Lab 4 – EE 420L
Authored by: Daniel Senda
Email: sendad1@unlv.nevada.edu
Spring 2019
Due: 02-27-2019

1) Introduction

This lab is intended to help students learn how to set up the different topologies of op-amps. It also shows students how to read additional parameters from the datasheet including gain bandwidth product and slew rate.

2) Pre-Lab Description

The pre-lab required the student to complete the following before proceeding with lab:

- Watch the op_amps_II video and read review.

- Simulate the circuits given in the op_amps_II.zip file and understand operation.

- Read the entire lab write-up before going to class.

3) Description of Lab Procedures

This lab utilized the LM324 operational amplifier (op-amp). The datasheet can be found here.

For the first part of the lab, the student was instructed to estimate the bandwidths for non-inverting op-amps topologies having gains of 1, 5, and 10 using the datasheet. The following image is from the datasheet showing the value of the gain bandwidth product, which is used to calculate the bandwidth with respect to gain.

In addition, the student had to experimentally verify the calculated bandwidths assuming a common-mode voltage of 2.5 V.

Gain of 1 (Non-Inverting Topology):
Calculated bandwidth with unity gain (gain of one) using the non-inverting topology.

The student built the following circuit on the breadboard to get experimental data to verify the calculated value.

Non-inverting topology (Gain 1) circuit:

After powering the circuit and adjusting the parameters of the lab equipment, the following waveform was created.

Oscilloscope waveform results:

The yellow/orange signal is Vin and the blue input is Vout (this signal color coding is kept constant throughout this entire lab). As can be noted, the magnitude of the output is about 0.707 the input voltage at the frequency of 1.3MHz. This is the 3dB point where the output signal starts to roll off. These experimental results support the calculated value.

Gain of 5 (Non-Inverting Topology):
Calculated bandwidth with gain of 5 using the non-inverting topology.

The student made the following calculations figure out which resistor values to use when building the circuit that would have a gain of 5.

Non-inverting topology (Gain 5) circuit:

Oscilloscope waveform results:

The results from the oscilloscope show the 3dB point where Vout starts to roll-off is at 190kHz. The experimental data is different than the calculated value, and this difference can be traced back to the variation of electrical components used to build the circuit. Also, the op-amp is not ideal.

Gain of 10 (Non-Inverting Topology):
Calculated bandwidth with gain of 10 using the non-inverting topology:

The student made the following calculations figure out which resistor values to use when building the circuit that would have a gain of 10.

Non-inverting topology (Gain 10) circuit:

Oscilloscope waveform results:

The results from the oscilloscope show the 3dB point where Vout starts to roll-off is at 96kHz. The experimental data is different than the calculated value. Also, the op-amp is not ideal and the difference here can also be traced back to the variation of electrical components used to build the circuit.

For the second part of the lab, the student was instructed to estimate the bandwidths for inverting op-amps topologies having gains of -1, -5, and -10 using the datasheet. The student also had to experimentally verify the calculated bandwidths assuming a common-mode voltage of 2.5 V.

Gain of -1 (Inverting Topology):
Calculated bandwidth with a gain of negative one using the inverting topology.

The student built the following circuit on the breadboard to get experimental data to verify the calculated value.

Inverting topology (Gain -1) circuit:

Oscilloscope waveform results:

As can be noted, the magnitude of the output is about 0.707 the input voltage at the frequency of 800kHz. This is the 3dB point. These experimental results are off from the calculated results. The could be due to the fact that the circuit is not ideal.

Gain of -5 (Inverting Topology):
Calculated bandwidth with a gain of negative five using the inverting topology.

The student built the following circuit on the breadboard to get experimental data to verify the calculated value.

Inverting topology (Gain -5) circuit:

Oscilloscope waveform results:

The results from the oscilloscope show the 3dB point where Vout starts to roll-off is at 150kHz. The experimental data is different than the calculated value. This difference could be because of the variation of electrical components used to build the circuit.

Gain of -10 (Inverting Topology):
Calculated bandwidth with a gain of negative ten using the inverting topology.

The student built the following circuit on the breadboard to get experimental data to verify the calculated value.

Inverting topology (Gain -10) circuit:

Oscilloscope waveform results:

The results from the oscilloscope show the 3dB point where Vout starts to roll-off is at 82kHz. The experimental data is different than the calculated value. The op-amp is not ideal which could cause the difference.

The last part of the lab had the student create two circuits to measure the slew rate of the LM324. One of them had to make use of a pulse waveform while the other had to make use of a sine wave.

Slew rate info from datasheet:

Picture of the circuit:

The same circuit was used for both versions, the only difference was the input voltages. This first input voltage is a pulse wave and the other is a sine wave.

Slew rate with pulse wave input:

Slew rate with sine wave input:

The slew rate that was measured experimentally was close to what the datasheet has.

This concludes lab 3. (Lab was backed-up on an external drive)

Additional Links

→ Return to listing of lab reports
→ Daniel’s CMOS homepage
→ Dr. Baker’s CMOS homepage