Lab 5: MOSFET I-V Characteristics

Transcription

1 1. Learning Outcomes Lab 5: MOSFET I-V Characteristics In this lab, students will determine the MOSFET I-V characteristics of both a P-Channel MOSFET and an N- Channel MOSFET. Also examined is the effect of the Source-Body voltage on the threshold voltage of a MOSFET. The Analog Discovery Kit will be used the main equipment in this experiment. 2. Health and Safety Any laboratory environment may contain conditions that are potentially hazardous to a person s health if not handled appropriately. The Electrical Engineering laboratories obviously have electrical potentials that may be lethal and must be treated with respect. In addition, there are also mechanical hazards, particularly when dealing with rotating machines, and chemical hazards because of the materials used in various components. Our LEARNING OUTCOME is to educate all laboratory users to be able to handle laboratory materials and situations safely and thereby ensure a safe and healthy experience for all. Watch for posted information in and around the laboratories, and on the class web site. 3. Lab Report Students work in groups of 2 with laboratories being on alternative week (in 2C80/82). Each student must have a lab book for the labs. The lab book is used for lab preparation, notes, record, and lab reports. The lab books must be handed before 5:00 pm on the due date (same day of the following week) into the box labeled for your section across from 2C94. The lab books are marked and returned before the next lab. 4. Background The MOSFET is actually a four-terminal device, whose substrate, or body, terminal must be always held at one of the extreme voltage in the circuit, either the most positive for the PMOS or the most negative for the NMOS. One unique property of the MOSFET is that the gate draws no measurable current. Another is that either polarity of voltage maybe applied to the gate without causing damage to the transistor. Although enhancement-mode MOSFETs respond to only one polarity, the students need not fear the consequences of using the opposite polarity. A MOSFET with its gate and drain connected together always operates in the constant-current region. Its I D to V GS relationship is: ( ) I = K V V (1) D GS TR where the threshold voltage depends on the source-body potential V SB as: VTR = VTR 0 ± γ 2φF + VSB 2φ F (2) 0.5 Using the typical values γ = 0.4 V and φ F = 0.3 V gives the following values for the change in threshold voltage of an nmos transistor. Rev B Copyright 2015 University of Saskatchewan Page 1 of 14

2 V SB (V) V TR-V TR Material and Equipment Material (supplied by department) MIC94050 P-Channel MOSFET Resistor: 560 Ω IRFD110 N-Channel MOSFET Equipment (supplied by student) Analog Discovery Module Waveforms software Breadboard and wiring kit Rev B Copyright 2015 University of Saskatchewan Page 2 of 14

3 6. Prelab 1. Download the datasheet for a MIC94050 from " What is the Gate Threshold Voltage? 1.2. What is the value of I D with V DS = 2 V and V GS = 2 V? 2. Download the datasheet for an IRFD110 from " What is the Gate Threshold Voltage? 2.2. What is the value of I D with V DS = 0.5 V and V GS = 4.5 V? 3. A SPICE circuit file for the MIC94050 circuit (Figure 7-1) is given in Figure 6-1. Using LTspice (a guide to using LTspice can be found in Laboratory #1 Appendix A), include a screen capture of the plot of the I D versus V GS characteristic in your lab report The horizontal axis should be set to "V(gs)". To set the horizontal axis, mouse over any of the numbers listed in the horizontal axis and "click" to bring up the "Horizontal Axis" dialog The vertical axis should be set to "Id(M1)" (using "Plot Settings Add Trace") The plot should look similar to Figure 6-2. P-Channel MOSFET I_d versus V_gs for varying V_sb ** Circuit Description ** M1 gs gs 0 body PMOSFET R1 gs vss 560 Vss vss 0 Vbb body 0 ; MOSFET D G S B ; 560 Ohm resistor ; Circuit source voltage ; Body voltage ** Analysis Requests **.DC Vss 0V -5V -100mV Vbb 0V 4V 1V ** Models **.MODEL PMOSFET PMOS (KP=0.4 VTO=-0.9 GAMMA=0.4 PHI=0.6 LAMBDA=0.5).end Figure 6-1: I D versus V GS (varying V SB) SPICE Circuit File Rev B Copyright 2015 University of Saskatchewan Page 3 of 14

