ECEN 313
Stephen Schultz
Winter 2009
The Electronic Amplifier
Objectives:
1. Familiarize the student with the operation of a simple electronic amplifier.
2. Review the use of test equipment and test methods for performing basic amplifier
measurements.
3. Examine the frequency response of an op-amp based inverting amplifier.
Equipment:
1.
2.
3.
4.
5.
Tektronix TDS 340A oscilloscope
Signal generator
Two power supplies
LF347 IC operational amplifier
Miscellaneous components
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. In Fig. 1, determine the effective resistance seen by C1.
2. Determine the form of the transfer function
. You do not need to include any
numerical values.
3. Determine the numeric value for the lower 3-dB frequency, fL, of the amplifier.
4. Obtain an approximate value for the gain-bandwidth product (GBW) of the LF347 op amp
from a product datasheet. You should get a datasheet off of the internet.
Figure 1
Procedure
1. Simulate the circuit shown in Fig. 1. Determine the midband gain, upper and lower 3dB
frequencies.
2. Compare the simulated results to the values obtained during the preliminary work.
3. Determine the input voltage amplitude that will produce a 10Vpp output.
4. Connect the circuit as shown in Fig.1. Figure 2 shows the pin-out. Verify that this pin out
is the same as that of the specification sheet that you downloaded off of the internet.
5. Apply a 4 kHz sinusoidal signal to the input and measure the output. Plot the gain as a
function of input voltage. Determine the maximum undistorted output signal. You will
need to use a voltage divided in order to get a small enough input voltage.
6. Set the input to produce an output level of 10 Vpp. Accurately measure the input and
output levels at 4 kHz to determine the midband gain of the circuit.
7. Compared the measured midband gain to the simulated value.
8. Vary the frequency of the input signal to observe low and high frequency roll-off and then
record the upper and lower 3 dB frequencies. Take sufficient data to (1) permit the accurate
construction of the frequency response near the corner frequencies, and (2) determine the
slope of the low and high frequency roll-off.
9. What is the measured gain-bandwidth product (GBW)?
10. Change the input signal to a square wave and set the amplitude such that the output is not
driven to it maximum swing. Vary the frequency to sag. Set and record the frequency that
will produce 10% sag. To do this, display the square wave from your circuit output on the
oscilloscope. Vary the frequency until an obvious decay in the square wave appears.
Continue to vary the frequency until the decay reaches 90% of the original amplitude.
Demonstrate the waveform with 10% sag to a TA and obtain a completion stamp.
11. Measure the 10%-90% rise time of the square wave output.
12. Compute the expected bandwidth of the amplifier based on the rise-time measurement.
Compare it to the measured bandwidth. Remember that tr=2.2/,  is the upper 3dB
frequency.
13. Calculate the expected sag and compare with the 10% sag value you measured. Derive an
equation for the sag. Hint: use the equation
.
Figure 2. LF347 pin-out.