6.002 Demo# 04 Nonlinear Device Lectures 6, 7 (load set up demo#04L.set) Purpose: In this demo, a nonlinear device (a photo-transistor) is examined to motivate the concepts of linearization and small-signal models. The nonlinear transfer characteristic for the system including the photo-transistor is shown on the scope. A music signal is then applied at the input, and the output is shown as a function of the input (as a segment of the transfer characteristic). The output is also sent to a speaker. The nonlinearities are then seen on the scope and heard as distortion, by adjusting the amplitude and bias of the input. It is an interesting aside to show (by blocking the light beam) that the music is in fact being sent as a modulation of the light intensity. Steps: 1. Using a large sinusoid, show on the scope the transfer characteristic of the nonlinear device, along with the input sinusoid and distorted output waveform. The tone can also be played through the speaker, so the distortion can be heard. (Stop here in lecture 6 to show nonlinear analysis). 2. (Do this in lecture 7). Reduce the amplitude of the sinusoid to show that (via small-signal linear approximation) the output is an almost perfectly faithful (ignoring scaling) copy of the input. 3. Switch the input from the sinusoid to music (CD player) in which distortion is easily heard. Adjust the amplitude to show the effect of the nonlinearity. Music Signal LED Sinusoidal input Description: phototransistor transfer characteristic AMP distorted output Nonlinear resistors, diodes, load line analysis, small signal. Linearization of Nonlinear Device (small-signal): Music played through optical connection Note: see schematic diagram next page for more detail; Fg1 Oscilloscope Setup CH 1 on V/DIV 1 OFFSET MODE FUNC -1.07 V DC off MATH VERTICAL HORIZONTAL 2 on 200 mV 214.7 mV DC off 3 off off 4 off off Horizontal: 5ms Acquisition: AUTO AUTO Waveform Generator Setup UNIT WAVE AMP FG2 Sin 500 mV 4 Trigger: CH1 Power Supply Setup OFFSET 0 FREQ 500 Hz +6 +5 +25 +15 -25 -15 OUTPUT Trigger: INT Note: Jeff starts with 6 v Supply set @ 2.7 V and amplitude of FG2 @ 500 mV. Later he changed the amplitude of FG2 to show distortion. Non Linear Device 5V (19 ) * 10 K 7 100 K 100 Ohm 1000 uF 1000 uF 1K +15 V 741 100 K (5) * 5 50 K - 15 V Pre Amp (2) * (2) * (2) * (2) * AMP 22 CH4 * Note: # of pins and BNC connectors BNC () Pins 4A) Set FG2 = 500 HZ sine Amp = 1.5 v P-P @ 50 Ohm 4B) Set FG2 = 500 HZ sine Amp = 1 v P-P @ 50 Ohm Prof. Agarwal Fall 00

6.002 Demo# 04: Nonlinear Device

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