Direct modulation in PLL without up conversion mixer

What system is feasible in implementing direct modulation in PLL without up conversion mixer?
GMSK? QPSK? or others?
Thanks

Hello,

You could use translational PLL for constant envelope modulation like GMSK and QPSK

yeah i agree with RFCMOS , PLL can only modulate the phase and frequency ,

but others like QAM and so on , no

Khouly

i think the two below is right!