Lab 6 - NMOS

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ELEE 3101 Electronics I Lab Lab 6: Basic MOSFET Measurements & SPICE Model Files Page 1 of 4 Lab 6: Basic MOSFET Measurements & SPICE Model Files Student name: ________________________________ Student ID: ____________ I. Introduction In this lab you will characterize the MOSFET in two ways. In the first set of measurements, 𝑉 𝐷? will be at a fixed value designed to put the device in the saturation region, and 𝐼 𝐷 will be measured as 𝑉 𝐺? is varied. The MOSFET should approximately follow the parabolic saturation equation (Square Law). II. Objectives • Extract 𝑘 𝑛 and 𝑉 𝑡ℎ via measurements. • Introduction to SPICE models. III. Equipment Required • Digital Multimeter • Breadboard • Miscellaneous cables IV. Material Required • 1 MOSFET IRF540 (N-Channel MOSFET) • 1 Resistors of 100 Ω • 1 Potentiometer of 5 kΩ or 10 kΩ • Jumper wires

ELEE 3101 Electronics I Lab Lab 6: Basic MOSFET Measurements & SPICE Model Files Page 2 of 4 V. Before the Lab 1. Read the “IN THE LAB” section in its entirety. 2. Download the datasheets for the IRF540 and fill in Table 1 Table 1.- MOSFET Maximum Ratings Part Number Max Current ( 𝐼 ) Max 𝑉 𝐷? Max Power Dissipation Threshold Voltage VI. In the Lab WARNING: You should set the maximum current limits to you power supply to 100 mA . NOTE: Do not turn on the 𝑉 𝐷𝐷 supply until you have read Steps (1)- (3), you are sure the circuit is correct, and you are sure that the gate voltage has been set to zero. Otherwise, you may burn out the MOSFET. 6.1 𝑰 𝑫 versus 𝑽 𝑮𝑺 , for fixed 𝑽 𝑫𝑺 Figure 1.- MOSFET circuit schematic 1. Measure and record the actual value of the 100 Ω source resistance 𝑅 ? and verify you have correctly set the power supply limit to 100 mA . 2. Construct the circuit in Figure 1 and adjust the potentiometer so that 𝑉 𝐺? = 0 V . 3. Using Excel or similar SW, build a table with the following columns: 𝑉 𝐺 , 𝑉 ? , 𝑉 𝐺? , 𝐼 𝐷 and (𝐼 𝐷 ) 0.5 . Add formulas into your spreadsheet so that it uses the measured value of 𝑅 ? , 𝑉 𝐺 and 𝑉 ? to automatically calculate 𝑉 𝐺? , 𝐼 𝐷 (using Ohm’s Law) and (𝐼 𝐷 ) 0.5 .

ELEE 3101 Electronics I Lab Lab 6: Basic MOSFET Measurements & SPICE Model Files Page 3 of 4 4. Adjust the potentiometer to increase 𝑉 𝐺 in steps of approximately 0.2 V . At each step record 𝑉 𝐺 and 𝑉 ? . Keep in mind that you will not see significant current ( > 0.1 mA ) until 𝑉 𝐺? exceeds the threshold voltage. You may increase the increments, to half a volt after you’ve reached a drain current of 20 mA . 5. Plot 𝐼 𝐷 versus 𝑉 𝐺? . 6. Plot √𝐼 𝐷 versus 𝑉 𝐺? . For this second plot, you should omit the measurements in which 𝐼 𝐷 (not √𝐼 𝐷 ) is less than 5 mA . MOSFETs do not accurately follow the square law when the gate when operating in or near the subthreshold regime. 7. Calculate the value of 𝑘 𝑛 and 𝑉 ?ℎ using the √𝐼 𝐷 versus 𝑉 𝐺? plot. 6.2 𝑰 𝑫 versus 𝑽 𝑫𝑺 , for fixed 𝑽 𝑮𝑺 Figure 2.- 𝑉 𝐺? fixed circuit schematic. 1. Using a IRF540, build the circuit in Figure 2. Set 𝑉 𝐷𝐷 to 10 V (saturation region) and adjust the potentiometer to set 𝑉 𝐺? such that 𝐼 𝐷 is approximately 20 mA and record this value of 𝑉 𝐺? and calculate the 𝑉 𝑂𝑉 . 2. Set 𝑉 𝐷𝐷 to 0 V (triode region). Then increase 𝑉 𝐷𝐷 in 50 mV steps (if possible) until the MOSFET enters saturation ( 𝑉 𝑂𝑉 = 𝑉 𝐷? ), recording 𝑉 𝐷? and 𝐼 𝐷 at each step. You will know when the MOSFET enters saturation because the current will plateau. Once the saturation regime has been reached, you may increase your steps to 0.5 Volts. Continue until you reach 𝑉 𝐷? = 10 V . 3. Make a plot of 𝐼 𝐷 versus 𝑉 𝐷? using the data captured in steps 1-2 of Part II and take additional data points as needed.

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ELEE 3101 Electronics I Lab Lab 6: Basic MOSFET Measurements & SPICE Model Files Page 4 of 4 4. Do the following: a) Identify the triode and saturation parts of the curve in the plot of the data captured in Part II. b) Estimate the drain-source resistance w It is the inverse of the slope of 𝐼 𝐷 versus 𝑉 𝐷? in the triode region. This resistance is sometimes named Ron in data sheets. c) Estimate the value of 𝜌 . It is the inverse of the slope of 𝐼 𝐷 versus 𝑉 𝐷? in the saturation region. d) Calculate 𝜆 using 𝜌 and 𝐼 𝐷 measurements. VII. After the lab On PSpice or LTSpice, Run “DC Sweep” simulations on the circuits built in lab . Include plots of your measured data and simulation results side by side on the same page so they are easily compared. Note: The “DC Sweep” s imulation will emulate you turning a potentiometer or varying the power supply to sweep voltages in lab.