4 Figure 6-2: Example SPICE Plot 4. A SPICE circuit file for the MIC94050 circuit (Figure 7-7) is given in Figure 6-3. Using LTspice, include a screen capture of the plot of the I D versus V GS characteristic in your lab report The horizontal axis should be set to "V(d)". To set the horizontal axis, mouse over any of the numbers listed in the horizontal axis and "click" to bring up the "Horizontal Axis" dialog The vertical axis should be set to "Id(M1)" (using "Plot Settings Add Trace") The plot should look similar to Figure 6-4. P-Channel MOSFET I_d versus V_ds for varying V_gs ** Circuit Description ** M1 d g 0 0 PMOSFET ; MOSFET D G S B R1 d vss 560 ; 560 Ohm resistor Vss vss 0 ; Circuit source voltage Vgg g 0 ; Gate voltage ** Analysis Requests **.DC Vss 0V -5V -100mV Vgg -0.8V ** Models **.MODEL PMOSFET PMOS (KP=0.4 VTO=-0.9 GAMMA=0.4 PHI=0.6 LAMBDA=0.5).end Figure 6-3: I D versus V DS (varying V GS) SPICE Circuit File Rev B Copyright 2015 University of Saskatchewan Page 4 of 14

5 Figure 6-4: Example SPICE Plot 5. The SPICE Model for an N-Channel MOSFET is shown in Figure 6-5. Create the SPICE Circuit File, and using LTspice, include a screen capture of the plot of the I D versus V GS characteristic in your lab report of the circuit in Figure MODEL NMOSFET NMOS (KP=0.05 VTO=2.7 LAMBDA=0.05) Figure 6-5: N-Channel MOSFET SPICE Model Rev B Copyright 2015 University of Saskatchewan Page 5 of 14

6 7. Lab Procedures Debugging (or What To Try When Things Aren't Working) There are a number of things/procedures you should use to debugging circuits when things are not working correctly. These include (but are not limited to): Check that all component pins are correctly inserted in the breadboard (sometimes they get bent underneath a component). Make sure that components are not "misaligned" in the breadboard (e.g. off by one row). Double check component values (you can measure resistors, capacitors, and inductors). Try a different section in the breadboard (in case there is a bad internal connection). Measure the source voltages to verify power input. Measure key points in the circuit for proper voltage/waveform (i.e. divide-and-conquer). Threshold Voltage Change Due to Source-To-Body (Substrate) Voltage This experiment is to verify the effect of the voltage difference between the body (bulk) and the source on the threshold voltage as shown in the text book (equation 5.30, 7th edition, equation 5.107, 6th edition). 1. Construct the circuit shown in Figure 7-1 on your breadboard: 1.1. The "pin out" for a MIC94050 p-channel MOSFET is shown in Figure 7-2. The MIC94050 is a "surface mount" component and so must be attached to a daughter board to be usable in a breadboard. There are two different types of daughter boards as shown in the figure. The "Black Mark" on the second one indicates the B (Body/Substrate) connection. MIC94050 G S B (Substate) To AWG2 D R D 560 Ω To AWG1 Figure 7-1: I D versus V GS Circuit 2. Set Arbitrary Waveform Generator AWG1 to a 100 Hz Triangle wave, Amplitude = 2.5 V, Offset = -2.5 V, Phase = 90 degrees (should go from 0 V to -5 V). Rev B Copyright 2015 University of Saskatchewan Page 6 of 14

