# lab3 - State University of New York at Stony Brook...

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State University of New York at Stony Brook ESE 211 Electronics Laboratory A Department of Electrical and Computer Engineering 2009 ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ 1 Lab 3: Measurement of AC signals 1. Objectives 1) Set up a signal generator and determine the generator equivalent circuit. 2) Set up an oscilloscope and measure AC parameters for rectangular and sinusoidal signals. 2. Introduction Signal generators are often designed to work with certain load impedance. It is common for signal generators to be programmable (i.e. there is user selectable option in device menu) to assume either 50 load or high Z load (i.e. nearly open circuit). If the actual load differs from this nominal (assumed by generator) value, the output voltage waveform would differs from the one shown on the generator display. Most often the difference would be only in the amplitude of the voltage but it is also possible to have distorted signal waveform. Therefore always rely on results of measurements by a scope no matter what is shown on the generator display. The signal generator on the lab bench allows two settings for the load impedance – a 50 or a Hi-Z (Z >> 50 ). For both settings the generator internal impedance is the same however in the first case the generator’s open circuit voltage will be twice as large as the value you set! The reason is that in order to generate 1V on 50 load with 50 internal impedance the generator must produce 2 V internally. Once the actual load is much larger than 50 , the voltage across it would be 2 V since generator would still be producing 2 V internally. You can check this argument yourself using simple circuit composed of ideal voltage source and voltage divider made of generator internal impedance and actual load.

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