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[[RF.Spice]]'s FM modulator takes an arbitrary input signal and generates a frequency-modulated sinusoidal signal at as its output. Â Place and connect all the parts as shown in the figurebelow. The DAC conversion bridge generates a pulse train of binary voltage levels 0V and +5V based on the input bit sequence. For the QAM modulator, you will use a 3GHz carrier frequency with a carrier amplitude of 5V. For the signal splitter, you will use the Wilkinson power divider you explored earlier in RF Tutorial Lesson 12. Set the center frequency of the Wilkinson power divider to fc = 3GHz and set its power ratio to K =1 for equal split between the two output ports.
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In this part of the lesson, you will use different waveforms as the input signal to the FM modulator. You will use the basic voltage source V1 to generate a sinusoidal waveform. Then you will replace it with a '''Pulse Generator''', a '''Ramp Generator''' and a '''Triangular Wave Generator''', all of which can be accessed from '''Waveform Generator Blocks > Basic Waveforms'''. Define each source one by one according to the waveform tables below:
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Run For each waveform, run a Transient Test of your modulator circuit with the following [[parameters]]:
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The results are shown in the figure figures below. Note that a very small time step ceiling make result in long computation time. Here we have chosen a '''Step Ceiling''' of 10ps to speed up for all the simulationfour different waveforms.
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[[File:SysTUT7 7.png|thumb|750px|The graph of the digital input binary sequence and the analog output voltage waveforms of the QAM FM modulator circuitwith a sinusoidal input.]]
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[[File:SysTUT7 8.png|thumb|750px|The graph of the digital input binary sequence and the analog output voltage waveforms of the QAM FM modulator circuitwith a pulse (square wave) input.]]
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[[File:SysTUT7 9.png|thumb|750px|The graph of the digital input binary sequence and the analog output voltage waveforms of the QAM FM modulator circuitwith a ramp (sawtooth wave) input.]]
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[[File:SysTUT7 10.png|thumb|750px|The graph of the digital input binary sequence and the analog output voltage waveforms of the QAM FM modulator circuitwith a triangular wave input.]]
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