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 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 2C 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) Rev A Copyright 2016 University of Saskatchewan Page 1 of 17

2 5. Material and Equipment Material (supplied by department) CD4007UB CMOS Dual Complementary Pair Plus Inverter Resistor: 100 Ω, 1 kω Equipment (supplied by student) Analog Discovery Waveforms software Breadboard and wiring kit Rev A Copyright 2016 University of Saskatchewan Page 2 of 17

3 6. Prelab 1. Download the datasheet for a MIC94050 from " What are the minimum and maximum Gate Threshold Voltages (I D = -250 µa)? 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 are the minimum and maximum Gate Threshold Voltages (I D = +250 µa)? 2.2. What is the value of I D with V DS = 3 V and V GS = 6 V? 3. A SPICE circuit file for the p-channel circuit Figure 7-8 is given in Figure 6-1. 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 Add trace "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 CMOSP ; MOSFET D G S B R1 d vss 100 ; 100 Ohm resistor Vss vss 0 ; Circuit source voltage Vgg g 0 ; Gate voltage ** Analysis Requests **.DC Vss 0V -5V -10mV Vgg 0V -4.75V -0.25V ************************************************** * Level 1 SPICE Models for the 4007 CMOS chip **************************************************.MODEL CMOSP PMOS ( LEVEL = 1 L=5u W=100u +VTO = KP = 3.2e-5 GAMMA = PHI = 0.65 LAMBDA = 9e-2 CBD = 65e-12 +CBS = 2e-14 IS = 1e-15 PB = CGSO = 0 CGDO = 0 CGBO = 1e-5 +CJ = 2e-10 MJ = 0.5 CJSW = 1e-9 +MJSW = 0.33 JS = 1e-8 TOX = 6.89e-10).end Figure 6-1: I D versus V DS (varying V GS) SPICE Circuit File Rev A Copyright 2016 University of Saskatchewan Page 3 of 17

4 Figure 6-2: Example SPICE Plot 4. The SPICE Model for an N-Channel MOSFET is shown in Figure 6-3. Create the SPICE Circuit File, and using LTspice, include a screen capture of the plot of the I D versus V DS characteristic in your lab report of the circuit in Figure 7-6. Remember you will have to adjust your voltages for the n-channel compared to the p-channel..model CMOSN NMOS ( LEVEL = 1 L=5u W=20u +VTO = 1.77 Kp = 2.169e-4 GAMMA = PHI = 0.65 LAMBDA = 1.5e-2 CBD = 20e-12 +CBS = 0 IS = 1e-15 PB = CBS = 2e-14 CGDO = 88e-8 CGBO = 0 +CJ = 2e-10 MJ = 0.5 CJSW = 1e-9 +MJSW = 0.33 JS = 1e-8 TOX = 1.265e-10) Figure 6-3: N-Channel MOSFET SPICE Model Rev A Copyright 2016 University of Saskatchewan Page 4 of 17

5 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). N-Channel MOSFET Threshold Voltage Change This experiment is to verify the effect of the voltage difference between the body (substrate) 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: Wavegen Channel 1 R D 1 kω 3 CD4007UB Wavegen Channel 2 Figure 7-1: I D versus V GS Circuit 2. Set Wavegen Channel 1 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 Wavegen Channel 2 to 10 steps from 0 V to V (in 0.25 V steps) in 0.1 second: 3.1. Create a text file with the numbers 1, 2,, 10, one on each line (make sure NOT to have any blank lines after the last number) Select the "Custom" waveform type. Rev A Copyright 2016 University of Saskatchewan Page 5 of 17

6 3.3. Then select "Import" and browse to the text file you created. "Open" to import the step waveform and press OK In the main Wavegen screen set Frequency = 10 Hz, Amplitude = V, and Offset = V Set to "Auto synchronization" which synchronizes Channels 1 and You may have to set the frequency of Channel 1 back to 100 Hz The Wavegen settings screen should look similar to Figure 7-2. Note how Channel 1 (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 Channel 2 (Vsb) Click "Run All" to start both channels. Figure 7-2: Wavegen Settings 4. Connect Channel 1 to measure V GS. 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. 6. Use the Scope to show the I D versus V GS: 6.1. Add Math 1 to calculate I D (i.e. "C2 / 1000"). Change the units of Math 1 to "A" and set the Range to something appropriate (e.g. 200 ua/div). Rev A Copyright 2016 University of Saskatchewan Page 6 of 17

7 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 trigger "Source" to "Wavegen 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 7-4) Obtain a screen capture/print out of the I D versus V GS graph and label the values of V SB on each curve. Figure 7-3: Scope Window Rev A Copyright 2016 University of Saskatchewan Page 7 of 17

8 Figure 7-4: I D versus V GS (multiple V SB) 6.6. Export the data from the "Main Time" window (see Figure 7-5). Export can be found under the File menu on the main Scope window. 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). Rev A Copyright 2016 University of Saskatchewan Page 8 of 17

