Hello, and welcome to the TI Precision Lab Supplement for Op Amp Input and Output Limitations. This lab will walk through detailed calculations, SPICE simulations, and real world measurements that greatly help to reinforce the concepts established in the op amp input and output limitations lecture.

The detailed calculation portion of this lab can be done by hand, but calculation tools such as MathCAD or Excel can help greatly. The simulation exercises can be performed in any SPICE simulator since Texas Instruments provides general SPICE models of the op amps used in this lab. However, the simulations are most conveniently done in TINA-TI, which is a free SPICE simulator available from Texas Instruments. TINA simulation schematics are embedded in the presentation.

Finally, the real world measurements are made using a printed circuit board, or a PCB, provided by TI. If you have access to standard lab equipment, you can make the necessary measurements with any oscilloscope, function generator, and plus or minus 5 volt power supply. However, we recommend the VirtualBench from National Instruments. The VirtualBench is an all-in-one test equipment solution which connects to a computer over USB or Wi-Fi and provides power supply rails, analog signal generator and oscilloscope channels, and a 5.5 digit multimeter for convenient and accurate measurements. This lab is optimized for use with the VirtualBench.

In Experiment 1, we'll determine the effects of input and output limitations in a basic voltage follower or unity gain buffer circuit. First, calculate the input common mode voltage range and output voltage swing for the circuit shown here using the techniques and equations given in the input output limitations lecture. Use the data sheet parameters given on the next slide.

This circuit uses the OPA140. In order to perform the calculations, you need to know the input voltage range and voltage output swing values for that device. Those values are given here. Enter your answers in the table in the middle of the slide. The solutions are already provided to allow you to check your work. Also answer the question at the bottom of the slide. Again, the solution is provided.

The next step is to run a SPICE simulation analysis for the transient output voltage behavior. This will allow us to see the op amp's output voltage response for a specified input signal, which in this case is a 4.5 volts peak 50 kilohertz triangle wave. The necessary TINA-TI simulation schematic is embedded in this slide set. Simply double-click the icon to open it.

To simulate the transient output behavior, click Analysis, then Transient. Run the analysis from 0 microseconds to 40 microseconds. You should see results similar to this. v in is a triangle wave as expected, but v out cannot exceed plus 1.5 volts. This is due to the input common mode voltage limitation of the OPA140.

Make sure to disable the DC power supply before setting up the test PCB. In the VirtualBench software, click the Power button in the DC power supply area to turn off the power. Check the front panel of the VirtualBench unit to make sure the LEDs are off. Also make sure the function generator is off.

To prepare the test board for the measurement, install the jumpers and devices on circuit 5 as shown here. Install JMP17, JMP18, and JMP20, as well as the OPA140 in socket U7. This slide shows the full schematic for circuit 5 on the TI Precision Labs test board. You will use this circuit to measure the effect of input and output voltage range limitations on the OPA140.

For the test board to function properly, it is important that you only install jumpers and devices in circuit 5. Do not install any jumpers or devices in any other circuits on the PCB. Remove any jumpers or devices from the unused circuits and store them in the storage area at the bottom of the test board.

This gives the connection diagram between the TI Precision Labs test board and the National Instruments VirtualBench. Connect the provided power cable to the DC power supply of the VirtualBench and power connector J4 on the test board. Connect VIN2 on the test board to VirtualBench channel FGEN, or function generator. Then connect VIN1 on the test board to VirtualBench oscilloscope channel 1 and VOUT1 on the test board to VirtualBench oscilloscope channel 2.

Next, apply power to the VirtualBench and connect to your computer with a USB cable. The hardware should be detected as a virtual CD drive and you can run the VirtualBench software directly from the drive. Once the software opens, configure it as follows. Set the time scale to 5 microseconds per division with the acquisition mode set to auto. Enable channels 1 and 2 on the oscilloscope and set them to 1x DC coupled mode, 2 volts per division. Enable the function generator and set up the signal as follows.

50 kilohertz frequency, 9 volts peak to peak, 0 volts offset, 50% symmetry, triangle wave. Enable the cursors and set them to plus 1.5 volts and minus 5 volts to show the valid input common mode range. Set the plus 25 volt power supply to plus 5 volts 0.1 amps. Set the minus 25 volts power supply to minus 5 volts 0.1 amps. Press the Power button to turn on the power supply rails.

The expected measurement results are shown here. Compare this oscilloscope display of the VirtualBench to the simulation results from TINA-TI. Also use the cursors on the VirtualBench and TINA-TI tool to measure the voltage where v out becomes limited or clipped. Compare this to your calculation.

The results have already been entered into the table to allow you to check your results. You may have different results in your experiment. As an extra experiment, you can change the input signal frequency to 1 kilohertz and change the time scale to 200 microseconds per division. Now compare the common mode range to the previous 50 kilohertz input signal. What conclusion do you draw from the measurement?

As you can see, there is no noticeable distortion or clipping with the 1 kilohertz signal. This is because the OPA140 is actually rail to rail for low frequencies, but at higher frequencies the common mode performance degrades at about 2 volts from the positive rail.

In Experiment 2, we'll determine the effects of input and output limitations in an inverting amplifier circuit with gain. First, calculate the input common mode voltage range and output voltage swing for this inverting amplifier circuit, again using the techniques and equations given in the input output limitations lecture. Use the data sheet parameters given on the next slide.

This circuit uses the OPA277. In order to perform the calculations, you need to know the input voltage range and voltage output swing values for that device. Those values are given here. Enter your answers in the table in the middle of the slide. The solutions are already provided to allow you to check your work. Also answer the question at the bottom of the slide. Again, the solution is already provided.

Run a SPICE simulation as before, but now using this inverting amplifier circuit with the OPA277. The necessary TINA-TI simulation schematics are embedded in this slide set. Simply double-click the icon to open them. Click Analysis then Transient and run the transient from 0 milliseconds to 2 milliseconds. The input signal to the circuit is a 120 millivolts peak 1 kilohertz triangle wave.

You should see results similar to this. v in is a triangle wave as expected, but v out clips at both the positive and negative ends of the triangle due to output voltage swing limitations. Make sure again to disable the DC power supply before setting up the test PCB. In the VirtualBench software, click the Power button in the DC power supply area to turn off power. Check the front panel of the VirtualBench unit to make sure the LEDs are off. Also make sure the function generator is off.

To prepare the test board for the measurement, install the jumpers and devices on circuit 2 as shown here. Install JMP6, JMP7, and JMP8, as well as the OPA272 and socket U2. This slide shows the full schematic for circuit 2 on the TI Precision Labs Test Board. You will use this circuit to measure the effect of input and output voltage range limitations on the OPA277.

For this measurement, only circuit 2 is used. Do not install any jumpers or devices in any other circuits on the PCB. Remove any jumpers or devices from the unused circuits and store them in the storage area at the bottom of the test board.

The cable connections to the VirtualBench are exactly the same as in experiment 1. No changes are necessary. The VirtualBench instrument set up is very similar to experiment 1. Make only the following changes.

Set the vertical scale of channel 1 to 100 millivolts per division. Keep the vertical scale of channel 2 at 1 volt per division. Set the function generator to a 0.22 volts peak to peak 0 volts offset 50% symmetry triangle wave at 1 kilohertz. Set the time scale to 200 microseconds per division. Turn on the DC power supply and function generator.

Compare the TINA simulation results to your measured results. The shape of the output waveform should look very similar with hard clipping at the top of the waveform. Your device may or may not clip at the bottom of the waveform. That concludes this lab. Thank you for your time.