LAB I. INTRODUCTION TO LAB EQUIPMENT

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1 LAB I. INTRODUCTION TO LAB EQUIPMENT 1. OBJECTIVE In this lab you will learn how to properly operate the basic bench equipment used for characterizing active devices: 1. Oscilloscope (Agilent MSO6032A), 2. Source Measure Unit (SMU) (Keithley 2430), 3. Function generator Agilent 33220A, and a 4. Bread board. You will use these tools to characterize three simple resistive circuits, perform theoretical circuit analyses on them, analyze the results, and present your findings in a concise, organized lab report. 2. OVERVIEW The Background Information section in this lab manual describes the basic operations of each lab equipment. You are expected to learn these basic operations during lab, ideally before moving on to the Lab Procedure section. The lab procedure will test your comprehension of the background materials by asking you to build simple resistive circuits and use the bench equipment to characterize them. Information essential to your understanding of this lab: 1. Background Material Materials necessary for this experiment: 1. Standard bench equipment. 2. Two resistors: 3.3 kω and 5.1 kω. 3. Two 10:1 Oscilloscope Probes. 4. One RG58C/U Coaxial Cable. 5. Two Red & Black Test Lead Pair (Banana-Plug to Alligator-Clip.) 3. BACKGROUND INFORMATION 3.1 BREADBOARD BASICS Breadboards (aka. Solderless board, Prototype board) are simply a set of pre-wired interconnected strips that are accessible through periodically spaced hole in the board. Looking at Figure 1., you can identify which holes form an interconnected strip by the black lines connecting them. By plugging the lead of a component into a hole you will be connected to all the other components in that strip without permanently connecting them. This allows you to build, alter, and test your prototype circuits quickly. Lab I: Introduction to Lab Equipment Page 1

2 There are two basic types of strips. The first type is called connection strip, they typically take up most of the board and are connected horizontally. Each hole can uniquely identified using the labels a-j column labels and 1-63 row labels. NOTE: a-e connection strips are not connected to the f-i connection strips. The second type is called bus strip. ALL the holes in a bus strip are connected vertically. Bus strips are typically labeled A or B and are marked by a red or blue line along their length. Figure 1. A schematic diagram of the breadboard showing buses and strips. 3.2 KEITHLEY SOURCE MEASURE UNIT 2400 The Keithley SMU can be used as a voltage source, a current source, a voltmeter, or an ammeter. Examine Figures 2. & 3. below before moving on to studying the main functions of the Keithley SMU. Figure 2. Keithley SMU button descriptions. Lab I: Introduction to Lab Equipment Page 2

3 Figure 3. Front panel of Keithley 2430 SMU SET VOLTAGE/CURRENT SOURCE CONFIGURATION In order to use the Keithley SMU as a voltage source or a current source, you need to follow the steps given below. 1. Press the V or I button in the Source group. 2. Press the EDIT button (top left): The display value V src or I src should start blinking. If it is not blinking press the EDIT button again. 3. To set your source value, you need to use the following buttons: Select Range: These buttons are used to change the range of the source value by an order of magnitude (i.e. by a factor of 10). Select Digit: The Left and Right arrows in the EDIT group are used to select the digit you wish to alter. Select Number: The Up and Down arrows in the source group are used to change the digit value. Lab I: Introduction to Lab Equipment Page 3

4 Or you can enter the numbers directly using these buttons: 4. Once you set the value, press Enter COMPLIANCE (IMPORTANT!!!) Once you have set your source value, you need to set your compliance value. How do I set the compliance value? Press the Edit button twice. You will see a set of digits blink. Use the same buttons you used to set your source value above to set your compliance value. How do I determine compliance value? Use data sheets to determine the voltage and current limits of your component. Next, use your magical powers of electrical engineering (also known as the mystical art of circuit analysis ) to figure what voltage and current your component will experience. For example the average resistor is rated at a ¼ watt. If you put 1V across that resistor, you need to make sure as a good and employable electrical engineer that you don t put more that 0.25A through it. Therefore, if you set up the SMU as a voltage source delivering 1V to your resistor, your compliance value will be 250mA. What is compliance? Compliance is a safety feature incorporated in the Keithley SMU to protect your circuit components from unexpected high power of operation i.e. it prevents you from unexpectedly frying your circuit. It is a limiting factor input by the user. If you set up an SMU as a voltage source, you must also set the highest current value the SMU is allowed to provide to your circuit; this is called current clamping. If you set up an SMU as a current source, you must set the highest voltage value the SMU is allowed to provide to your circuit; this is called voltage clamping. Lab I: Introduction to Lab Equipment Page 4

