EE 2274 MOSFET BASICS

Transcription

1 Pre Lab: Include your CN with prelab. EE 2274 MOSFET BASICS 1. Simulate in LTspice a family of output characteristic curves (cutve tracer) for the 2N7000 NMOS You will need to add the 2N7000 model to LTspice if you have done it previously. a. Use a DC Sweep of Vdd from 0 to 10 volts in 100mv increments to change the drain-source voltage (V DS) X axis of the MOSFET curve. Y axis = I D in ma. b. Use the step sweep from 1 to 3 volts to change the gate to source voltage (V GS) of each curve in 200mv increments. c. un the simulation and then click on All and OK to display all the curves. d. In the plot window right click then select steps select the Vgs = 3V step. Use this curve to calculate Vtn or just set the V GS = 3.0V and not do the step command. e. V TN can be found by subtracting V DS of any curve from V GS of the curve at the point where the current I D begins to flatten out V TN = V GS V DS flat V GS step used = V DS used to calculate = V TN I D = at V TN Vds.include 2N7000.sub Vgs Vdd M1 2N ser=0 Vgs.step Vgs dc Vdd Figure 1 Page 1 of 5

2 2. Build a four resistor bias circuit (figure 2) for a NMOS. Design the circuit such that Vdd = 12Vdc,Vg=5V, Vds=5V, Id=10ma, Ig2=1ma, assume Vgs=2.4V. Set the value of I D by setting the value of S. Because Vs = Vg Vgs assume Vgs is almost constant so Vs is almost constant, so changing s will not change Vs but it will change Is and assume Id = Is. Set the Value of V DS by setting the value of D where V D = I D( D) and V DS = V DD V S V D. Include the design values and the standard 10% resistor values. Simulate in LTspice with (DC op pnt ).op and include schematic with currents and voltages (right click schematic - view Place.op Data Label), two simulations design value and standard values of resistors. Show your work. Vg g1 d M1 Vd Vdd 12Vdc 2N7000 g2 s Vs.op.include 2N7000.sub Figure 2 g1 g2 Design value Standard 10% value d s Design value Standard 10% value Vdd supply voltage V g1 voltage across g1 V g2 voltage across g2 V s voltage across s V d voltage across d V gs gate to source voltage V ds drain to source voltage Is Source current I g1 Current in g1 I d drain current Design values Calculated with standard values Page 2 of 5

3 3. Simulate in LTspice the NMOS Inverter shown below (figure 3). Instead of varying the drain-source voltage, vary the gate-source voltage. Use the DC sweep to vary the gate voltage V GS from 0 to 5V step = 100mv and plot this versus I D, and V DS with supply voltage Vdd=5 volt. Turn your graph in. What is the V TN voltage (just starts to conduct) for the 2N7000? How does this compare with 1e? V TN = Figure 3 Inverter I D = at V TN equired graphs: 1. I-V Characteristic curve of 2N7000 from LTspice. 2. (2 schematics) LTspice.OP simulation of 4 resister bias circuit with voltage and current displayed on schematic 3. DC sweep of NMOS Inverter Current 4. DC Sweep of NMOS Inverter Voltage Page 3 of 5

4 LAB Procedure MOSFET BASICS Part I. Characteristic Curve 1. Perform the characteristics I-V curves for the 2N7000 NMOS using the Tektronix curve tracer. Find the threshold voltage V TN (V GS where the MOSFET begins to conduct I D) Print curve. Set curve trace to N-FET, Is Max = 10ma, Vds max =10V, Vg/step = 0.1V, Offset = 1.8V, load=0.10, N Steps = 10. Use any socket, they are wired in parallel remember S = E, G = B, and D = C for the sockets. Part II. Construct Circuit 1. Build the four resistor bias circuit that you designed in the Pre-Lab figure 2. Measure all of the currents going into the FET (do not use current meter, measure the voltage across a known resister). Also, measure all of the node voltages. Verify that your design works. Note: Do not spread the leads of the NMOS transistor the outer leads will not always make contact. Part III. Inverter Circuit 1. Build the NMOSFET Inverter circuit figure 3 that you used in the pre-lab to observe the switching behavior of the FET set Vdd = 5Vdc. (a,b) Use Basic DC Sweep to step V GS from 0V to 5V with 100mv steps. (Use oscilloscope to verify the V GS sweep). ecord the Id use a multimeter to measure the voltage across a known resister (d) and calculate the drain current ( Id ) place a step inside the loop as the last step. Add Step - Processing Analog signals - Formula to calculate and produce a plot of the drain current, for a sweep plot calculate a scale factor (amps/volt) by hand for the voltage plot. Write this factor on the plot and turn in. a. Plot V GS verses I D. What is the V TN for the 2N7000? (V GS where the MOSFET begins to conduct I D ) b. Plot V GS verses V DS. What is V DS at turn-on (V GS =5.0V) and turn-off (V GS = 0.0V)? (c,d) Use a 1 khz square wave 5vpp, with 2.5 Vdc offset for V GS, (this will give you a 0-5 volt square wave). Use oscilloscope to monitor input V GS Ch1 and output V DS Ch2. c. What is the drain-source voltage from scope (V DS at turn-on and turn-off)? d. What is the rise time and fall time of the MOSFETS drain-source voltage measured at 10% and 90% of maximum Vds? Page 4 of 5

5 DATA SHEET EXPEIMENT MOSFET BASIC Name: Name: Instuctor: Class Day and Time: Date: Bench Number: CN: Part I. 1. Turn in graph. V TN = Part II. g1 measured g2 measured d measured s measured Vdd supply voltage V g1 voltage across g1 V g2 voltage across g2 V s voltage across s V d voltage across d V gs gate to source voltage V ds drain to source voltage Is Source current I g1 Current in g1 I d drain current Design values from prelab measured Part III. Scale factor for the DC Sweep plot = Include plot. Must include units. Turn-on (V GS =5.0V) Turn-off (V GS = 0.0V) III a V TN (measured) III a I d (on) I d (off) III b V ds (on) V ds (off) III c T f (fall Time) T r (rise time) III d V ds (on) scope V ds (off) scope equired plots: 1. I-V Characteristic of MOSFET 2. Plot of V GS verses I D 3. Plot of VGS verses V DS 4. Output rise time of MOSFET from scope 5. Output fall time of MOSFET from scope Page 5 of 5