Download Preliminary Work

ECEN 313
STEPHEN SCHULTZ
WINTER 2009
DOCUMENTING, CONSTRUCTING, AND DEBUGGING A
CIRCUIT
Objective: This experiment is intended to teach several principles that will be used in most of
the laboratory experiments that follow. These principles include:
1. Drawing a schematic in an acceptable design format.
2. Constructing a breadboard circuit and verifying the constructed circuit for accuracy by
comparison with the schematic (backtrace).
3. DC analysis by hand calculation of simple circuits.
4. Using a SPICE simulation to predict expected circuit performance and verify
breadboard construction.
Preliminary Work
Please complete the preliminary work before coming to lab. This will greatly reduce the
amount of time spent in the lab and will allow you to get more meaningful help from the TAs.
1. Make an extra copy of your schematics (Figs. 1-3) using a Xerox copier or equivalent
means.
2. Calculate all dc node voltages for your circuit using ohm's law/voltage divider principles, or
nodal analysis. Label the node voltages on copy 1 of your schematic (this will produce a
“dc voltage map” of your circuit).
Vout
+
+
22k
-15V
-
+
15V
V-
V+
LF347/301/TI
-
-
10k
+
5V
Figure 1
PROCEDURE:
1. DC Circuit
a. Simulate the circuit (Fig. 1) in SPICE.
b. Compare the simulation results to the DC voltage map.
c. Fix or justify any discrepancies between the voltages calculated by hand and the
simulation results.
Vout
-15V
22kW
-
+
15V
V-
V+
LF347/301/TI
1mF
10kW
50W
2Vp
Figure 2
2. AC Circuit
a. Replace the dc voltage input source in your SPICE model with a 1mF capacitor, a
50W resistor, and a 2 V pk AC voltage source (VAC part in PSpice). The 50W
resistor corresponds to the Thevenin equivalent resistance of the signal generator.
(The schematic is shown in Fig. 2.) Always identify an ac voltage as X volts pk or
Y volts pk-pk.
b. Simulate your circuit for its expected frequency response. Do an AC sweep in
PSpice. What are the 3 dB low and high frequency roll-offs (fH and fL)?
c. Construct your circuit (Fig. 2) on a breadboard/plugstrip per your schematic. Figure
4 provides the pin-outs for the LF347 Op Amp chip. After your circuit is
constructed and before it is tested, backtrace your circuit from the breadboard to the
schematic. Trace each line on copy 2 of your schematic using a colored pencil or
highlighter pen when it has been connected. The backtrace is complete when all
lines have been marked on the schematic. Correct any wiring problems discovered.
Note that all op amps should have 0.1 microfarad capacitances from both power
supply pins on the chip to ground.
d. Apply a 2 V pk, 1KHz sinusoid to the input of your circuit. Measure the resulting
output. Never record an ac voltage as Z volts. Repeat for frequencies of 10KHz,
100KHz, and 1 MHz.
e. Compare the measured results to the SPICE simulation
Vout
-15V
1nF
22kW
-
+
15V
V-
V+
LF347/301/TI
1mF
10kW
50W
2Vp
Figure 3
f. Add a 1nF capacitor in parallel with the 22kW feedback resistor in your SPICE
simulation (See Fig. 3). Determine the upper and lower 3dB frequencies.
g. Model the resulting output voltage for a 2Vpk 20kHz sinusoidal input.
i. From the AC sweep analysis determine what the output voltage amplitude
should be.
ii. Simulate the voltage output. This is accomplished by replacing the VAC
source with VSIN source with VAMPL=2 and FREQ=20k. The transient
analysis is then done rather than the AC sweep. What is the voltage
amplitude?
h. Add the capacitor to the circuit. Apply a 2 Vpk, 20KHz sinusoidal voltage signal
to the input of your circuit. Measure the resulting output.
i. Compare the measured results to the SPICE simulation.
Figure 4. LF347 pin-out.