Experiment 7 Report

pdf

School

University of California, Los Angeles *

*We aren’t endorsed by this school

Course

110L

Subject

Electrical Engineering

Date

Apr 3, 2024

Type

pdf

Pages

Uploaded by DrProtonRhinoceros39

ECE 110L Winter 24’ Instructor: Mesghali, Farid Exp. 7: Operational Amplifiers Om Patel, 605518179 Experiment Introduction and Theory In this set of labs, we explored basic amplifier structures using operational amplifiers in negative-positive feedback. An op amp is a voltage-controlled voltage source with a very high gain. It works off of a very large input impedance and very small output impedance. Out of the 8 pins, 2 of them are power pins which should always be connected to the power supply. Another 2 are input pins and 1 other is an output pin which will output the amplified voltage difference between the terminal pins. The last 3 pins are the no connect pins which can be ignored for these labs. In the first part of this experiment, we will dive into negative feedback for op-amps. Negative feedback is when there is a path formed between the output and the negative input. For an inverting amplifier, the negative of the input signal is amplified. This is shown in Figure 1. For a non-inverting amplifier, the input signal is amplified. This is shown in Figure 2. For the last part, we will be exploring the positive feedback of an op-amp which causes a large positive output voltage from a small positive input voltage. Positive feedback circuits are naturally very unstable because a change in the input drastically changes the output. This is shown in Figure 3. 𝑉 ??? 𝑉 𝑖? =− 𝑅 𝑓 𝑅 1 Figure 1: Inverting Amplifier with negative feedback 𝑉 ??? 𝑉 𝑖? = 1 + 𝑅 𝑓 𝑅 1 Figure 2: Non-inverting Amplifier with negative feedback 𝑉 ??? 𝑉 𝑖? = 𝑅 2 𝑅 1 (? 𝑖?2 − ? 𝑖?1 ) Figure 3: Differential amplifier based on inverting/non-inverting amplifiers

𝑇 = 2𝑅 1 𝐶𝑙?( 𝑅 2 +2𝑅 3 𝑅 2 ) Figure 4: Positive Feedback op-amp circuit Lab 1: Unity gain buffer design Introduction: In this part of the lab, a unity gain buffer design was studied. After constructing the circuit shown below, the voltage across the inductor was measured through the AD-2. We used the OPA705 op-amp with a voltage supply of 1V at 1kHz. Figure 5: Voltage divider circuit diagram for Lab 1 Figure 6: Voltage divider constructed circuit for Lab 1 Figure 7: Unity gain buffer circuit diagram for Lab 1 Figure 8: Unity gain buffer constructed circuit for Lab 1

Measured Data: Component Measured Value Theoretical Value Resistor 1(Ω) 986 1000 Resistor 2(Ω) 989 1000 V L without unity gain (V) 0.5 V L with unity gain (V) 1 Table 1: Lab 1 Data Discussion: 1. The circuits have different transfer functions because they contain different circuit elements. 2. One includes just two resistors while the other includes an op-amp. With the latter circuit, the voltage into the input terminals stays constant and no current is flowing. While with the first one, the resistors eat up voltage and make it so the output voltage is not the same as the voltage source.

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

Lab 2: Inverting and non-inverting gain amplifier design Introduction: In this part of the experiment, the inverting/non-inverting gain amplifier was explored. After constructing the circuit shown below using 5 100 ohm resistors and the OPA705 op-amp, the output voltage was measured using the AD-2. For Vin1 a voltage supply of 1V at 100Hz was used while for Vin2 the magnitude was the same but just negative. 𝑉 ??? 𝑉 𝑖? = 𝑅 2 𝑅 1 (? 𝑖?2 − ? 𝑖?1 ) Figure 3: Differential amplifier based on inverting/non-inverting amplifiers Figure 11: Differential amplifier with Vin2 grounded Figure 12: Differential amplifier with Vin1 grounded Figure 13: Differential amplifier with no sources grounded Figure 14: Differential amplifier with Vin1=-Vin2

Measured Data: Component Measured Value Theoretical Value Resistor 1(Ω) 986 1000 Resistor 2(Ω) 989 1000 Resistor 3(Ω) 985 1000 Resistor 4(Ω) 987 1000 Resistor 5(Ω) 987 1000 Resistor 6(Ω) 986 1000 Table 2: Measured and theoretical values for circuit elements/analyzed variables Measured Theoretical Part A V_in,1 1 1 V_in,2 0 0 V_o -1.0021 -1.0030 V_o/V_in -1.0021 -1.0030 Part B V_in,1 0 0 V_in,2 0.9986 1 V_o 0.9644 1.0025 V_o/V_in 0.9657520529 1.0025 Part C V_in,1 1 1 V_in,2 1 1 V_o -0.05277 -0.0005 V_o/V_in -0.05277 -0.0005 Part D V_in,1 -0.99946 -1 V_in,2 0.99946 1 V_o 2 2.006 V_o/V_in 2.001080584 2.006 Part E CMRR -25.5523 -17 to -30db Table 3: Lab 2 Data

Figure 15: Voltage output for Vin2 grounded Figure 16: Voltage output for Vin1 grounded Figure 17: Voltage output with no source grounded Figure 18: Voltage output with Vin1=-Vin2 Discussion: 1. a. 𝑉 ??? =− 𝑅 2 𝑅 1 𝑉 𝑖?1 b. 𝑉 ??? = 𝑅 4 𝑅 3 +𝑅 4 (1 + 𝑅 2 𝑅 1 )𝑉 𝑖?2 2. a. 𝑉 ??? =− 𝑅 2 𝑅 1 𝑉 𝑖?1 + 𝑅 4 𝑅 3 +𝑅 4 (1 + 𝑅 2 𝑅 1 )𝑉 𝑖?2 b. 𝑉 ??? = 𝑅 2 𝑅 1 (𝑉 𝑖?2 − 𝑉 𝑖?1 ) 3. Common mode rejection ratio = -25.55 dB

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

Lab 3: Positive feedback and Oscillator Introduction: In this part of the experiment, we explored positive feedback using the oscilloscope. The AD-2 was used as a power source for the op-amp and then the frequency was found from the oscilloscope. 𝑇 = 2𝑅 1 𝐶𝑙?( 𝑅 2 +2𝑅 3 𝑅 2 ) Figure 4: Positive Feedback op-amp circuit Figure 19: Positive Feedback constructed op-amp circuit Measured Data: Component Measured Value Theoretical Value Resistor 1(Ω) 98600 100000 Resistor 2(Ω) 983 1000 Resistor 3(Ω) 9950 10000 Capacitor 1(nF) 10.17 10 Table 4: Measured and theoretical values for circuit elements/analyzed variables Measured Value Theoretical Value T VP (secs) 0.006569 0.006129 T vn (secs) 0.006764 0.006129 fos vp (Hz) 152.22 163.16 fos vn (Hz) 147.82 163.16 Table 5: Lab 3 Data

Figure 20: Oscilloscope reading #1 Figure 21: Oscilloscope reading #2 Discussion: 1. No discussion questions were presented.

Signature of Professor: Prelab: Lab 1: - Find V 0 /V s for both circuits in Fig. 6 Lab 2: For V in =1V, 1kHz - Find V 0 /V in1 and V 0 , when V in2 = 0 - Find V 0 /V in2 and V 0 , when V in1 = 0 - Find V 0 , when V in1 =V in2 - Find V 0 , when V in1 =-V in2 Lab 3: - Find the period and frequency of the oscillation for the circuit in Fig. 9.

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version