EE 2212

Spring 2019

7 February 2019

Experiment 2: Frequency Domain Response for Passive Circuits and Operational Amplifier Circuits

Report Due: 14 February in Lab

Note 1: I will discuss the implementation of AC SPICE analysis in our lab introduction.

Note 2: I will provide an overview of the op amp SPICE models also at the beginning of the laboratory.

Note 3: Your frequency-independent designs will be used as the basis for the analog active LPF, HPF, and Band-Pass filter designs in Experiment 3, 14 February

Note 4: Because we missed lab last Thursday, snow day, I am combining elements of two lab experiments; consequently I am allowing up to five additional pages to accommodate graphs besides the cover sheet instead of three additional pages.

Note 5: EXCEL spread sheets are a good way to collect and display your data. EXCEL is resident on the lab computers and available through ITSS for your computers.

1. Construct the following two circuits on your prototype board. Observe that the circuits are duals of each other.

Frequency Domain Response Using Figure 1 (Low-Pass Filter)

You will now demonstrate analog filters. Filters, whether analog or digital, are very important components in most electronic systems

The circuit in Figure 1 is a basic single-pole analog, passive, low-pass filter (LPF). This LPF function can be observed by applying a constant-amplitude (i.e. 1volt peak amplitude input sinusoid and varying the frequency from 100 Hz to > 20 kHz.

Ø Measure, record and plot the voltage gain in dB and phase shift as a function of frequency (on a log scale). This is often called a Bode Plot. You may have seen similar plots for some of your audio equipment. Start at 100 Hz and end at a few tens of kHz. Measure the – 3 dB corner frequency of the filter, and the phase shift at that frequency. (Note that –3 dB corresponds to 70.7% of the low-frequency gain). Again, you can obtain phase directly from the oscilloscope “MEASURE” menu and visually verify by looking at the waveforms. Compare these measurements with theoretical and PSPICE values. Many of these measurements can be done by using soft key settings within the oscilloscope “MEASURE” menu.

Ø Compare your data to SPICE AC analysis plot.

FREQUENCY DOMAIN RESPONSE Of Figure 2 (High Pass Filter)

The circuit in Figure 2 is also a basic single-pole passive high-pass filter. To see this, observe the amplitude of the output as the frequency is varied from >20 kHz down to 100 Hz. You will need to use a 1 volt peak- amplitude input sinusoid.

Ø Measure, record and plot the voltage gain in dB and phase shift as a function of frequency (on a log scale). Start at a few tens of kHz and end at 100 Hz. Measure the – 3 dB corner frequency of the filter, and the phase shift at that frequency. (Note that –3 dB corresponds to 70.7% of the high-frequency gain). Again, you can obtain phase directly from the “MEASURE” menu and visually verify by looking at the waveforms. Compare these measurements with theoretical and PSPICE values. Many of these measurements can be done by using soft key settings within the oscilloscope “MEASURE” menu.

Ø Compare your data to SPICE AC analysis plot.

Ø Note that the -3dB frequency is the same for both the LPF and HPF since R and C are the same values.

3. To implement the designs of:

Ø An inverting operational amplifier, Figure 3

Ø A non-inverting operational amplifier, Figure 4

Note 1: 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

Ø 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.

Ø Specify the component values to meet the indicated specifications for Circuits 3 and 4 . 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. All resistor values must be 2 kΩ or larger for the μA741

PROCEDURE

Ø 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 in your design.

Ø 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.

Ø 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, and compare your results with the SPICE AC simulation. Extend your measurements to 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 3 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, 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 4 Non-Inverting Operational Amplifier Circuit

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 4 does a good job with heart rate and EKG, 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 elevator music.