5 On the screen, the compliance value is typically displayed to the right of the source value, and in this format: Cmpl: ma (assuming you set up a voltage source.) Once you have set up source and compliance for an SMU, you can push the ON/OFF button at the bottom right corner of the front panel to power your circuit. Check the compliance value in the display. If something blinks, there is a problem. If you turn on your SMU and your circuit attempts to draw more current than is allowed by your compliance value, the Cmpl: text will blink (ex. Cmpl: ma ; here bold text indicates blinking text). This is called breaking real compliance. To overcome this, you need to increase the compliance value or recheck your circuit setup. If the units portion of your compliance value blinks ( Cmpl: ma ), you broke range compliance. It means the compliance value you entered is well above the range of current values being drawn by your circuit. The actual current drawn is below the range of measurement of the SMU. You need to press the AUTO button to allow the Keithley to set the compliance value to some lower value VOLTMETER / AMMETER CONFIGURATION To configure the Keithley SMU as an Ammeter or a Voltmeter, do the following: Voltmeter Setup: 1. Set the SMU up as a current source with zero output current. 2. Then from the control panel area, press the V button in the MEAS group under the display. Ammeter instructions 1. Set the SMU up as a voltage source with zero output voltage. 2. Then from the control panel area, press the I button in the MEAS group under the display. 3.3 AGILENT MSO6000 SERIES OSCILLOSCOPE This section will instruct you on how to operate the Agilent 6000 Series Oscilloscope. Lab I: Introduction to Lab Equipment Page 5

6 Figure 4. Front Panel of Agilent 6000 Series Oscilloscope OSCILLOSCOPE FRONT PANEL CONTROL Intensity Control (2 in Fig. 4) Rotate clockwise to increase the display intensity; counterclockwise to decrease. You can vary the intensity control to bring out signal detail, much like an analog oscilloscope. Digital channel waveform intensity is not adjustable. Autoscale Key (24 in Fig. 4) When you press the Autoscale key the oscilloscope will quickly determine which channels have activity, and it will turn these channels on and scale them to display the input signals. Vertical Position Control (6 in Fig. 4) Use this knob to change the channel s vertical position on the display. There is one Vertical Position control for each channel. Channel On/Off Key (7 in Fig. 4) Use this key to switch the channel on or off, or to access the channel s menu in the soft-keys. There is one Channel On/Off key for each channel. Vertical Sensitivity (9 in Fig. 4) Use this knob to change the vertical sensitivity (gain) of the channel. Lab I: Introduction to Lab Equipment Page 6

7 AutoProbe Interface (10 in Fig. 4) When you connect a probe to the oscilloscope, the AutoProbe Interface attempts to determine the type of probe and set its parameters in the Probe menu accordingly. Horizontal Delay Control (18 in Fig. 4) When the oscilloscope is RUNning, this control lets you set the acquisition window relative to the trigger point. When the oscilloscope is STOPped, you can turn this knob to pan through the data horizontally. This lets you see the captured waveform before the trigger (turn the knob clockwise) or after the trigger (turn the knob counterclockwise). Horizontal Sweep Speed Control (20 in Fig. 4) Turn this knob to adjust the sweep speed. This will change the time per horizontal division on the display. When adjusted after the waveform has been acquired and the oscilloscope is stopped, this has the effect of stretching out or squeezing the waveform horizontally. Measure Keys (21 in Fig. 4) Press the Cursors key to switch on cursors that you can use for making measurements. Press the Quick Meas key to access a set of predefined measurements Entry Knob (23 in Fig. 4) The entry knob is used to select items from menus and to change values. Its function changes based upon which menu is displayed. Note that the curved arrow symbol above the entry knob illuminates whenever the entry knob can be used to select a value. Use the entry knob to select among the choices that are shown on the softkeys. Softkeys (25 in Fig. 4) The functions of these keys change based upon the menus shown on the display directly above the keys. Probe Attenuation Factor: Some Oscilloscope probe attenuates the incoming signal by a certain factor. In this lab, we use 10:1 probe which attenuates the incoming signal by a factor of 10. By matching the attenuation factor of the oscilloscope to the attenuation of the probe, your measurements will reflect the actual voltage levels at the probe tip. Basic 10:1 probe calibration procedure: 1. Press the Save/Recall key on the front panel and then press the Default Setup Softkey (located directly below the display on the front panel). The oscilloscope is now configured to its default settings. 2. Select a probe and set the physical switch on the lead to 10x. 3. Connect the probe to channel 1, press the (1) button. 4. Ensure the resistance is set at 1Mohm on screen. 5. Press the softkey marked above Probe. Set the probe attenuation factor to 10:1. 6. Connect the oscilloscope probe to the Probe Comp signal terminal on the front panel. Lab I: Introduction to Lab Equipment Page 7

