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In this tutorial, ac sources and the oscilloscope are introduced and measurement of ac quantities is illustrated. In this tutorial, you will
The Pulse Sources The EWB clock is available from the Sources parts bin as illustrated in Figure 15-1. When you click and drag it onto the EWB screen, the icon appears as shown. You can select the voltage amplitude, frequency, and duty cycle by double-clicking on the icon and setting the values in the Pulse Voltage dialog box. The Pulse Voltage dialog box is shown in Figure 15-2.  Figure 15-1 The clock source in the Sources parts bin.  Figure 15-2 Pulse Voltage dialog box. The clock source produces a pulse waveform that has a baseline of zero, as you can see in Figure 15-3, so that all the pulses are positive.  Figure 15-3 The clock source produces a positive pulse waveform. Another source of pulses available in EWB is the function generator. The difference is that the output of the function generator is an alternating waveform that varies equally above and below the zero axis, as shown in Figure 15-4.  Figure 15-4 The function generator produces an alternating pulse waveform. It does not have to be that way. The function generator will produce a 0-5 V pulse if it is set up for that function as in Figure 15-5. Note that the amplitude is set for 2.5 volts and the offset is set for 2.5 volts, producing a 0-5 V pulse.  Figure 15-5 Function generator as a clock pulse source. Example 15-1 Use EWB to illustrate the charging and discharging of a capacitor in response to a pulse input. Solution An RC integrator with a square wave input is shown in Figure 15-6. The RC time constant is selected so that the capacitor can fully charge and discharge during each pulse cycle. The period of the 1 kHz input is 1 ms. The capacitor must fully charge or discharge in one half of the period, 0.5 ms, so five time constants must be equal to or less than 0.5 ms. The circuit time constant is selected to be RC = 0.5 ms/5 = 100 s. In Figure 15-6, the red waveform is the input and the blue waveform is the output. They are superimposed so that the relationship can be easily observed. Figure 15-6 Illustration of a capacitor fully charging and discharging in response to a pulse input to an integrator. Simulation Connect the circuit in Figure 15-6 and run the simulation. Example 15-2 Use the resistor and capacitor in Figure 15-6 to construct a differentiator and observe the output waveform. Solution Connect the circuit in Figure 15-6 and run the simulation. Figure 15-7 Illustration of the capacitor fully charging and discharging in response to a pulse input to a differentiator. Simulation Connect the circuit in Figure 15-7 and run the simulation. Multisim/EWB Exercises
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. Observe the difference in the output waveform and explain.