LTSpice and Lab Orientation – Instruments and Measurements

| June 19, 2015

In this experiment, the student will become familiar with basic circuit implementation in LTSpice and with using the lab equipment to be utilized throughout this course. In LTSpice there will be DC and AC circuit simulation, Transient and AC analysis exercises. In the lab, the equipment to be used includes the ADK oscilloscope, ADK signal generator andADK network analyzer.
In this lab, the student is expected to learn the order lab data should be collected for report purposes, LTSpice and equipment setup and measurements, thus this experiment is structured and step by step instructions are provided to achieve those objectives, later labs will not include this format or level of detail except for special cases.
1.1 Simple DC circuit

Fig.1.1 (Use your handheld calculator for steps 1 and 2 below)
1. Calculate Vout using any appropriate method, e.g. Superposition, Thevenin, .etc.
2. Calculate the current through R2.
3. Simulate the circuit in LTSpice obtaining Vout and the current through R2.

NOTE: ALWAYS paste LTSpice outcomes onto the result section of the lab report
4. In the lab, build the circuit on your breadboard in Fig. 1.1, ensure resistor values by first measuring the resistors using the MS8217 Handheld Multimeter set on Ohms.
Use the Analog Discovery Kit (ADK) to:
5. Measure and record Vout
6. Measure and record the current through R2
Hint: You can measure the current (AC or DC) using one of the following ways:
Measure the voltage across the resistor from the ADK and divide by the value of the resistor
or Measure the current directly using your multimeter.
7. Use % Error to compare the calculated, the LTSpice, and the measured Lab results.

1.2 Simple AC circuit
Fig.1.2
1. Calculate the current through R2 and R4 in the circuit shown in Fig. 1.2.
2. Calculate the voltage across R1, R2, R3 and R4.
3. Define Vrms and calculate Vrms for R2.
4. Simulatethe circuit inLTSpice.
a. Create circuit schematic.
b. Set up for Transient Analysis and obtain in one plot the Current waveforms through R2 and R4.
c. Obtain in one plotthe Voltage waveforms through R1, R2, R3 and R4.
NOTE: ALWAYS paste the resulting Transient Analysis plot onto the result section of the lab report.
5. In the lab, assemble the circuit in Fig. 1.2, ensure resistor values by using the MS8217 Handheld Multimeter to measure them.
6. Set the Function Generator in your ADK.
a. Adjust the ADK function generator VS to provide a 2 Vpp sinewave at 100 Hz frequency.
7. Use the ADK to obtain Voltage across R2 and R4
a. Use the ADK oscilloscope to obtain the Voltage waveforms across R2 and R4. Obtain Vpp, and Vrms of R2 and R4
b. Save the screenshot with VR2, VR4and paste onto the result section of the lab report.
c. Measure the current through R2 and R4 and the voltage across – VR2, VR4 -with the MS8217 multimeter.
8. Document the comparison between the MS8217 multimeter Voltage results for R2 and R4 with the ADK oscilloscope Vrms values for the same resistors. This results should be equal since:
An MS8217 multimeter always gives the RMS value of voltage and current
9. Change the ADK generator waveforms to a Triangular wave and then to a Square wave. In both cases repeat steps 7a, 7b, 7c and 8 above.
10. Calculate the factor between the Vpeak obtained from the ADK oscilloscope and the Vrms value obtained from the ADK multimeter for the Triangular and the Square waves. For example for the Sine wave the factor is 1/√2, since :
Vrms= (1/√2)* (Vpeak) OR Vrms = (1/2*√2) * (V pk-pk)
11. Use % Error to compare the calculated, LTspice and Lab results.

1.3 Low Pass Filter Analysis
Fig. 1.3 shows a low pass filter network. The voltage Gain is the absolute value of the ratio of the output voltage to input voltage. The Gain of this filter is given by the magnitude of the following transfer function:
(1.1)
Fig.1.3 Low Pass Filter Network
1. Calculate the voltage Gain of the filter using eqn. (1.1) (voltage Gain units are V/V).
2. Simulate the circuit in LTSpice (pointers in LTSpice Guide, Creating Schematics)
3. Do Transient Analysis of Vout and Vin (for set up see LTSpice Guide, Transient Analysis). Use the results to:
a. Calculate the filter’s Gain.
b. Obtain the Phase Shift of Vout with respect to Vin.
NOTE: ALWAYS paste the resulting Transient Analysis plot onto the result section of the lab report.
4. Do LTSpice AC Analysis of |Vout/Vin| (for set up see LTSpice Guide, AC Analysis). Use the results to:
a. Use LTSpice to obtain the filter’s Max Gain in dB, that is the max value of:
20 *log10(Abs(Vout/Vin))
b. Obtain the frequency point where:
Gain = Max Gain – 3dB. This is referred as the f3dB point. It is used to determine Bandwidth because it represents the frequency at which Vout has lost half of its original power.
c. Obtain the ω3dB Bandwidth of the Low Pass filter by using:
i. ω3dB = (2*pi*f3dB ) rad/sec
NOTE: ALWAYS paste the resulting AC Analysis plot onto the result section of the lab report.
d. Calculate the ω3dB Bandwidth mathematically by using ω3dB = 1/RC.
e. Compare the values of ω3dB Bandwidth from simulation and calculation.
5. In the lab, build the circuit shown in Fig.1.3, on breadboard but first measure the R and C components to ensure their values, by using MS8217 Handheld Multimeter. (Remember Omega = Resistance, Parallel Lines = Capacitance)
6. Set the ADK Function Generator and adjust it to provide a 2 Vpp sine wave at
10 kHz.
7. Place channel 1 of the ADK oscilloscope at VSand channel 2 at Vout.
8. Display both waveforms on the oscilloscope screen
a. Obtain the relevant measurements, such as Vpp, Vrms and in this case Phase Shift of Vout.
b. Save the screenshot with both waveforms and paste onto the result section of the lab report.
c. Use the measured results of Vout and the known value of Vin to calculate the filter’s Gain.
9. Use % Error to compare the calculated, LTSpice and Lab results.
10. Use the ADK Network Analyzer to plot the gain (dB) and phase (degrees) as a function of frequency from 1kHz to 1MHz. Note: The frequency axis should be log scale (which is the default scale in the Analog Discovery oscilloscope).

