In this lab we will demonstrate the inverse relationship between
closed-loop gain and bandwidth in conventional operational amplifiers,
for both non-inverting and inverting configurations.
1. Construct a non-inverting amplifier using a 741 op amp and
measure its small-signal 3 dB bandwidth for closed-loop gains
of 1, 10, and 100. (By small signal, we mean that the output
amplitude is sufficiently small that the slew rate of the op amp
is not a limiting factor at the 3 dB frequency.) What is the
feedback ratio b and expected value
of the bandwidth in each case? What is the unity gain frequency
of the op amp? Are you able to determine the low-frequency open
loop gain Ao?
2. A unity-gain inverting amplifier has half the bandwidth of a unity gain non-inverting amplifier (a follower). This is because the feedback ratio of the inverting amplifier is the same as that of a non-inverting amplifier of gain 2. Measure the bandwidth of a non-inverting x2 amplifier and an inverting x1 amplifier and see if they agree, and compare with the bandwidth of the follower amplifier from part 1. Sketch the Bode plot for
each of the three amplifiers.
3. What bandwidth would you expect for inverting amplifiers of
gain = 10 and 100? Measure and compare with theory. Sketch the
frequency response on a Bode plot, showing how it differs from
that of a non-inverting amplifier of the same gain.