Lecture Notes Unit-III

Transcription

1 Lecture Notes Unit-III

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31 FAQs Q1: An operational amplifier has a differential gain of 103 and CMRR of 100, input voltages are 120µV and 80µV, determine output voltage. 2 MARKS [ ] Q2: List the ideal characteristics of Op-Amp. 2 MARKS [ ] Q3: Explain the following: 10 MARKS [ ] a) Voltage Follower b) Non inverting amplifier c) Differential amplifier in two modes of operation Q4: Find output voltage of the Op-Amp. V 1 =0.1V, V 2 =0.2V, V 3 =0.3V, R 1 =20 KΩ, R 2 =10 KΩ, R 3 =50 KΩ. 5 MARKS [ ] Q5: Find output voltage of the op-amp. R 1 = 5 KΩ, R 2 = 10 KΩ, R 3 = 5 KΩ, R 4 = 5 KΩ 5 MARKS [ ] Q6: Define Op-Amp and draw its block diagram. 5 MARKS [ ] Q7: Draw the equivalent circuit of Op-Amp with its ideal and practical characteristics. 5 MARKS [ ] Q8: Analyze the differential amplifier with suitable circuit in two modes of operation. 5 MARKS [ ] Q9: Determine the output voltage of an Op-Amp for input voltages of 200 V and 140 V. The amplifier has a NIET Greater Noida ECE Department Electronics Engineering Confidential

32 differential gain of 6000 and the value of CMRR is MARKS [ ] Q10: For an input of 50 mv, determine the maximum frequency that may be used for the Op-Amp in non- inverting configuration if its slew rate is 0.4 μv/s. 5 MARKS [ ] Q11: Define CMRR, and slew rate of an Op-Amp. 2 MARKS [ ] Q12: Show that how input voltage gets reversed using operational amplifier. Also derive the expression for voltage gain using inverting amplifier. 5 MARKS [ ] Q13: Explain with the necessary diagram of inverting and non-inverting amplifier. 5 MARKS [ ] Q14: Draw the circuit of an Op-Amp as voltage follower and find an expression for its voltage gain. 5 MARKS [ ] Q15: Explain with the necessary diagram an integrator circuit using Op-Amp. 5 MARKS [ ] Q16: Explain Differentiator circuit using Op-Amp. 5 MARKS [ ] Q17: Find out the voltage V 2 and V 3 of the network of the figure. 10 MARKS [ ] NIET Greater Noida ECE Department Electronics Engineering Confidential

33 SUGGESTED ANSWER OF FAQs Q1: An operational amplifier has a differential gain of 103 and CMRR of 100, input voltages are 120µV and 80µV, determine output voltage. 2 MARKS [ ] Sol. Use V 0 = A d V d + A c V d, CMRR = A d /A c, V o = 4.2 mv. Q2: List the ideal characteristics of Op-Amp. 2 MARKS [ ] Sol. Parameters Ideal values Practical values Open Loop Voltage Gain 20,0000 Input Impedance 2 MΩ Output Impedance Input offset voltage Input offset current Input bias current Ω 2 mv 20 na 80 na Bandwidth 1 MHz CMRR 90dB Slew Rate 0.5 V/μ-sec Q3: Explain the following: 10 MARKS [ ] d) Voltage Follower e) Non inverting amplifier f) Differential amplifier in two modes of operation NIET Greater Noida ECE Department Electronics Engineering Confidential

34 Sol: a) Voltage Follower The Voltage Gain is unity Highest Bandwidth High input impedance Low output impedance Impedance Matching Reduced output offset voltage b) Non Inverting amplifier c) Differential amplifier in two modes of operation NIET Greater Noida ECE Department Electronics Engineering Confidential

35 Differential Mode Common Mode Q4: Find output voltage of the Op-Amp. V 1 =0.1V, V 2 =0.2V, V 3 =0.3V, R 1 =20 KΩ, R 2 =10 KΩ, R 3 =50 KΩ 5 MARKS [ ] Sol : Apply : NIET Greater Noida ECE Department Electronics Engineering Confidential

36 Q5: Find output voltage of the op-amp. R 1 = 5 KΩ, R 2 = 10 KΩ, R 3 = 5 KΩ, R 4 = 5 KΩ 5 MARKS [ ] Sol : Apply Nodal at both the input terminals and using virtual short concept get : V o = (V 2 R 4 )/(R 3 +R 4 ) - (V 1 R 2 )/(R 1 +R 2 ) Q6: Define Op-Amp and draw its block diagram. 5 MARKS [ ] Sol : It is defined as a high gain differential amplifier with a high input impedance (typically in M ) and low output impedance (less than 100 ). It performs different types of Mathematical Operations. Block Diagram of Op-Amp : Q7: Draw the equivalent circuit of Op-Amp with its ideal and practical characteristics. 5 MARKS [ ] Sol: Equivalent circuit for ideal and practical characteristics refer to question no 2. Q8: Analyze the differential amplifier with suitable circuit in two modes of operation. 5 MARKS [ ] NIET Greater Noida ECE Department Electronics Engineering Confidential

37 Sol : Refer to question no 3(c). Q9: Determine the output voltage of an Op-Amp for input voltages of 200 μv and 140 μv. The amplifier has a differential gain of 6000 and the value of CMRR is MARKS [ ] Sol: Use V 0 = A d V d + A c V d, CMRR = A d /A c, V o = 6000* *170 = = mv Q10: For an input of 50 mv, determine the maximum frequency that may be used for the Op-Amp in noninverting configuration if its slew rate is 0.4 μv/s. 5 MARKS [ ] Sol : V 0 = 1.2 volts w max = SR/V 0 = 3.33*10 5 rad/sec. Q11: Define CMRR, and slew rate of an Op-Amp. 2 MARKS [ ] Sol: CMRR is the ability of a Differential Amplifier (Op-Amp) to reject the common mode signals successfully and defined as the ratio of Differential mode gain and Common mode gain. CMRR = A d /A c. Slew rate is the maximum rate at which an Op-Amp can change output without distortion and expressed in Volt per microsecond. Q12: Show that how input voltage gets reversed using operational amplifier. Also derive the expression for Sol: voltage gain using inverting amplifier. 5 MARKS [ ] NIET Greater Noida ECE Department Electronics Engineering Confidential

38 Q13: Explain with the necessary diagram of inverting and non-inverting amplifier. 5 MARKS [ ] Sol : Refer to question no. 3 and 12. Q14: Draw the circuit of an Op-Amp as voltage follower and find an expression for its voltage gain. 5 MARKS [ ] Sol : NIET Greater Noida ECE Department Electronics Engineering Confidential

39 Q15: Explain with the necessary diagram an integrator circuit using Op-Amp. 5 MARKS [ ] Sol: NIET Greater Noida ECE Department Electronics Engineering Confidential

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41 Q16: Explain Differentiator circuit using Op-Amp. 5 MARKS [ ] Sol : NIET Greater Noida ECE Department Electronics Engineering Confidential

42 Q17: Find out the voltage V 2 and V 3 of the network of the figure. 10 MARKS [ ] NIET Greater Noida ECE Department Electronics Engineering Confidential

43 Sol : V 2 = -(200/20)*0.2 = 2volts V 3 = [1+(200/20)]*0.2 = 2.2volts NIET Greater Noida ECE Department Electronics Engineering Confidential