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ECE20B Lab, Winter 2002
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Lab 1 Prelab Assignment (Week 2, January 14 - 18)
Reading Assignment:
Lab Book (Carley and Khosla) Chapter 7 (Operational Amplifiers)
Reference: ECE 20B Lectures, Rizzoni, pgs 541-552
Prelab Questions:
1. (1 point) Label the input, output and bias (power supply) ports of an op-amp,
give the equation governing the Vout in terms of the other voltages. Briefly
describe this equation.
2. (1 point) Describe the operation of the comparator circuit shown in Fig. 2.1;
calculate the threshold voltage at the “+” terminal of the op-amp?
3. (1 point) What is the function of the op-amp when connected in the buffer
mode (as shown in Fig. 2.2)? Derive the amplifier gain (defined as the ratio of
Vout to Vin) in this configuration?
4. (1 point) Analyze (output versus input voltages) the inverting amplifier circuit
shown in Fig. 2.3. Derive the amplifier gain?
5. (1 point) Analyze (output versus input voltages) the non-inverting amplifier
circuit shown in Fig. 2.4. Derive the amplifier gain?
Experiment 1: (Exercises 1-4, chapter 7) Comparator
1) Follow the pinout diagram (see Fig 7.5 in chapter 7) of LM741CN chip. Place
the chip on the protoboard and complete the voltage comparator circuit as
shown in Fig 2.1 below. Power the op-amp to + (-) 5V using the + (-) 20 V
power supply with protoboard ground connected to the common of the power
supply.
2) Measure the (threshold) voltage at the “+” terminal of the op-amp and compare
with the analysis in Prelab 2. Explain any discrepancies.
3) Use the DC offset on the function generator as V in (Note: Operate the generator
in ‘continuous’ mode) Vary its value from –5 to 5 V. Make a linear plot of Vout
versus Vin. (Be sure you label the axes (with units), mark the scale, and give a
title to the graph!) Compare the result of this plot to the threshold voltage
measured in step (2). How close is the Vout to the values of the + (-) 5V power
supply voltages?
ECE20B Lab, Winter 2002
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Fig. 2.1 Comparator Circuit
Experiment 2: (Exercise 5, chapter 7) Buffer
4) Construct the buffer circuit shown in Fig 2.2.
5) Vary Vin from –5V to 5V. Plot Vout versus Vin. What is Vout when Vin is zero?
Define gain of the amplifier as the ratio of V out to Vin (or the slope of the Vout
versus Vin curve. What the amplifier gain in the non-saturated region? How
does it compare to your analysis in Prelab Question 3.
+5v
_
V
out
Vin
+
-5v
Fig. 2.2 Buffer circuit
ECE20B Lab, Winter 2002
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Experiment 3: (Exercise 6, chapter 7) Inverting Amplifier
6) Construct the inverter circuit shown in Fig. 2.3 using R1 = 1.5 k and RF = 6.8
k. Power the op-amp to + 15 and –15 V respectively. Vary the Vin from –5 V
to 5V. Plot Vout versus Vin. What is the actual amplifier gain? (Slope of curve)
How does it compare with your analysis in Prelab Question 4? What is the
input voltage range over which the op amp is not saturated? Explain your
observations.
Fig. 2.3 Inverting Amplifier circuit
Experiment 4: (Exercise 7, chapter 7) Non-inverting Amplifier
7) Construct the non inverting circuit shown in Fig. 2.4 using the same R1 and RF
as in (6) above. Power the op-amp to + 15 and –15 V respectively. Vary the
Vin from –5 V to 5V. Plot Vout versus Vin. What is the actual amplifier gain?
How does it compare with your analysis in Prelab Question 5? What is the
input voltage range over which the op amp is not saturated? Explain your
observations.
Fig. 2.4 Non-inverting amplifier