Unfortunately you have not been very clear about what you want from a 100MHz PWM signal but here goes. As others have said, if you want a variable frequency signal about 100MHz from the chips onboard PWM then there is no way you can get it from a 32MHz core clock without external frequency multiplication but you do not mention any requirements for duty cycle control. So if you want a 100MHz clock I suggest you get a 100MHz crystal oscillator module and you can at least turn it on and off with a transistor circuit and a single I/O pin. If you however want a variable frequency at that rate then you might have to consider a VCO module with the control voltage driven by the PWM. Not too sure if they are still called the same but 'Mini Circuits' used to be a very good source for that sort of thing. However you will still have to contend with the available frequency range versus what your exact requirements are not to mention the question of resolution at that frequency and no control whatsoever over duty cycle. The last option would be to build your own VCO to your required specifications that does allow you full control of duty cycle (Unless you can find one of those) but at 100MHz these things can get very complex. If you are a student doing a one off project then you might just be able to tweak it but for production we usually employ an Engineer who does that sort of thing all the time.
