ECE225L Lab: Experiment 7 - Op-Amps in Circuit Analysis & Design at Boise State, Lab Reports of Electrical Circuit Analysis

Download ECE225L Lab: Experiment 7 - Op-Amps in Circuit Analysis & Design at Boise State and more Lab Reports Electrical Circuit Analysis in PDF only on Docsity! Boise State University Department of Electrical and Computer Engineering ECE225L – Circuit Analysis and Design Lab Experiment #7: Basics of Operational Amplifiers 1 Objectives The objectives of this laboratory experiment are: • To demonstrate the operation of a 741 op-amp by investigating common configurations such as the inverting amplifier, non-inverting amplifier, summing amplifier, and difference amplifier. 2 Theory An operational amplifier (op-amp for short) is a voltage amplifier with a very high voltage gain. An op-amp has two inputs: an inverting input, Vn, and a non-inverting input, Vp. When used in an open-loop configuration, the output voltage is governed by the relationship: Vo = A(Vp − Vn) (1) where A is the open-loop gain which is typically 104-105. This gain varies widely from one op-amp to another and thus the op-amp is rarely used in an open-loop configuration. This gain can be reduced by using negative feedback. This involves connecting the output of the op-amp to the inverting input through a “feedback network,” usually composed of resistors. This will reduce the overall gain of the op-amp. A major advantage of this feedback loop is that the new gain can be controlled precisely and is practically independent of A which can vary from device to device. 6 7 81 − + NC NC NC +V CC −V CC V n V V op 5 2 3 4 Figure 1: LM741N Op-Amp (Top View) Figure 1 shows the pin configuration of 741 op-amp. This type of op-amp is an integrated circuit (IC) in a mini-DIP (Dual In-Line Package). The five relevant pins are shown in Figure 1. Vn and Vp are the inverting and non-inverting inputs, respectively, while Vo is the output. +VCC is the positive power supply and −VCC is the negative power supply. These two supply voltages limit the output voltage range so that −VCC ≤ Vo ≤ + VCC (2) 1 and the output voltage “saturates” at ±VCC . 2 R 1 R i v − + o v − + + − 6 3 2 Figure 2: Inverting Op-Amp Configuration Figure 2 shows an inverting op-amp circuit. In this case, a feedback resistor, R2, is connected to the inverting input. With feedback, the ideal closed-loop voltage gain assuming an infinite op-amp gain A is given by vo vi = −R2 R1 (3) 2 3 1 R 2 R i v o v −− + + − + 6 Figure 3: Non-Inverting Op-Amp Configuration Figure 3 shows a non-inverting op-amp circuit. The input resistance for this circuit is greater than 10 MΩ. The ideal gain for this circuit is given by vo vi = R1 + R2 R1 = 1 + R2 R1 (4) Note that the polarity of the ouput is the same as that of the input while the output polarity of the inverting amplifier is opposite that of the input. Also, note that both Figure 2 and Figure 3 show feedback to the inverting input. 2 4 Procedure 100k 10k −15 V +15 V i v − + o v − + + − 6 3 2 Figure 6: Inverting Op-Amp Test Circuit 1. Measure and record the values of a 10k and 100k resistors using your handheld multimeter set on ohms. R1 (Ω) R2 (Ω) Nominal 10k 100k Measured 2. Wire the circuit shown in Figure 6 on your protoboard. 3. For each of the DC input voltages, measure and record the input and output voltages using your handheld multimeter set on DC voltage. vi (VDC) vo (VDC) G = vo/vi 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 4. Measure and record the values of a 1k and 9.1k resistors using your handheld multimeter set on ohms. R1 (Ω) R2 (Ω) Nominal 1k 9.1k Measured 5 −15 V +15 V 1k 9.1k i v o v −− + + − + 6 Figure 7: Non-Inverting Op-Amp Test Circuit 5. Wire the circuit shown in Figure 7 on your protoboard. 6. For each of the DC input voltages, measure and record the input and output voltages using your handheld multimeter set on DC voltage. vi (VDC) vo (VDC) G = vo/vi 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 5 Report Questions 1. Plot the output voltage as a function of the input voltage using the measurements from the circuit in Figure 6. Comment on the shape of the resulting curve. Compute the slope of the linear portion and compare it to the ideal gain using Equation (3) and the measured resistance values. 2. Plot the output voltage as a function of the input voltage using the measurements from the circuit in Figure 7. Comment on the shape of the resulting curve. Compute the slope of the linear portion and compare it to the ideal gain using Equation (4) and the measured resistance values. 6 Boise State University Department of Electrical and Computer Engineering ECE225L – Circuit Analysis and Design Lab Experiment #7: Basics of Operational Amplifiers Date: Data Sheet Recorded by: Equipment List Equipment Description BSU Tag Number or Serial Number Fluke 111 True RMS Multimeter HP/Agilent E3631A Triple Output Power Supply Part 1: Inverting Op-Amp Configuration: vi (VDC) vo (VDC) G = vo/vi 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 R1 (Ω) R2 (Ω) Nominal 10k 100k Measured Part 2: Non-Inverting Op-Amp Configuration: vi (VDC) vo (VDC) G = vo/vi 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 R1 (Ω) R2 (Ω) Nominal 1k 9.1k Measured