In pulse amplitude modulation, the amplitude of individual pulses in the pulse train is varied from its default value in accordance with the instantaneous amplitude of the modulating signal at sampling intervals. The width and position of the pulses is kept constant.

The PAM transmitter design is very simple since the very act of sampling the modulating signal at regular intervals produces pulse amplitude modulation. Main advantages of PAM are simple transmitter and receiver designs. PAM is used to carry information as well as to generate other pulse modulations.

PAM Generation with DspSee

Generating PAM

You can use two SigGen modules to generate a pulse amplitude modulated signal, and use the Plot module to display them. The following example generates a sine wave and a pulse train, uses first one to modulate the later and plots them.

You can also use other modules to process the generated data. For example, you can save the data in binary or text format and also perform various measurements.

Open the Modulation-PAM.dsp project in DspSee to see this example in action. Click to download DspSee dsp software.

Below is a description of the Modulation-PAM.dsp project file. Feel free to change it to try different things.

File starts ->

//Modulation-PAM.dsp //Copyright www.aubraux.com //DspSee sample file. Shows generation of pulse amplitude modulation with SigGen module. //Requires SigGen and Plot modules.
//Pulse Train Generator
load wc="SigGen"	//Loads the SigGen module. This module can generate waveforms of different shapes.
wc.type="pulse"	//Sets signal type
wc.freq=10.01M	//Sets frequency to 10.01 MHz
wc.pk2pk=2	//Sets peak-peak voltage to 2V
wc.offset=0	//Sets DC offset voltage to 0V
wc.mod.type="pam"	//Sets modulation type
wc.gui.more=1	//Shows more advanced settings
wc.gui.wnd="sg"	//Sets the gui window name
wc.gui.title="Pulse Setup"	//Sets the gui window title
wc.gui.move(500,0)	//Moves the window to (x=500, y=0)

//Modulating Signal Generator
load wm="SigGen"	//Loads the SigGen module. This module can generate waveforms of different shapes.
wm.set("sine",999K,1000,100M)	//set(signal type, frequency, record length, sample rate)
wm.pk2pk=2	//Sets peak-peak voltage to 2V
wm.offset=0	//Sets DC offset voltage to 0V
link wc.mod.src=wm.out	//Links wc synth's modulation input port to wm synth's output port
wm.gui.wnd="sg"	//Sets the gui window name
wm.gui.title="Mod Signal Setup"	//Sets the gui window title
wm.gui.move(500,0)	//Moves the window to (x=500, y=0)

//Plot
load p1="Plot"	//Loads the Plot module. This module can display input data in various formats.
p1.plot.title="Plot Window"	//Sets the title of the plot window
p1.setup.title="Plot Setup"	//Sets the title of the plot setup window
link p1.src.ch1=wm.out	//Links the mod signal output to Plot input
link p1.src.ch2=wc.out	//Links the carrier signal output to Plot input
p1.ch1.label="Mod Input"	//Sets the Plot ch1 label
p1.ch2.label="PAM Output"	//Sets the Plot ch2 label
p1.ch1.vposition=0	//Sets ch1 vertical position to middle
p1.ch2.vposition=0	//Sets ch2 vertical position to middle
p1.setup.move(280,0)	//Moves the plot setup gui to (x=280, y=0)
p1.plot.move(0,220)	//Moves the plot window to (x=0, y=220)
p1.plot.size(1000,420)	//Resizes the plot window to (width=1000, height=420)

<- File ends

Another Example using Schematic Editor

pam pulse amplitude modulation schematic

The above schematic is another example of generating pulse amplitude modulation. As you can see, the schematic based approach is very simple. Just add the desired modules from the module list, and connect them with the wires the way you want.

That's it, you are ready for the fun. Just click on the Run button on the toolbar to view the signal. Open the file Modulation-PAM.dsp in the Sch folder to load this example.