Download ECE 2205 Lab 4 Operational amplifier circuits

ECE 2205 Lab 4
Operational amplifier circuits
In the lab, we will use the 741 operational amplifier, which has been around for decades. It is an
integrated circuit (meaning that all of its components are built into a single piece of silicon) that
can be packaged in a variety of ways. The package we will use is the 8-pin DIP (dual in-line
package), which plugs easily into the superstrip circuit boards. The package has more pins than
are necessary. We only need to use five pins — inverting and non-inverting inputs, output, and
the positive and negative supply voltages. Note that there is no specific ground connection. The
ground for the op amp circuit is defined by the common connection for the two power supplies.
In some circumstances, we may connect one of the inputs to ground. The pin arrangements for
the 741 package are shown below.
Wire up each of the five circuits shown below and apply the required input voltage(s). For each
of the circuits, use power supply voltages of +15 V and –15 V for the op amps. Also, be sure to
measure the values of the resistors used in your circuits. For each of the circuits, we will apply a
simple sine wave to the input of the circuit and then observe the (hopefully amplified) output on
the oscilloscope.
Bring a flash drive to lab for collecting scope traces or you can take a picture using your smart
phone.
Have your lab instructor check the wiring before you turn on DC supplies for the op amp. It’s a
common mistake to have the positive and negative supplies reversed. Applying the wrong
polarity to the power connections will likely burn out the op amp.
1
ECE 2205 Lab 4
Non-inverting amplifier
Build the non-inverting amplifier circuit
shown at right. Measure the resistors, so that
you know their precise values.
+
–
+
vS
–
For VS, use the function generator set to a
sinusoid with frequency of 1000 Hz and
amplitude of 1 V.
vo
R2
10 k
R1
1k
a. Calculate the expected gain, G = vo/vs for the circuit.
b. Measure the gain by measuring the output voltage and input voltage with the multimeter
and calculating the ratio.
c. Observe the input and the output together on the oscilloscope. Save a copy of a clear trace
to put in your report.
d. Increase the amplitude of the input sinusoid to 1 V. Observe the input and output together
on the oscilloscope again. Note the differences in the output from part c. Save a copy to
put into your report.
Inverting amplifier
R2
Build the inverting amplifier circuit shown at
right. Measure the resistors, so that you
know their precise values.
R1
2.2 k
For VS, use the function generator set to a
sinusoid with frequency of 1000 Hz and
amplitude of 0.25 V.
vS
+
33 k
–
+
vo
–
a. Calculate the expected gain, G = vo/vs for the circuit.
b. Measure the gain by measuring the output voltage and input voltage with the multimeter
and calculating the ratio.
c. Observe the input and the output together on the oscilloscope. Save a copy of a clear trace
to put in your report.
2
ECE 2205 Lab 4
Summing amplifier
RF
Build the summing amplifier circuit shown
at right. Measure the resistors, so that you
know their precise values.
VAC
Ri1 1 k
VDC
Ri2 10 k
10 k
–
+
vo
For VAC, use the function generator set to a sinusoid with frequency of 1000 Hz and amplitude of
0.5 V. For VDC, use the third DC output (0-5V) of the triple DC supply – be sure to connect its
ground connection to the ground for the positive and negative supplies.
a. Calculate the expected output function for the circuit.
b. Observe the input and the output together on the oscilloscope. Note the summing action
by varying the DC voltage from 0 to 3 V and noting the effect on the output. Record
oscilloscope traces for two different values of VDC.
c. Measure the gain of the ac path by connecting making VDC = 0 (connect it to ground) and
measuring the output and the AC input (VAC) and calculating the ratio.
Difference amplifier
R2 10 k
Build the difference amplifier circuit shown
at right. Measure the resistors, so that you
know their precise values.
vb
R1 1 k
va
For the source voltage, use the function
generator set to a sinusoid with frequency of
1000 Hz and amplitude of 0.5 V.
R3 2.2 k
–
+
vo
R4
22 k
a. Calculate the expected output for the circuit, in terms of the two input voltages and the
resistors.
b. Set vb to 0 V (connect it to ground) and connect the source to va. Measure the gain, G = vo/
va by measuring the output voltage and input voltage with the multimeter and calculating
the ratio. Observe the input and the output together on the oscilloscope. Save a copy of a
clear trace to put in your report.
c. Swap the the inputs (connect va to ground and vb to the sinusoid). Measure the gain for this
path. Observe the input and the output together on the oscilloscope. Note the difference
between this trace and the one seen in part b. Save a copy of a clear trace.
d. Lastly, connect va and vb both the sinusoidal source. Measure and observe the output
voltage in case. (What happened to it!?)
3
ECE 2205 Lab 4
Cascaded amplifiers
Choose a second op-amp from your component bag and build the circuit with two
cascaded amplifiers shown below. Measure the resistors, so that you know their precise
values.
1
vS
2
R4
+
R2
–
68 k
R3
+
–
–
+
10 k
vo
4.7 k
R1
1k
For VS, use the function generator set to a sinusoid with frequency of 1000 Hz and amplitude of
0.25 V.
a. Calculate the expected gain, G = vo/vs for the circuit.
b. Measure the gain by measuring the output voltage and input voltage with the multimeter
and calculating the ratio. Also, measure the gain for each stage independently.
c. Observe the input and the output together on the oscilloscope. Save a copy of a clear trace
to put in your report.
Clean up
When finished, be sure to turn off the equipment, keep your own parts in your component bag,
return the wires to the wire racks, clean off any debris from the lab benches.
Report
Prepare a report that includes the calculated gains and/or output functions, measured gain
values, and oscilloscope traces for each of the circuits, as described in the instructions.
4
ECE 2205 Lab 4
5