mos vs junction varactors

[ravet]

Hello
what are the disadvantages and advantages of the mos varactor and junction varactor?
and what is prefered in design of VCOs?

thanks

 

[Vamsi Mocherla]

The basic function of the varactors is to cause a voltage dependent capacitors. While a junction varactor has a predictable equation for its capacitance, a MOS cap is used only when there is weaker inversion(smaller voltage at the gate).

In this region a MOS varactor is highly linear in the sense that there is almost a linear relationship between voltage and capacitance. But the whole voltage range is very narrow.

For a junction cap( diode cap), the region is more wider for capacitance scaling but it is not a very linear relation.

 

[ravet]

The basic function of the varactors is to cause a voltage dependent capacitors. While a junction varactor has a predictable equation for its capacitance, a MOS cap is used only when there is weaker inversion(smaller voltage at the gate).

In this region a MOS varactor is highly linear in the sense that there is almost a linear relationship between voltage and capacitance. But the whole voltage range is very narrow.

For a junction cap( diode cap), the region is more wider for capacitance scaling but it is not a very linear relation.

thanks, but what is the importance of linearity of the c-v characteristics???