varactor in standard CMOS process

[butterfish]

Hello everyone,

I need design a 10~20pf varactor on chip, between a 27MHz signal to GND.
Anyone knows how to design it?
Can I use the standard N+/Psub diode as varactor?

Thanks a lot!

 

[stober]

diode cannot vary from 10 to 20pf, the range is huge.

 

[butterfish]

Dear stober

Thanks for your reply!
which range is huge? diode or 20pf?
how about the pull range of N+/Psub diode? Do you have any C/V curve?
Could you explain more clearly?

Thanks!