifier using an op amp with component values. Identify the virtual ground. What are the properties of the virtual ground? What are the closed loop voltage gain, input impedance and bandwidth? d) Draw a noninverting amplifier using an op amp with component values. Identify the virtual short. What are the properties of the virtual short? What are the closed loop voltage gain, input impedance and bandwidth? Exercise 16 Draw a summing amplifier and explain me the theory of operation. Exercise 17 What are the closedloop voltage gain and bandwidth in figure 8 when f unity is 20 MHz? What is the output voltage at 1kHz and 2MHz? Draw the ideal Bode plot of closed loop voltage gain. 3kΩ 25mV 150Ω LF157A Figure 8 Exercise 18 In figure 9, what are the closedloop voltage gain and bandwidth? The ac output voltage at 100kHz? 15V 25mV LF157A 3kΩ 15V 150Ω Figure 9 6
What is the output voltage when V in is reduced to zero? (Assume worst case parameters: I in(bias) = 50pA, I in(off) =10pA, and V in(off) =2mV). Exercise 19 What is the output voltage of the circuit in figure 10 if the input frequency is 1kHz? 5kΩ 15V 1mApp 15V 200Ω Figure 10 What are the closedloop input and output impedances in figure 10 (Use A v =100,000) Exercise 20 In figure 11, calculate the feedback fraction and the ideal closed loop voltage gain. (A OL_dB =88dB) 12V 20mV LF351 68kΩ 12V 2.7kΩ Figure 11 If the 68kΩ resistor of figure 11 is changed to 39kΩ, what is the feedback fraction? The closed loop voltage gain? 7
Exercise 21 Suppose the amplifier of figure 12 has an open look total harmonic distortion of 10%. What is the closed loop total harmonic distortion? AOL=200,000 9V 2mVpp 7.5kΩ 9V 100Ω Figure 12 Exercise 22 What is the total current in figure 13? The load power? What happens if the load resistance changes to 4Ω? 15V 2Vrms LM12 15V 2Ω i out 1Ω Figure 13 Exercise 23 The differential amplifier of figure 14 has R1=1.5kΩ and R2 = 30kΩ. What is the differential voltage fain? The commonmode gain? (Resistor tolerance = / 1%) 8
V in(cm) R 1 R 2 15V V in(cm) V in R 1 R 2 15V Figure 14 Exercise 24 Draw the schematic diagram of a differential amplifier build with an opamp. What are the factors that determine the CMRR? Exercise 25 If R 1 =10MΩ, R 2 =20MΩ, R 3 =15kΩ, R 4 =15kΩ and R 5 =75kΩ of figure 15, calculate the gain for switch position A and B. R 1 R 2 A R 4 V in R 3 B R 5 Figure 15 Exercise 26 In the accoupled inverting amplifier of figure 16, R 1 =1.5kΩ, R 2 =82kΩ, R L =15kΩ, C 1 =1μF, C 2 =4.7μF, and f unity = 1MHz. What is the voltage gain in the midband of the amplifier? What are the upper and lower cutoff frequencies? 9
C 1 R 1 R 2 V in C 2 R L Figure 16 Exercise 27 In the Wheatstone bridge of figure 17, R 1 =10kΩ, R 2 =20kΩ, R 3 =20kΩ, R 4 =10kΩ. Is the bridge balanced? Vcc R 1 R 3 R 2 R 4 Figure 17 Exercise 28 In the summing circuit of figure 18, R 1 =10kΩ, R 2 =20kΩ, R 3 =15kΩ, R 4 =15kΩ, R 5 =30kΩ, R F =75kΩ. What is the output voltage if v 1 =1mV, v 2 =2mV, v 3 =3mV, v 4 =4mV. 10
R 1 R F V 1 V 2 R 2 R 3 R 5 V 3 R 4 V 4 Figure 18 Exercise 29 What are the pole frequency and Q of the filter shown in figure 19? What is the cutoff frequency? 330pF V in 47kΩ 47kΩ 330pF 30kΩ 51kΩ Figure 19 11