Summer 2007 Lab 2EE100/EE43EECS 100/43Lab 2 – Function Generator and Oscilloscope1. ObjectiveIn this lab you learn how to use the oscilloscope and function generator2. Equipmenta. Breadboardb. Wire cuttersc. Wiresd. Oscilloscopee. Function Generatorf. 1k resistor x 2h. Various connectors (banana plugs-to-alligator clips) for connecting breadboardto power supply and for multimeter connections.3. Theorya. The HP33120A Function GeneratorThe front panel of your function generator is shown in Figure 1. This instrument outputsa time-varying periodic voltage signal (the OUTPUT connector, do not use the syncconnector, refer to figure 2). By pushing the appropriate buttons on the front panel, theuser can specify various characteristics of the signal.Figure 1. Front panel of your function generator(Ref: Agilent Function Generator User’s Guide #33120-90006)University of California, Berkeley Department of EECSSummer 2007 Lab 2EE100/EE43Figure 2. Make sure you use BLACK BNC input cables. Connect them to the OUTPUT terminal asshown above. Do not use the SYNC connectorThe main characteristics that you will be concerned with in this class are:- Shape: sine, square, or triangle waves.- Frequency: inverse of the period of the signal; units are cycles per second(Hz) - Vpp: peak to peak Voltage value of the signal- DC Offset: constant voltage added to the signal to increase or decrease itsmean or average level. In a schematic, this would be a DC voltage source inseries with the oscillating voltage source. Figure 3 below illustrates a couple of the parameters above.University of California, Berkeley Department of EECSSummer 2007 Lab 2EE100/EE43Figure 3. Sine wave Vpp and DC offsetWhen the function generator is turned on, it outputs a sine wave at 1 kHz with amplitude of 100 mVPP (figure 4).Figure 4. Function generator has been turned onYou must specify the characteristics of the signal you need. For example, to set thefrequency of the signal:1. Enable the frequency modify mode by pressing the Freq button. University of California, Berkeley Department of EECSSummer 2007 Lab 2EE100/EE432. Enter the value of the desired frequency by pressing the Enter Number button andentering the appropriate numbers on pads labeled with green numbers, or by using thewheel and the left and right arrows to move the tens place. (To cancel the number mode, press Shift and Cancel.) 3. Set the units to the desired value by using the arrow keys (up or down) on the right sideof the front panel. IMPORTANT NOTE: There is an internal resistor 50 ohms in series with the oscillatingvoltage source inside the function generator, refer to figure 5.Figure 5. The internal load resistor in your function generatorThus, if you connect the function generator to an external resistor RL, it will form avoltage divider with the 50 ohms resistor, refer to figure 6. University of California, Berkeley Department of EECSSummer 2007 Lab 2EE100/EE43Figure 6. External resistor forming a voltage dividerHence the voltage seen at the output of the instrument is:The purpose of the internal resistance is to have impedance matching (especiallyimportant for high frequency circuits). In RF electronics, resistances of 50 ohms arevery common. Therefore if RL = 50 ohm, we have:The front panel meter assumes RL = 50 ohms. As we saw above, a 50 ohm load leadsto a voltage divider with a gain of ½, so the instrument compensates for this by raising vintto twice what the display shows. In other words, if you set the instrument to produce a 5V sine wave, it actually produces a 10 V sine wave on vint and relies on the externalvoltage divider to reduce the signal by a factor of two. We are not going to change thedefault setting of this instrument, so just remember that you are getting twice thevoltage displayed on the function generator at the output terminal.That’s all for the function generator. Lets get to the crux of this lab – the oscilloscope.University of California, Berkeley Department of EECSSummer 2007 Lab 2EE100/EE43b. OscilloscopeNote: This section is mostly a paraphrase of [1]. It might also be useful to go through the Prelab as you read this section.Nature moves in the form of a sine wave, be it an ocean wave, earthquake, sonic boom,explosion, sound through air or the natural frequency of a body in motion. Even light –part particle, part wave – has a fundamental frequency which can be observed as color. Sensors can convert these forces into electrical signals that you can observe and studywith an oscilloscope. You will learn an example of a sensor – the Strain Gauge – in alater lab. For now, we will learn how to use an oscilloscope1.Oscilloscopes enable scientists, engineers, technicians, educators and others to “see”events that change over time. They are indispensable tools for anyone designing,manufacturing or repairing electronic equipment. Oscilloscopes are used by everyonefrom physicists to television repair technicians. An automotive engineer uses anoscilloscope to measure engine vibrations. A medical researcher uses an oscilloscope tomeasure brain waves. The possibilities are endless.i. Basic concepts behind an oscilloscopeWhat is an oscilloscope? An oscilloscope is basically a graph-displaying device – itdraws the graph of an electrical signal. In most applications, the graph shows howsignals change over time: the vertical (Y) axis represents voltage and the horizontal (X)axis represents time. The intensity or brightness of the signal is sometimes called the Z-axis (refer to figure 7).Figure 7. X, Y and Z components of a waveformThis simple graph can tell you many things about a signal such as:1 An oscilloscope takes sometime to get used to. Just remember a simple rule: oscilloscopes do notgenerate waveforms (except for a simple test signal), they measure waveforms.University of California, Berkeley Department of EECSSummer 2007 Lab 2EE100/EE43- The time and voltage values of a signal- The frequency of an oscillating signal- Whether or not a malfunctioning component is distorting the signal- How much of a signal is direct current (DC) or alternating current (AC)What kind of signals can you measure with an oscilloscope? Figure 8 shows somecommon signals (or waveforms).Figure 8. Common waveformsYou can measure different characteristics of a waveform with
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