Download Experiment 10: Inverting Amplifier

Experiment 10:
Inverting Amplifier
With Modifications that Require the
Use of the Velleman Oscilloscope
Figure 1:
Circuit Diagram for Inverting Amplifier
Additional Steps
• Modeling in PSpice
– Simulate the transient response of the inverting
amplifier circuit using
• Part E, a voltage controlled voltage source
– The difference in voltage between the two input terminals of an
op amp cause an output voltage to be generated.
» Ideal Op Amp model
• Part LM324
» Close to a real Op Amp model
– The sinusoidal voltage source that must be used for
a transient analysis is Part Vsin.
Circuit A with Part E:
Schematics
Op Amp Equivalent Circuit
vd = v2 – v1
A is the open-loop voltage gain
v2
v1
Typical Op Amp Parameters
Parameter
Variable
Typical Ranges
Ideal Values
Open-Loop
Voltage Gain
A
105 to 108
∞
Input
Resistance
Ri
105 to 1013 W
∞W
Output
Resistance
Ro
10 to 100 W
0W
Supply Voltage
Vcc/V+
-Vcc/V-
5 to 30 V
-30V to 0V
N/A
N/A
Voltage Transfer Characteristic
Set Open Loop Gain
• Double click on symbol and set GAIN to at
least 100,000
– Typical open loop gain of an op amp is 105-108 V/V
Setting the Attributes on Vsin:
Schematics
Double click on the symbol for V1.
A pop-up window will open.
Change:
VOFF (the dc offset
voltage) to 0V.
VAMPL to 5V.
FREQ to 500Hz.
Circuit A with Part E:
Capture
Open Loop Gain
• Double click on symbol for Part E.
• Set GAIN in Property Editor pop-up window to
at least 100,000.
Setting Attributes on Vsin:
Capture
• Double click on the labels (VOFF, VAMPL, and
FREQ) individually in schematics and change
their value in the pop-up window that opens.
Setting Attributes on Vsin:
Capture
• Or, click on the symbol for Vsin and change the
values for the attributes in the Property Editor
pop-up window.
– FREQ is at the left side, VOFF and VAMPL are at
the far right side.
Scroll right to
find VOFF and
VAMPL
Circuit B with LM324:
Schematics
Simulation Set-up:
Schematics
Final Time
should be 3-5
times the period
(T) of V1.
T = 1/f where f
is the frequency
of the sinusoidal
signal.
Simulation Profile:
Capture
Plot of the input voltage and output
voltage as a function of time
Modifications to Measurement
Section: New Circuit
Cables
• The connections to the Velleman scope are
BNC (Bayonet Neill-Concelman) connectors.
– You will need to use 3 BNC cables with either the
alligator clips or the IC clips to make your
connections between the scope and your circuit.
Input Voltage Source
• Use the sine wave generator on the Velleman
scope.
– Set the amplitude of the sine wave to 5V
• Note that the amplitude on the Velleman scope is actually
peak-to-peak so you should actually make this 3V.
– Set the frequency of the sine wave to 500Hz.
– Connect BNC cable to function generator (bottom BNC
connection).
• Clip red probe to end of R2.
• Clip black probe (ground) to end of R1.
Voltage Measurements using
Oscilloscope
• Channel 1:
– Red probe placed between function generator and
R2.
– Black probe connected to same point as the black
wire from the function generator.
• Channel 2:
– Red probe placed between output of the LM 324
and the feedback resistor, R5.
– Black probe connected to same point as the black
wire from the function generator.
Measurements
1. As suggested in lab manual, set trim pot value such that
the output voltage of the op amp is equal to -3V when the
input voltage is +1.5V.
– Take a screen shot of the input and output voltage as a function
of time, displaying at least 3 cycles.
– Remove R5 from the circuit. Measure and record the resistance
between pins 1 and 2.
– Measure the output voltage at the following input voltages:
• 0V, +/-1V, +/-2V, +/-3V, +/- 4V, +/-5V, and +/-6V
– use cursors in scope program
– Plot the output voltage as a function of the input voltage.
• Determine
– the gain of the inverting amplifier in the linear region of the voltage transfer
characteristic using a least squares determination of the slope in the linear
region
– the output voltage at the positive and negative saturation regions.
Measurements
2. Set trim pot value such that the output voltage of the op
amp is equal to -4.5V when the input voltage is +1.5V.
– Take a screen shot of the input and output voltage as a function
of time, displaying at least 3 cycles.
– Remove R5 from the circuit. Measure and record the resistance
between pins 1 and 2.
– Measure the output voltage at the following input voltages:
• 0V, +/-1V, +/-2V, +/-3V, +/- 4V, +/-5V, and +/-6V
– use cursors in scope program
– Plot the output voltage as a function of the input voltage.
• Determine
– the gain of the inverting amplifier in the linear region of the voltage transfer
characteristic using a least squares determination of the slope in the linear
region
– the output voltage at the positive and negative saturation regions.
Measurements
3. Set trim pot value such that the output voltage of the op
amp is equal to -6V when the input voltage is +1.5V.
– Take a screen shot of the input and output voltage as a function
of time, displaying at least 3 cycles.
– Remove R5 from the circuit. Measure and record the resistance
between pins 1 and 2.
– Measure the output voltage at the following input voltages:
• 0V, +/-1V, +/-2V, +/-3V, +/- 4V, +/-5V, and +/-6V
– use cursors in scope program
– Plot the output voltage as a function of the input voltage.
• Determine
– the gain of the inverting amplifier in the linear region of the voltage transfer
characteristic using a least squares determination of the slope in the linear
region
– the output voltage at the positive and negative saturation regions.
Measurements
• Measure exact values of V+ and V- powering
the LM 324 op amp.
Tabulate Results
Vout when Vin Gain from
is equal to 1.5V Analysis
Measured
Value of R5
Gain from
Least Square
Fit of Data
% Deviation of
the Gain
-3V
-4.5V
-6V
Vout
when
Vin is
equal to
1.5V
-3V
-4.5V
-6V
Averaged Measured Averaged Measured % Deviation
Measured Value of
Measured Value of
for positive
Positive
V+
Negative
Vsaturation
Saturation
Saturation
voltage
Voltage
Voltage
% Deviation
for negative
saturation
voltage
Discussion Section
• Compare the gains found in Analysis Section and the
measured results.
– Explain any discrepancies
• Explain the major differences between the two PSpice
simulations.
• Compare the averaged positive and negative saturation
voltages with the measured values of the power
supplies.
– Does the saturation voltage depend on the amplifier gain
(within experimental error)?
– Does the saturation voltage agree with that specified in
the LM 324 data sheet (find on-line)?