6 002 Demo 06 Load set up Demo 06 set S SR SCS models Lecture 6 and 8 Agarwal Fall 00 Purpose This demo illustrates the various models of the MOSFET namely the S SR and SCS models The models are displayed on the scope by plotting the current iD taken as a voltage across a load resistor versus the voltage vDS with a sinusoidal drive on VS to display a line rather than simply a point The S and SR models are shown by switching vGS between voltages above ON state and below OFF state the MOSFET threshold voltage The SCS model is shown in a similar manner by incrementally increasing vGS from just below vT to some amount above it This shows the saturation current source region of the MOSFET not visible when larger values of vGS are used Steps 1 To show the switch model vIN is set to a large value and switched on and off The i v characteristic as seen from the drain to the source is shown on the scope The curve looks like an open circuit horizontal line and a short circuit vertical line accordingly 2 To show the switch resistor model vIN is set to a slightly smaller value and switched on and off The i v characteristic as seen from the drain to the source is shown on the scope The curve looks like an open circuit horizontal line and a resistor sloped line accordingly 3 To show the switch current source model vIN is set just below vT and increased incrementally to show a family of curves S model SR model SCS model Description MOSFET Switch S switch resistor SR Switch Current Source SCS models 1 Set FG2 High Z mode frequency 500 HZ Sine Amp 3 v p p Offset 1 5 v p p 2 Set FG1 High Z mode DC offset only press DC offset button and hold it until you hear the click a To show S model set FG1 dc offset to 5 v NOT MORE THAN 5 V IT WILL DAMAGE THE FET turn the switch S1 on the pc board to FG1 to show VGS VT and off to show VGS VT See Fg1 pictorial graph b To show SR model set FG1 dc offset to 2 6 v turn the switch on the pc board to FG1 to show VGS VT and off to show VGS VT See Fg1 pictorial graph c To show SCS model making various curves do the following The switch on the pc board should be set on FG1 ON roll FG1 dc offset voltage between 2 2 4 v by tenths i e 2 0 2 1 2 4 See Fg1 pictorial graph Note See below the sequence of button to change from 50 Ohm termination to High Z mode Cite as Anant Agarwal and Jeffrey Lang course materials for 6 002 Circuits and Electronics Spring 2007 MIT OpenCourseWare http ocw mit edu Massachusetts Institute of Technology Downloaded on DD Month YYYY Oscilloscope Setup CH V DIV OFFSET MODE FUNC MATH VERTICAL 1 off 1 0 DC off CH1 CH2 2 off 1 0 DC off F1 500 m 3 off 1 1 0 DC on F2 vs CH2 4 off 2 DC off CH2 CH3 Horizontal 6 0 2m Acquisition AUTO AUTO Waveform Generator Setup 1 2 4 HORIZONTAL 500mv 999 mv Trigger CH1 Power Supply Setup UNIT WAVE AMP OFFSET FG1 DCV 0 2 5V FG2 SIN 3 1 5 FREQ 1k 6 25 25 Hi Z 500 HZ Hi Z OUTPUT OFF Trigger INT INT See the sequence of buttons to be pressed 0 0 4v v High 50 Ohm Cite as Anant Agarwal and Jeffrey Lang course materials for 6 002 Circuits and Electronics Spring 2007 MIT OpenCourseWare http ocw mit edu Massachusetts Institute of Technology Downloaded on DD Month YYYY 5 S SR SCS MODELS 5 14 100 Ohm 7 CH2 7 14 2N7000 FG2 S1 2 2 17 S1 17 Fg1 FG1 VGS VT VGS Vt 2 ID ID ID 2 VGS VT VDS VGS VT VDS Note of pins on the PC board and BNC connectors BNC Pins Cite as Anant Agarwal and Jeffrey Lang course materials for 6 002 Circuits and Electronics Spring 2007 MIT OpenCourseWare http ocw mit edu Massachusetts Institute of Technology Downloaded on DD Month YYYY
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