PWM Modulator Simulation in Multisim 11: Issues with Comparator and Mixed Signal Grounding

Trying simulation of PWM modulator circuit (for audio design), and if the triangle signal is come from difficult analog circuit, I have good result. But I tried simplest oscillator design with much better triangle signal output. I using TTL/CMOS NAND chips for simulation. The transient analysis have very good output while I analyzing the TTL/CMOS oscillator only, if I continues with analog comparator, I lost the benefit of this solution. Please help what wrong with my simulation method. See images. I made "independent" DC power sources for comparator chip only. After, the output of digital signal changed to perfect again, but the comparator doesn't works, I have no PWM output. If I made common ground for comparator and signal generator part, the triangle signal will be non-usable again. Please help if this mixed signal problem can be solved on Multisim 11. Thanks!

Hi Leslie,

Is the schematic of the entire circuit show in the image that you attached? I did not see a comparator.

Hello,

Yes, I cutted the comparator, but here is the new attachment. The triangle output after C3 connected to the comparator input. If the comparator's and the signal generator's have common ground, the triangle signal going wrong like in the images.