EE 2212

Fall 2018

13 September 2018

Experiment 2: Basic Operational Amplifier Circuits

Report Due: 20 September February

Note 1: I will provide an overview of the op amp SPICE models at the beginning of the laboratory. We will be discussing time domain and frequency domain analysis.

Note 2: Your frequency-independent designs will be used as the basis for analog active LPF, HPF, and Band-Pass filter designs in in Experiment 3, 20 September.

PURPOSE

To implement the designs of:

Ø Two versions of an inverting operational amplifier (Figures 1 and 3)

Ø A non-inverting operational amplifier

Ø A cascade of an inverting and non-inverting amplifier.

GENERAL COMMENTS

Run the SPICE time-domain simulation with a VSIN generator and the frequency-domain simulation with a VAC generator. Use the μA741 model in the eval.slb library. Print the waveforms of the inputs and outputs on the same set of axes. You will need the following information from your SPICE simulations in order to complete this lab:

Ø TRANSIENT analysis for a sinusoidal input

Your hardware realizations designs must not incorporate series and parallel resistors to meet the voltage gain specifications. It is more desirable to come close with standard value components and use the exact measured numbers in your circuit simulation.

PRELAB

Ø Specify the component values to meet the indicated specifications for Circuits 1 and 2 . You should come to the lab with a list of the components you will need to meet the specifications. You might refer to your EE 2006 notes and labs since you have worked with op amps in that course.

The derivation, in your notebook, of the voltage gain Vo/Vs for Circuit 3 using summing point constraints. This is also a good exercise in the use of nodal analysis. (R2, R3, R4 node)

PROCEDURE

Refer to the mA741 data sheet on the class WEB page uA741.pdf. Observe, you are using the 8-pin DIP (Dual-Inline Package), second package style from the top. This package is also sometimes called the MINIDIP. Also note that the mA741 has certain requirements with respect to allowed resistance values that includes all resistors in your design must be greater than or equal to 2 kW. Do not include the 10 kW offset voltage potentiometer.

Use ± 12 volts for the power supplies. Verify that the polarities are correct or you will create a classic embarrassing odor not correctable with Old SPICE (pretty good pun!) body wash.

Your designs should be supported analytically and by SPICE simulation results. You should record all key oscilloscope waveforms on your flash drive as support for your laboratory report.

1. For Figure 1. Design and test an inverting amplifier with a low-frequency voltage gain of 20 dB.

Ø Start with a 1 kHz sinusoidal input voltage. The input voltage level is not critical as long as you do not observe clipping on your output waveform.

Ø Experimentally verify your design and simulation results in the time domain.

Ø Experimentally determine the input signal level when “clipping” of the output waveforms occurs.*

Ø Observe the resultant transfer characteristic. The transfer characteristic is a plot of Vout versus Vin. In order to see the transfer characteristic on the oscilloscope, you will need to change the display to “XY” mode. Select the “Display” key and select “XY Display” from the menu. Switch to “Triggered XY” mode. You may use the scale controls to adjust the axes accordingly. Also verify your voltage gain and phase shift measurements using the transfer characteristic. Note the negative slope is indicative of the low frequency 180°of phase shift in an inverting amplifier.

Ø Measure and plot the voltage gain in dB as a function of frequency, and q(jf), which is the phase shift as a function of frequency, through the amplifier circuit, and compare your results with the SPICE AC simulation. Extend your measurements to a 10 kHz or so. Plot the results as you take your measurements. Note that if the Greek (Theta) q(jf) printed out as q(jf), your WEB browser and/or word processing program does not translate symbol font correctly.

*Go slow in increasing the amplitude of Vs! Do not overdo the input voltage to observe clipping because if your input becomes too large, you will damage the mA741.

Figure 1 Inverting Operational Amplifier Circuit

2. For Figure 2. Design and test a non- inverting amplifier with a low-frequency voltage gain of 14 dB.

You are essentially repeating the procedure for Figure 1.

Ø Start with a 1 kHz sinusoidal input voltage. The input voltage level is not critical as long as you do not observe clipping on your output waveform.

Ø Experimentally verify your design and simulation results in the time domain.

Ø Experimentally determine the input signal level when “clipping” of the output waveforms occur.*

Ø Observe the transfer characteristic. The transfer characteristic is a plot of Vout versus Vin. In order to see the transfer characteristic on the oscilloscope, you will need to change the display to “XY” mode. Select the “Display” key and select “XY Display” from the menu. Switch to “Triggered XY” mode. You may use the scale controls to adjust the axes accordingly. Also verify your voltage gain and phase shift measurements using the transfer characteristic. Note the positive slope indicative of the low frequency 0° of phase shift.

Ø Measure and plot the voltage gain in dB as a function of frequency, and q(jf), which is the phase shift as a function of frequency, through the amplifier circuit, and compare your results with the SPICE AC simulation. Extend your measurements to a 10 kHz or so. Plot the results as you take your measurements.

*Go slow in increasing the amplitude of Vs! Do not overdo the input voltage to observe clipping because if your input becomes too large, you will damage the mA741.

Figure 2 Non-Inverting Operational Amplifier Circuit

3. Cascade amplifier topology

Connect the input of Circuit 2 to the output of Circuit 1 which results in a cascade amplifier configuration. Your cascade gain will be 20 dB + 14 dB = 34 db.

Ø Set the input frequency to a 1 kHz sinusoidal input voltage. The input voltage level is not critical* as long as you do not clip your output waveform. Note that the magnitude of your cascade gain is about 50, i.e. 34 dB.

Ø Experimentally verify your design and simulation results in the time domain.

Ø Measure 20 log|A(jf), the voltage gain in dB, and the phase, q(jf) and compare your results with the SPICE AC simulation. Extend your measurements to 10 kHz or so. Plot your results as you collect the data.

Ø Observe the transfer function and verify the voltage gain and low frequency phase shift from the slope at 1 kHz.

*Note that your input level will be much less than used for either circuits 1 or 2 since the cascade gain is now 34 dB.

4. Another Inverting Amplifier Configuration. Refer to Figure 3.

Figure 3 Another Inverting Operational Amplifier Circuit

Use all 10 kW resistors. Verify experimentally and using SPICE, the voltage gain at 1 kHz . Use both a time domain and transfer characteristic representation of your work. Frequency response measurements are not

Required Hint: The voltage gain should be -3 from your PRELAB derivation.

Some suggestions for writing laboratory reports although not part of our grading rubric.

For those of you who are “trekies” i.e. fans of the vintage Star Trek television series (50+ years old) and have a “smartphone”. By the way, NETFLIX has all of the original episodes which beats my pile of vintage VHS video cassettes I used to have of all the episodes. I also noted an article on CNN http://www.cnn.com/2014/09/03/tech/innovation/tricorder-x-prize-finalists/index.html that I thought was interesting. And the winner was https://www.nbcnews.com/mach/technology/these-er-docs-invented-real-star-trek-tricorder-n755631 An Apple Watch does a good job with heart rate and the FITBIT has all sorts of options.

My take on computer “customer service”. I feel so honored that my call is important to them as I listen to their so-called music.