7 B (Body) D B Black Mark G S B D G S Figure 7-2: MIC94050 Pin Outs 3. Set Arbitrary Waveform Generator AWG2 to 5 steps from 0 V to 4 V (in 1 V steps) in 1 second: 3.1. Create a text file with the numbers 1, 2,, 5, one on each line (make sure to have a blank line after the last number) Select the "Custom" waveform type Then select "File" and "Browse" to the text file you created. "Open" to create the step waveform Set Frequency = 1 Hz, Amplitude = 2 V, and Offset = 2 V Set "Mode" to "Auto sync" which synchronizes AWG1 and AWG The AWG settings screen should look similar to Figure 7-3. Note how AWG1 (the voltage across the resistor and MOSFET) varies from 0 V to -5 V and then back to 0 V for each voltage step in AWG2 (Vsb) Click "Run All" to start both AWGs. 4. Connect Channel 1 to measure V GS (i.e. 1+ on "G" and 1- on "S"). 5. Connect Channel 2 to measure the voltage across Resistor R D. We will use this voltage to determine the current I D into the MOSFET (i.e. 2+ on "AWG1" and 2- on "D"). 6. Use the ADM Oscilloscope to show the I D versus V GS: 6.1. Add Math 1 to calculate I D (i.e. "C2 / 560"). Change the units of Math 1 to "A" and set the Range to something appropriate (e.g. 1 ma/div) Turn off the display of Channel 2 and adjust the Time and Channel parameters to provide a good view of Channel 1 and Math 1. Set the "Source" to "AWG 2" and if you select the "Single" capture, you should see something similar to Figure Use "Add XY" to display the I D versus V GS graph (X = Channel 1 and Y = Math 1) Further adjust the parameters for Channel 1 and Math 1 to provide a good view of the I D versus V GS graph (similar to Figure 7-5) Obtain a screen capture/print out of the I D versus V GS graph and label the values of V SB on each curve. Rev B Copyright 2015 University of Saskatchewan Page 7 of 14

8 Figure 7-3: AWG Settings Figure 7-4: Oscilloscope Window Rev B Copyright 2015 University of Saskatchewan Page 8 of 14

9 Figure 7-5: I D versus V GS (multiple V SB) 6.6. Export the data from the "Main Time" window (see Figure 7-6). Use your favourite software to plot the linear region of II DD versus VV GGGG for each different value of VV SSSS. The slope of each curve is KK. Determine the value of KK in mmmm VV 2. Extrapolate each curve to II DD=0 to give the threshold voltage, VV TTTT. Using your measurements, find VV TTTT0 (i.e. threshold voltage when VV SSSS = 0 VV). Figure 7-6: Export Data Rev B Copyright 2015 University of Saskatchewan Page 9 of 14

10 P-Channel MOSFET I-V Characteristics 1. Construct the circuit shown in Figure 7-7 on your breadboard: 1.1. The "pin out" for a MIC94050 p-channel MOSFET is shown in Figure 7-2. To AWG2 MIC94050 G S B (Substate) D R D 560 Ω To AWG1 Figure 7-7: I D versus V DS Circuit 2. Set Arbitrary Waveform Generator AWG1 to a 100 Hz Triangle wave, Amplitude = 2.5 V, Offset = -2.5 V, Phase = 90 degrees (should go from 0 V to -5 V). 3. Set Arbitrary Waveform Generator AWG2 to 10 steps from -0.8 V to -1.1 V in 0.1 second: 3.1. Create a text file with the numbers 1, 2,, 10, one on each line (make sure to have a blank line after the last number) Select the "Custom" waveform type Then select "File" and "Browse" to the text file you created. "Open" to create the step waveform Set Frequency = 10 Hz, Amplitude = 150 mv, and Offset = -950 mv Set "Mode" to "Auto sync" which synchronizes AWG1 and AWG The AWG settings screen should look similar to Figure 7-8. Note how AWG1 (the voltage across the resistor and MOSFET) varies from 0 V to -5 V and then back to 0 V for each voltage step in AWG2 (V GS) Click "Run All" to start both AWGs. 4. Connect Channel 1 to measure V DS (i.e. 1+ on "D" and 1- on "S"). 5. Connect Channel 2 to measure the voltage across Resistor R D. We will use this voltage to determine the current I D into the MOSFET (i.e. 2+ on "AWG1" and 2- on "D"). 6. Use the ADM Oscilloscope to show the I D versus V GS: 6.1. Add Math 1 to calculate I D (i.e. "C2 / 560"). Change the units of Math 1 to "A" and set the Range to something appropriate (e.g. 1 ma/div). Rev B Copyright 2015 University of Saskatchewan Page 10 of 14

