6 002 Demo 10 Load Set up demo 10PG set Load Set up Demo 10AA set IDS vs VDS Load Line Agarwal Fall 00 Lectures 10 and 11 Purpose In this demo a picture of the MOSFET amplifier behavior is presented by displaying a load line over a set of premade MOSFET i v curves The load line crosses the family of MOSFET curves in the saturation region and ends in the ohmic region By using music as the amplifier input and by sending the output to a speaker distortion can be heard when the signal is outside the saturation region This is seen on the scope as the partial load line being in the saturation region no distortion in the ohmic region distortion or near the cutoff region distortion low volume As a fun and interesting aside we can show that classical music suffers much more perceptually than does say heavy metal Steps 1 Having previously aligned the load line with the stored MOSFET curves use the sinusoid input to show the entire load line 2 With the input sinusoid set to a small value turn on the speaker and adjust the bias of the input to show the amplifier behavior for the different MOSFET regions 3 Repeat the previous step using a classical music signal from the CD player noting the audio distortion 4 Switch to heavy metal music and point out this type of music does not perceptually distort much in showing this demo we have observed that the output to the speaker system of the class loads the circuit and makes it behave strangely Add a buffer to fix the problem MOSFET curves load line small music signal Description Small signal circuit models and analysis Load IVCURVE5 WFM from WAVEFORM MEMORY Connect CD output to the input of to EXT2 Red cable Connect CH3 output of MOSFET Amplifier using a Tee BNC to Mac Amp Speaker Make sure the FG1 is OFF Very important For music use CD1 10 for the first music later we play AC DC the razor edge 1 to show that Doesn t matter where you have the load line it sounds the same Note see Fg1 next page schematic diagram and pins being used 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 Note For Prof Agarwal load Demo 10AA set he starting with ONLY a dot by pressing FG2 offset bottom to zero Oscilloscope Setup CH 1 off V DIV 1 OFFSET MODE FUNC DC off CH2 CH3 4 451 DC off F1 1k F2 vs CH3 1 3 on 2 DC on 4 off 200 mV 611 mV DC off 670 mV Horizontal 1 m Acquisition FG2 SIN AMP 2 HORIZONTAL 1 97 2 67 3 91 Trigger CH4 Waveform Generator Setup WAVE VERTICAL 3 2 on UNIT MATH Power Supply Setup OFFSET 50m 100m 0 FREQ 1k 6 2 08 25 25 OUTPUT 6 on Trigger INT Note We had to use our amplifier and speaker set up because the 10 250 system stop working and also caused our amplifier MOSFET on demo board to go bad Note Use CD 1 Piano music instead violin for Prof Lang 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 6 Vdc from 25 1 IDS vsVDS Load Line 2K 100 uF CH3 20 20 2N7000 7 7 1K To Amp Speaker 22 22 6 Vdc 2 2 13 13 14 Note We don t need pre amp for this demo FG2 CD Player 2 Note of pins on the PC board and BNC connectors Make sure FG1 is OFF 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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