How to Generate Pulse Width Modulation?

What are you trying to acheive and why...
If this is purely educational you will get more value from playing with simple CMOS inverters to make oscillators and PWM circuits.
Using 2 function generators seems like using a sledge hammer to crack a nut and will probably teach you little.

Search the web for cmos oscillator pwm and such like.

Del

I do almost everything this way and I love how easy it is to apply simulations to real circuits and visa versa. I have used an SG3525 IC, but now I have found that I can get decently balanced push-pull MOSFET drive just using the 74C14 CMOS chip running two interlinked oscillators in a way similar to the famous 2 transistor oscillator.

It is for educational purpose, working on generation of pwm.

Trying to use the 2 XR-2206 to replace the 2 function generator and achieving similar pwm outcome.

I don't know how much you are into electronics...but I'd use a hex inverter (cmos) and a few Rs Cs and pot and a trimmer or two maybe a signal diode. Or play with a 555 timer. If you are controlling a motor the pwm will need tweaking to suit your particular motor/gearbox/load. I built a controller for an electric golf trolley, it turned out that the speed range required was from about 70% to 100% the first 69% didn't get it moving!(a quick search found Microchip AN807... an application note for a bi-directional pwm speed controller based on a 555 with 1 other chip and overcurrent sensing too...maybe overcomplex..but it shows that there is plenty of stuff out there).

Often the 'big' chips have incomprehensible data sheets, are too clever for their own good and teach you little. (EG they will show you how to use 1 specific chip rather than a family of chips and discrete components.

A while back I wanted to build an intelligent(ish) battery charger..I got a big fancy all singing all dancing chip...the application notes were hopeless ... In the end I built my own (simple) two stage charger.

Someone may wish to put an alternative view...

Del

No disagreement here. It is much easier to add what I need to simple CMOS Schmitt trigger gates and to quite completely understand what is happening than to try to decipher pre-made dedicated-purpose chips.

See if you can find SG2524 (TI part) or similar. I've used this and other PWM IC's, and I recall that at least one data sheet had application notes which explained the operation very clearly. I've also built them from scratch using a handful of IC's. I never got the performance out of a 555 that I had hoped for, and I tricked it out a bunch of different ways, but it is a very versatile little bugger.

If you generate your own triangle wave form (let's say 50 kHz) and you compare its amplitude to a modulating signal (let's say DC to 500 Hz) which ranges in amplitude from 0 to 100%, then the comparator output will have a pulse width linearly related to the modulating signal.