8 7. Connect the probe s ground lead to the ground terminal next to the Probe Comp terminal. 8. Press Autoscale. 9. You should see a waveform on the oscilloscope s display similar to this: 6. If the square wave form is not shaped correctly, it implies that the probes are not compensated to match to the oscilloscope s channels. In order to compensate the probe, you should adjust the trimmer capacitor of the probe (located on the probe BNC connector) for the flattest pulse possible using the plastic flathead driver provided with the probe MEASURING VOLTAGES AND TIME-RELATED PARAMETERS When measuring voltages with the oscilloscope, place the probes in parallel across the component where the voltage signal is being measured. Once you have the signal displayed on the screen, you can use buttons and keys to do the measurements. To measure RMS, DC, or peak to peak voltages with the oscilloscope, use the following method: Press the Quick Meas button on the Measure keys section (21 in Fig. 4). The Select menu appears on the bottom of the screen. Press the button beneath that, or use the Entry Knob (23 in Fig. 3) to select the desired value like RMS, Amplitude, Average, Peak to peak etc. The selected value would be displayed on the bottom of the display. To measure Frequency, period and other time-related parameters with the oscilloscope, use the following method: Press the Quick Meas button on the Measure keys section (21 in Fig. 4). The Select menu appears on the bottom of the screen. Press the button beneath that, or use the Entry Knob (23 in Fig. 3) to select the desired value Frequency, delay, period, Duty cycle etc. The selected value would be displayed on the bottom of the display. For other measurements related to the voltage and time-related parameters, we use cursors. To measure using the cursors do the following: Cursors are horizontal and vertical markers that indicate X-axis Lab I: Introduction to Lab Equipment Page 8

9 values (usually time) and Y-axis values (usually voltage) on a selected waveform source. The position of the cursors can be moved turning the Entry knob. When you press the Cursors key, it will illuminate and the cursors will turn on. To turn cursors off, press this key again until it is not illuminated, or press the Quick Meas key. Cursors are not always limited to the visible display. If you set a cursor, then pan and zoom the waveform until the cursor is off screen, its value will not be changed, and if you pan the waveform back again it will have the cursor in the original place. The following steps guide you through the front-panel Cursors key. You can use the cursors to make custom voltage or time measurements on the signal. 1. Connect a signal to the oscilloscope and obtain a stable display. 2. Press the Cursors key. View the cursor functions in the softkey menu: Mode Sets the cursors to measure voltage and time (Normal), or displays the binary or hexadecimal logic value of the displayed waveforms. Source Selects a channel or math function for the cursor measurements. X Y Selects either the X cursors or the Y cursors for adjustment with the Entry knob. X1 and X2 Adjust horizontally and normally measure time. Y1 and Y2 Adjust vertically and normally measure voltage. X1 X2 and Y1 Y2 Move the cursors together when turning the Entry knob. Lab I: Introduction to Lab Equipment Page 9

10 Cursor Examples 1. Cursors measure pulse widths other than middle threshold points 2. Cursors measure frequency of pulse ringing MEASURING CURRENTS The Oscilloscope can only measure current indirectly, by reading the voltage across a resistor while it is in a circuit and then applying Ohm s Law to find the current. If you have two signals and want to find the phase between similar points select the source of measurement for cursor 1 as channel 1 and the source for cursor 2 as channel 2. The difference readout is the delay between the two signals. If you divide that delay by the period then you have the phase value as a fraction of 360, or 2π radians. If you would like to represent that in degrees all you have to do is convert it from radians to degrees. Lab I: Introduction to Lab Equipment Page 10

