# Maximizing Op Amp Bandwidth

```ECEN 313
AMPLIFIER DESIGN TO MAXIMIZE BANDWIDTH
Objectives
In this lab you are to use the op amp chips that come in your kit (LF 347) to construct an
amplifier with a specified overall gain while achieving maximum overall bandwidth.
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. Design an amplifier chain with a total gain of 80 V/V and an upper 3-dB frequency greater
than 250 kHz. Use a gain bandwidth product of GBW=2.2MHz.
Laboratory Work
A microphone is to be simulated by a 100 mV peak source with a 10 k resistor in series. The
load is a 2 kresistor. Both source and load are to be ac coupled (capacitor coupled) to the
amplifier chain. Figure 1 shows a schematic of the system.
50
10k
Multi-Stage
Amplifier
0.1V
+
8V
2k
Figure 1
The output voltage across the load should be 8 V peak. The lower 3-dB point should be below
300 Hz. The upper 3-dB frequency should exceed 250 kHz. Use the fewest number of stages
possible. In other words, your design should optimize overall bandwidth while realizing a gain
of 80 V/V.
Important note: Every time you use an op amp chip it must have the power supply pins
bypassed with a capacitor to ground. This is standard practice in industry and an op amp
should never be used without bypassing. Put capacitors located as close as possible to the IC
from the positive supply pin to the ground pin and from the negative supply pin to the ground
pin. Typical values of capacitance are 0.01 F to 1 F---non-electrolytic.
Suggestions:
 Measure the GBW (gain-bandwidth product) of your op amps. Are the GBW of all of
the op amps on the chip the same?
 Build your first stage and characterize it before moving on to a two-stage amplifier
stage. Likewise, characterize your two-stage amplifier chain before moving onto a 3
stage.
 Measure the gain after each stage to make sure that each Op Amp is working properly
and is connected correctly. Compare all measurements to your calculations to make
sure things are working properly.
 Tweak the gain to be the desired gain by getting it close with three identical stages and
then adjust the gain of one stage.
Be sure to include the following in the lab write-up.
1. Schematic of the circuit that you built.
2. Pspice simulation of your design.
3. Measurements of mid-band gain, lower and upper 3-dB frequencies. These should be
oscilloscope plots. The midband gain needs to within10% of stated specification.
4. Bode plot of your design. Be sure to include dots for your actual measurements. What is
the slope of the bode plot for low and high frequency?
5. List the error between the simulation and the measurement. Be sure to discuss the
differences.
```