Pulse Position Modulator Simulation output

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ianllmyspite

Joined Jul 7, 2020
15
ppm.pngppmsignalandoutput.png

Hi, I'm trying to build a Pulse position modulator circuit using LTSpice (required simulator). This is what I have done so far. The vout isn't right as the position of the pulses should be varying and width/amplitude is constant in PPM. Anything wrong with my circuit that I should change?
Help would be very much appreciated. Thank you!
 

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crutschow

Joined Mar 14, 2008
27,956
That circuit basically changes the width of the pulse output versus the input signal.
Why did you think it would change only the pulse position?
 

crutschow

Joined Mar 14, 2008
27,956
is my circuit wrong?
For generating a PPM signal, yes.
Where did you get it?

One way to generate a PPM signal is to configure the 555 as a triggered one-shot, and trigger if from a comparator (e.g. LM339/393) with a triangle-wave at one input at the pulse frequency, the other input with a sinewave at the modulation frequency.
If you use a single supply for the comparator, then both those signal voltages cannot go below ground (negative voltage).
 
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