Convert a PWM to analogue with double the voltage range?
A voltage doubler won't be effective especially if the PWM duty cycle 30% or less - the 7660 needs at least 1.5V to power it and that is the first problem. The second problem would be finding an op-amp with perfect rail-to-rail outputs. Again a problem made worse at low voltages.

Apart from anything else the 7660 converts its input to a negative voltage and that is of little use here.

The only solution I can think of is to provide a 10.5V supply to a rail-to-rail op-amp with a gain of +2.