11 Figure 7-8: AWG Settings 6.2. Turn off the display of Channel 2 and adjust the Time and Channel parameters to provide a good view of Channel 1 and Math 1. Set the "Source" to "AWG 2" and if you select the "Single" capture, you should see something similar to Figure Use "Add XY" to display the I D versus V DS graph (X = Channel 1 and Y = Math 1) Further adjust the parameters for Channel 1 and Math 1 to provide a good view of the I D versus V DS graph (similar to Figure 7-10) REQUIRED: Demonstrate the Oscilloscope Window from 6.2 and the I D versus V DS graph from 6.4 to a lab instructor and make sure your demonstration is recorded by the lab instructor. 7. Obtain a screen capture/print out of the I D versus V DS graph and label the values of V GS on each curve. 8. Determine the average power dissipated in the transistor: 8.1. Add Math 2 to display the power in the transistor, PP = VV DDDD II DD (i.e. ( C2 / 560 ) * C1 ) Add a Measurement for the Average of Math 2. Rev B Copyright 2015 University of Saskatchewan Page 11 of 14

12 Figure 7-9: Oscilloscope Window Figure 7-10: I D versus V DS Rev B Copyright 2015 University of Saskatchewan Page 12 of 14

13 N-Channel MOSFET I-V Characteristics 1. Construct the circuit shown Figure 7-11 on your breadboard: 1.1. The "pin out" for an IRFD110 N-Channel MOSFET is shown in Figure To AWG1 R D 560 Ω To AWG2 G D S IRFD110 Figure 7-11: I D versus V DS Circuit Figure 7-12: IRFD110 Pin Out 2. Set Arbitrary Waveform Generator AWG1 to a 100 Hz Triangle wave, Amplitude = 2.5 V, Offset = 2.5 V, Phase = 270 degrees (should go from 0 V to +5 V). 3. Set Arbitrary Waveform Generator AWG2 to 10 steps from 2.7 V to 3.2 V in 0.1 second: 3.1. Create a text file with the numbers 1, 2,, 10, one on each line (make sure to have a blank line after the last number) Select the "Custom" waveform type Then select "File" and "Browse" to the text file you created. "Open" to create the step waveform Set Frequency = 10 Hz, Amplitude = 250 mv, and Offset = 2.95 V Set "Mode" to "Auto sync" which synchronizes AWG1 and AWG2. Rev B Copyright 2015 University of Saskatchewan Page 13 of 14

14 3.6. The AWG settings screen should look similar to Figure Note how AWG1 (the voltage across the resistor and MOSFET) varies from 0 V to +5 V and then back to 0 V for each voltage step in AWG2 (V GS) Click "Run All" to start both AWGs. Figure 7-13: AWG Settings 4. Connect Channel 1 to measure V DS (i.e. 1+ on "D" and 1- on "S"). 5. Connect Channel 2 to measure the voltage across Resistor R D. We will use this voltage to determine the current I D into the MOSFET (i.e. 2+ on "AWG1" and 2- on "D"). 6. Use the ADM Oscilloscope to show the I D versus V GS: 6.1. Add Math 1 to calculate I D (i.e. "C2 / 560"). Change the units of Math 1 to "A" and set the Range to something appropriate (e.g. 1 ma/div) Turn off the display of Channel 2 and adjust the Time and Channel parameters to provide a good view of Channel 1 and Math 1. Set the "Source" to "AWG 2" and if you select the "Single" capture Use "Add XY" to display the I D versus V DS graph (X = Channel 1 and Y = Math 1) Further adjust the parameters for Channel 1 and Math 1 to provide a good view of the I D versus V DS graph REQUIRED: Demonstrate the Oscilloscope Window from 6.2 and the I D versus V DS graph from 6.4 to a lab instructor and make sure your demonstration is recorded by the lab instructor Obtain a screen capture/print out of the I D versus V DS graph and label the values of V GS on each curve. Rev B Copyright 2015 University of Saskatchewan Page 14 of 14