Summer 2007 EE100 EE43 Lab 2 EECS 100 43 Lab 2 Function Generator and Oscilloscope 1 Objective In this lab you learn how to use the oscilloscope and function generator 2 Equipment a Breadboard b Wire cutters c Wires d Oscilloscope e Function Generator f 1k resistor x 2 h Various connectors banana plugs to alligator clips for connecting breadboard to power supply and for multimeter connections 3 Theory a The HP33120A Function Generator The front panel of your function generator is shown in Figure 1 This instrument outputs a time varying periodic voltage signal the OUTPUT connector do not use the sync connector refer to figure 2 By pushing the appropriate buttons on the front panel the user 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 EECS Summer 2007 EE100 EE43 Lab 2 Figure 2 Make sure you use BLACK BNC input cables Connect them to the OUTPUT terminal as shown above Do not use the SYNC connector The 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 its mean or average level In a schematic this would be a DC voltage source in series with the oscillating voltage source Figure 3 below illustrates a couple of the parameters above University of California Berkeley Department of EECS Summer 2007 EE100 EE43 Lab 2 Figure 3 Sine wave Vpp and DC offset When the function generator is turned on it outputs a sine wave at 1 kHz with amplitude of 100 mV figure 4 PP Figure 4 Function generator has been turned on You must specify the characteristics of the signal you need For example to set the frequency of the signal 1 Enable the frequency modify mode by pressing the Freq button University of California Berkeley Department of EECS Summer 2007 EE100 EE43 Lab 2 2 Enter the value of the desired frequency by pressing the Enter Number button and entering the appropriate numbers on pads labeled with green numbers or by using the wheel 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 side of the front panel IMPORTANT NOTE There is an internal resistor 50 ohms in series with the oscillating voltage source inside the function generator refer to figure 5 Figure 5 The internal load resistor in your function generator Thus if you connect the function generator to an external resistor R it will form a L voltage divider with the 50 ohms resistor refer to figure 6 University of California Berkeley Department of EECS Summer 2007 EE100 EE43 Lab 2 Figure 6 External resistor forming a voltage divider Hence the voltage seen at the output of the instrument is The purpose of the internal resistance is to have impedance matching especially important for high frequency circuits In RF electronics resistances of 50 ohms are very common Therefore if RL 50 ohm we have The front panel meter assumes R 50 ohms As we saw above a 50 ohm load leads L to a voltage divider with a gain of so the instrument compensates for this by raising vint to twice what the display shows In other words if you set the instrument to produce a 5 V sine wave it actually produces a 10 V sine wave on vint and relies on the external voltage divider to reduce the signal by a factor of two We are not going to change the default setting of this instrument so just remember that you are getting twice the voltage 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 EECS Summer 2007 EE100 EE43 Lab 2 b Oscilloscope Note 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 study with an oscilloscope You will learn an example of a sensor the Strain Gauge in a later 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 everyone from physicists to television repair technicians An automotive engineer uses an oscilloscope to measure engine vibrations A medical researcher uses an oscilloscope to measure brain waves The possibilities are endless i Basic concepts behind an oscilloscope What is an oscilloscope An oscilloscope is basically a graph displaying device it draws the graph of an electrical signal In most applications the graph shows how signals 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 Zaxis refer to figure 7 Figure 7 X Y and Z components of a waveform 1 An oscilloscope takes sometime to get used to Just remember a simple rule oscilloscopes do not generate waveforms except for a simple test signal they measure waveforms University of California Berkeley Department of EECS Summer 2007 EE100 EE43 Lab 2 This simple graph can tell you many things about a signal such as 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 some common signals or waveforms Figure 8 Common waveforms You can measure different characteristics of a waveform with an oscilloscope amplitude frequency DC offset and phase University of California Berkeley Department of EECS Summer 2007 EE100 EE43 Lab 2 Figure 9 Degrees of a sine wave Figure 10 Concept of Phase shift Phase is best explained by looking at sine waves figure 9 The voltage level of sine
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