9 Figure 7-5: Export Data Rev A Copyright 2016 University of Saskatchewan Page 9 of 17

10 N-Channel MOSFET I-V Characteristics 1. Construct the circuit shown Figure 7-6 on your breadboard: 1.1. Connect the body (substrate) to ground. Wavegen Channel 1 R D 100 Ω Wavegen Channel CD4007UB Figure 7-6: I D versus V DS Circuit 2. Set Wavegen Channel 1 to a 200 Hz Triangle wave, Amplitude = 2.5 V, Offset = 2.5 V, Phase = 270 degrees (should go from 0 V to +5 V). 3. Set Wavegen Channel 2 to 20 steps from 0 V to 4.75 V in 0.1 second: 3.1. Create a text file with the numbers 1, 2,, 20, one on each line Select the "Custom" waveform type Then select "Import" and browse to the text file you created. "Open" to import the step waveform and press OK Back in the main Wavegen screen, set Frequency = 10 Hz, Amplitude = V, and Offset = V Set "Auto synchronization" which synchronizes Wavegen Channels 1 and You may have to reset Channel 1 to 200 Hz The Wavegen screen should look similar to Figure 7-7. Note how Channel 1 (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 Channel 2 (V GS) Click "Run All" to start both channels. Rev A Copyright 2016 University of Saskatchewan Page 10 of 17

11 4. Connect Channel 1 to measure V DS. Figure 7-7: Wavegen Settings 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. 6. Use the Scope to show the I D versus V GS: 6.1. Add channel Math 1 (use Custom ) to calculate I D (i.e. "C2 / 100"). Change the units of Math 1 to "A" and set the Range to something appropriate (e.g. 1 ma/div) Set the trigger Source to Wavegen Turn off the display of Channel 2 and adjust the Time and Channel parameters to provide a good view of Channel 1 and Math 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 Scope Window and the I D versus V DS graph 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 A Copyright 2016 University of Saskatchewan Page 11 of 17

12 P-Channel MOSFET I-V Characteristics 1. Construct the circuit shown in Figure 7-8 on your breadboard: Wavegen Channel 1 R D 1 Wavegen 3 Channel 2 2 CD4007UB 100 Ω 14 Figure 7-8: I D versus V DS Circuit 2. Set Wavegen Channel 1 to a 200 Hz Triangle wave, Amplitude = 2.5 V, Offset = -2.5 V, Phase = 90 degrees (should go from 0 V to -5 V). 3. Set Wavegen Channel 2 to 20 steps from 0 V to V in 0.1 second: 3.1. Create a text file with the numbers 1, 2,, 20, one on each line Select the "Custom" waveform type Then select "Import" and browse to the text file you created. "Open" to import the step waveform and press OK Back in the main Wavegen screen, set Frequency = 10 Hz, Amplitude = V, and Offset = V Set "Auto synchronization" which synchronizes Wavegen Channels 1 and You may have to reset Channel 1 to 200 Hz The Wavegen screen should look similar to Figure 7-9. Note how Channel 1 (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 Channel 2 (V GS) Click "Run All" to start both channels. Rev A Copyright 2016 University of Saskatchewan Page 12 of 17

13 4. Connect Channel 1 to measure V DS. Figure 7-9: Wavegen Settings 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. 6. Use the Scope to show the I D versus V GS: 6.1. Add channel Math 1 (use Custom ) to calculate I D (i.e. "C2 / 100"). Change the units of Math 1 to "A" and set the Range to something appropriate (e.g. 1 ma/div) Set the trigger Source to Wavegen Turn off the display of Channel 2 and adjust the Time and Channel parameters to provide a good view of Channel 1 and Math 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 Scope Window and the I D versus V DS graph 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 A Copyright 2016 University of Saskatchewan Page 13 of 17

14 P-Channel MOSFET Threshold Voltage Change This experiment is to verify the effect of the voltage difference between the body (substrate) 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 7-10 on your breadboard: Wavegen Channel 1 R D 1 kω 3 CD4007UB Wavegen Channel 2 Figure 7-10: I D versus V GS Circuit 2. Set Wavegen Channel 1 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 Wavegen Channel 2 to 10 steps from 0 V to +4.5 V (in 0. 5 V steps) in 0.1 second: 3.1. Create a text file with the numbers 1, 2,, 10, one on each line (make sure NOT to have any blank lines after the last number) Select the "Custom" waveform type Then select "Import" and browse to the text file you created. "Open" to import the step waveform and press OK In the main Wavegen screen set Frequency = 10 Hz, Amplitude = 2.25 V, and Offset = 2.25 V Set to "Auto synchronization" which synchronizes Channels 1 and You may have to set the frequency of Channel 1 back to 100 Hz The Wavegen settings screen should look similar to Figure Note how Channel 1 (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 Channel 2 (Vsb) Click "Run All" to start both channels. Rev A Copyright 2016 University of Saskatchewan Page 14 of 17

15 4. Connect Channel 1 to measure V GS. Figure 7-11: Wavegen Settings 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. 6. Use the Scope to show the I D versus V GS: 6.1. Add Math 1 to calculate I D (i.e. "C2 / 1000"). Change the units of Math 1 to "A" and set the Range to something appropriate (e.g. 200 ua/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 trigger "Source" to "Wavegen 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 7-13) 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 A Copyright 2016 University of Saskatchewan Page 15 of 17

16 Figure 7-12: Scope Window 6.6. Export the data from the "Main Time" window (see Figure 7-14). Export can be found under the File menu on the main Scope window. 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). Rev A Copyright 2016 University of Saskatchewan Page 16 of 17

17 Figure 7-13: I D versus V GS (multiple V SB) Figure 7-14: Export Data Rev A Copyright 2016 University of Saskatchewan Page 17 of 17