2025 Fall BiS350 Bioengineering Lab II Lab 2 - 1 © 바이오및뇌공학과 2025 Lab 2. Operational Amplifier Circuits 1. Objective To understand configurations of operational amplifier circuits. 2. Theoretical Background Operational amplifier is the most commonly used analog IC(integrated circuit). The following list describes the concepts to be covered in this lab: 1. Working principle of OP amp 2. Inverting/non-inverting amplifiers 3. Superposition 4. Adder/subtractor circuits 5. Instrumentation amplifier Please read Operational Amplifiers and Linear Integrated Circuits 6th edition (Supplementary material 1) by Robert F. Coughlin and Frederick F. Friscoll, and LM741 datasheet (Supplementary material 2), to acquire basic knowledge about the experiment. 3. Pre-Lab Activities In this lab, students will implement various functional circuits using operational amplifier LM741. Students should use the proper instrumental device in order to generate/receive signals. (1) LM 741 1. There are many electronic parameters listed on LM 741 datasheet (e.g., Input offset voltage, adjustment range, supply current...). Choose 6 parameters and briefly explain each, what it means and why it is important. 2. There are 8 pins in LM 741. Briefly describe the role of each. Fig. 1 LM 741 2025 Fall BiS350 Bioengineering Lab II Lab 2 - 2 © 바이오및뇌공학과 2025 (2) Voltage-level detector Figure 2(a) shows an example of electrocardiogram (ECG) signal of a patient. The pulse rate can be calculated by counting the number of “peaks” that occur in one minute. To detect the peaks and calculate the pulse rate, the circuit should have certain threshold (Vx), which can be implemented as a step function as shown in Figure 2(b). Fig. 2 Voltage level detector 1. Graphically represent the expected output signal on (c) with proper x, y-axis. Explain how voltage-level detector can detect R-R interval. 2. Design a voltage detector that can achieve Fig.2 (b). (Hint: refer supplementary material 1) * You must clarify the value of voltage that you applied. (i.e. +V = 20V and etc.) (3) Inverting and non-inverting amplifiers Fig. 3 Inverting and Non-Inverting Amplifiers 2025 Fall BiS350 Bioengineering Lab II Lab 2 - 3 © 바이오및뇌공학과 2025 1. What is the difference between inverting and non-inverting amplifier? Show this in the circuit diagram and voltage equation. You should derive the all equations with your own calculation using R1, RL, Rf and Ei. 2. Draw a pinout diagram of the LM 741, and redraw the circuit diagram in Figure 3 over the pinout diagram. This will be helpful for your main lab activity. * You must clarify the value of voltage that you applied. (i.e. +V = 20V and etc.) 3. If Ei in Fig. 3(b) was given to the circuit as an input, what would the output voltage look like? (4) The adder/subtractor circuit below implements the function of ‘Y=mX+b’. Fig. 4. Linear Equation Amplifier 1. Derive an equation that expresses the result of V out in Fig. 4. 2. Draw a pinout diagram of the LM 741, and redraw the circuit diagram in Figure 4 over the pinout diagram. * You must clarify the value of voltage that you applied. (i.e. +V = 20V and etc.) 3. What should be done to remove the y-intercept in the formula? (5) Instrumentation amplifier Fig. 5 Instrumentation amplifier 2025 Fall BiS350 Bioengineering Lab II Lab 2 - 4 © 바이오및뇌공학과 2025 1. Describe the advantages and disadvantages of an instrumentation amplifier and its uses. 2. Derive an equation for V out 3. Again, draw the pinout diagram of LM 741 (in this case, three op-amps will be used), and redraw the circuit diagram in Figure 5 over it. 4. Main-Lab Activities 4.1. After this lab, students will be able to... i. Read a datasheet of various electronic devices, i. g., Op-Amp 741. ii. Try out a voltage-level detector iii. Build an inverting/non-inverting amplifier iv. Build an adder/subtractor circuit v. Build a basic instrumentation amplifier 4.2. Required Materials A. Lab Equipment i. Oscilloscope ii. Digital multimeter iii. Power supply iv. Function generator v. Breadboard B. Circuit Components i. Resistors ii. Op-Amp 4.3. Procedure 1. Implement a voltage-level detector. (Refer supplementary 1 in p. 22, Fig. 2-5) 2. Implement an inverting, and a non-inverting amplifier. (Refer supplementary 1, p. 48 and 58, Fig 3-2 and 3-7 respectively.) 3. Implement an adder, and a subtractor circuit. (Refer supplementary 1, p.72.) a. Create a circuit that implements the function ‘y= -4x-3’. Refer to Fig. 3-17. b. Enter a 2V sine wave into Ei, and 2V DC into Edc. Note down the result. 4. Implement a basic instrumentation amplifier. (Refer supplementary 1, p.226, Fig. 8-6) a. Enter 3Vdc into E1 and 1Vdc into E2 in a way that would cause 8Vdc output voltage. b. Input a 10Hz 3Vp.p triangle wave into E1, and a 20Hz 1Vp.p sine wave into E2. 2025 Fall BiS350 Bioengineering Lab II Lab 2 - 5 © 바이오및뇌공학과 2025 4.4. Discussion 1. In Fig.3, it shows inverting and non-inverting amplifier. To make the circuit implement the function ‘y=4x+3’, how do you need to change? 2. When you put a high frequency signal to the input of instrumentation amplifier, you can observe the gain is decreased. What is the reason? 5. Conclusion 1. Write a final report summing up the results from the main-lab experiment. You can freely include additional discussions about results in your report. (Add essential 2 discussions that will be announced at “Main Lab”.) 6. References [1] 김충기 , 김형명 , 박철훈 , 전자공학 기초실험 , 대영사 , 2001 [2] A.S.Sedra, K.C.Smith, Microelectronic Circuits 4 th Ed. Oxford, 1998, pp.86-88 [3] Robert F. Coughlin, Frederick F. Friscoll, “Operational Amplifiers and Linear Integrated Circuits” 6 th edition, page 13-117 [4] LM741 datasheet.