1.4 High Pass Filter Analysis
Fig. 1.4 shows a high pass filter network. The voltage Gain is the absolute value of the ratio of the output voltage to input voltage. The Gain of this filter is given by the magnitude of the following transfer function:
(1.2)
Fig.1.4 High Pass Filter Network
Procedure:
1. Calculate the voltage Gain of the filter using eqn. (1.2) (voltage Gain units are V/V).
2. Simulate the circuit in LTSpice .
3. Do Transient Analysis of Vout and Vin. Use the results to:
a. Calculate the filter’s Gain.
b. Obtain the Phase Shift of Vout with respect to Vin.
NOTE: ALWAYS paste the resulting Transient Analysis plot onto the result section of the lab report.
4. Do AC Analysis of |Vout/Vin|. Use the results to:
a. Obtain the filter’s Max Gain in dB, that is the max value of:
20 *Log10(Abs(Vout/Vin))
b. Obtain the frequency point where:
Gain = Max Gain – 3dB. This is referred as the f3dB point. It is used to determine Bandwidth because it represents the frequency at which Vout has lost half of its original power.
c. Obtain the ω3dB Bandwidth of the High Pass filter by using:
ii. ω3dB = (2*pi*f3dB ) rad/sec
NOTE: ALWAYS paste the resulting AC Analysis plot onto the result section of the lab report.
d. Calculate the ω3dB Bandwidth mathematically by using ω3dB = 1/RC.
e. Compare the values of ω3dB Bandwidth from simulation and calculation.
5. In the lab, build the circuit shown in Fig.1.4, and measure the R and C components to ensure their values using the MS8217 Multimeter
6. Set the Function Generator and adjust it to provide a 2 Vpp sine wave at 1 kHz.
7. Place channel 1 of the ADK oscilloscope at VSand channel 2 at Vout.
8. Display both waveforms on the oscilloscope screen.
d. Use the Measurement function to obtain the relevant measurements, such as Vpp, Vrms and in this case Phase Shift of Vout.
e. Save the screenshot with both waveforms and paste onto the result section of the lab report.
f. Use the measured results of Vout and the known value of Vin to calculate the filter’s Gain.
9. Use % Error to compare the calculated, LTspice and Lab results.
10. Use the ADK Network Analyzer to plot gain (dB) and phase (degrees) as a function of frequency from 10Hz to 100kHz.

Post-lab Questions: (These are theoretical questions. Use LTSpice and calculator)
1. With respect to AC parameters, what type of Voltage or Current measurement is taken with digital multimeters and what types with oscilloscopes?
2. Why is it dangerous to short a voltage source?
3. Use LTSpice to implement and discuss the outcomes of the followings:
a. Modifying the resistors, R1 and R2, to be 10kΩ in the simple AC circuit shown in Fig. 1.2, instead of 1kΩ.
b. Applying a sinusoidal input signal of 20Vpp and 1 kHz in the low pass filter circuit shown in Fig. 1.3, as a substitute of 2Vpp and 10 kHz.
Note: Always do Transient and AC analysis when there are frequency dependent components in the circuit.
c. Modifying the resistor R to be 2kΩ in the High Pass Filter circuit shown in Fig. 1.4, instead of 20 kΩ.
Note: Always do Transient and AC analysis when there are frequency dependent components in the circuit.
4. Determine the nominal value of the resistor, along with its tolerance, equivalent to the following colors of the bands. Use Table 1.1 and eqn. (1.3).
i. Band A, brown; band B, black; band C, red; band D, gold.
ii. A, B, and C bands are yellow and band D is gold.
iii. If the nominal value of the resistor is 10Ω, what would be the best choice of the color bands?

R = (10A+B) C ± D% (1.3)

Table 1.1 Color codes for resistors
Band A Band B Band C Band D
Color First
Significant
digit Second
Significant
digit Color Multiplication Color Resistance
Tolerance
(%)
Black 0 0 Black 1 No color
(or black) ±20
Brown 1 1 Brown 10 Silver ±10
Red 2 2 Red 100 Gold ±5
Orange 3 3 Orange 1,000 White or green ±5
Yellow 4 4 Yellow 10,000
Green 5 5 Green 100,000
Blue 6 6 Blue 1,000,000
Purple 7 7
Gray 8 8 Silver
White 9 9 Gold

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