high voltage pump design

hi all
i have design a dickson pump for high voltage, which input is 1.8v, and output is 20v. but the ripple of output is bigger than 100mv, how i can make it small than 50mv.

thanks everyone

I got a patent on a polyphase pump which in silicon (SOI)
made 70V off 3.3V with almost invisible ripple. At 1.8V you
really want synchronous switches instead of diodes (I found
low-VT (between regular and "zero" / native) held the best
compromise between forward pumping voltage efficiency
(Vdd-VT) and leak-back (VT and subthreshold slope).

Not a Dickson implementation per se; that's where I
started but at the high stage count it became clear that
a different topology was wanted. Dickson pumps pay too
high a "tax" when drive levels approach rectifier forward
voltage.

If you want to play with the idea, it'll probably work for you
(in the end; some engineering required). If you want to put
it in a product for sale, expect to hear from my former
employer's lawyers.