11 3.4. FUNCTION GENERATOR AGILENT 33220A The function generator is used to generate signals for your circuits. You will need to know how to set the function generator to get sine, square, triangle or ramp signals. In addition, you will have to set up the frequency, the amplitude, offset voltage and the duty cycle. The default settings for this instrument are a sinewave of 1 khz, with an amplitude of 100 mv and a DC offset of 0.0 V. Figure 5. Front panel of the Agilent 33220A function generator. The function generator is very easy to use since each function has a specific button. If you want to select a waveform, just look for the button with the desired waveform such as a sine wave, a square wave, triangle wave, or ramp wave. Then, just press its button. All that you have to do now is set the parameters for the waveform. To set the frequency, amplitude, offset or the duty cycle you need to do the following: 1. Press the appropriate gray buttons beneath the display screen (Freq/Period, Ampl/Hi Level, Offset/Lo Level, or Duty Cycle). 2. You may enter the value one of two ways. a.) Turn the knob and the highlighted digit will change. You may select a different digit by using the < or the > buttons. b.) You can also key in the digit by using number buttons. 3. Press Output button on the bottom right of the front panel (right next to Sync cable) and make sure the light is on. Lab I: Introduction to Lab Equipment Page 11

12 IMPEDANCE MATCHING (IMPORTANT!) In order to make sure you read the exact value of the amplitude output by the function generator, You should make sure the output impedance of the function generator is matched to the impedance of the connected circuits. This function generator has 50 Ω output impedance. It has been configured by the manufacturer to deliver the voltage signal when a load of 50 Ω is attached to it. In the case of large impedance circuits the function generator may deliver up to twice the voltage that you have set it up to deliver. In our case, we use a series connected 5.1 kω resistor and 3.3 k Ω resistor, which is much higher than 50 Ω. Hence, when you set 1 V pp on the function generator, you will observe twice the amplitude (2 V pp ) on the oscilloscope. In order to overcome this, you need to set the function generator to have High Z output impedance. To do this, press the Utility button and press the output setup and you can change the output impedance to the High Z output mode. 4. PREPARATION There is no preparation for this lab except for reading and learning the background material. 5. PROCEDURE Before proceeding with the lab, please familiarize yourself with setting up the bench equipment. Refer to Section 3 for details. 5.1 FUNCTION GENERATOR AND OSCILLOSCOPE Use the function generator and the oscilloscope to perform the following tasks. 1. Build circuit A shown below in Figure Set the function generator to generate a sinusoidal signal with a frequency of 100 Hz and peak-to-peak voltage of 5V. 3. Set up one probe across the whole circuit, and another across R2. 4. Subtract Channel 2 signals from Channel 1 signals using the Oscilloscope. 5. Measure the voltages and time related parameters asked for on the Instructor Verification Sheet. Obtain TA Signature. Lab I: Introduction to Lab Equipment Page 12

13 Figure 6. Circuit A 5.2 KEITHLEY SMU Use the two Keithley SMUs to perform the following tasks: Using the circuit B of Figure 7 set up a Keithley SMU as a voltage source of 10 V DC. Figure out the compliance by evaluating the circuit. Use the second Keithley SMU to measure the voltages in R1 and R2. Measure the current in the circuit directly from the Keithley SMU used as the voltage source. Record values on IV sheet Using the circuit C of Figure 8, set up a Keithley SMU as a current source of 5 ma DC. Set up the other Keithley to measure the current in R1 and in R2. Record Values on IV Sheet Measure the impedance of your two resistors using the Ohmmeter setting of a Keithley SMU. Record the values in the Instructor Verification Sheet. Get TA Signature. Figure 7. Circuit 'B' Figure 8. Circuit 'C' Lab I: Introduction to Lab Equipment Page 13

14 Notice that Circuits B and C are source transforms of each other. You should be able to compare and contrast the voltage and current measurements. 6. LAB REPORT Type a lab report with a cover sheet containing your name, class (including section number), date of the lab, and the report due date. Use the following outline to draft sections of your lab report: Abstract: Briefly describe the purpose of the lab, the analysis you performed, and your findings. Introduction: Briefly mention the bench equipment you used in the lab and their basic functions in your own words. Procedure: You do not need to provide a procedure section for this lab. Data Presentation: Report all the measured data collected. Make sure it is well presented, has units and labels - and is easily discernable which values are from a particular section of the procedure. Please use Excel, Matlab or another software to help generate well-formed tables. Analysis: Perform theoretical circuit analysis on each circuit you characterized i.e. use the measured values of your resistors (5.2.3) to find the theoretical voltage and current values for circuit A, B, and C. Do show work typed equations, units etc. Include the circuit diagrams in your descriptions, if needed. Compare your calculated values to the measured values using percent error calculations. Be sure to organize your analyses appropriately according to procedure section number. Conclusions: What conclusions can you draw about using bench equipment from your direct experience of setting it up and using it to characterize circuits? What do the results of your circuit analyses tell you about your bench equipment? Lab I: Introduction to Lab Equipment Page 14