What does Cgg, Cgd, Cgs and Cgb mean in Cadence Virtuoso print of a MOS device?

[Beardolphinaries]

Hi,
When I am using Cadence Virtuoso and print the operating point of the MOS device, I notice that there are several different capacitors

For example, Cgg, Cgd, Cgs and Cgb.

What do these mean?
Why some of them are nagetive? And seems that
Cgg=Cgd+Cgs+Cgb no matter the polarity of the values.

Can anybody give me some explanation please?
Thanks a lot.

 

[harmonics]

cgg-cgs

I read somewhere that the definition
Cxy = dQx/dVy
So sometimes you may get -ve capacitance following this definition.

 

[berryfan]

cgg in cadence

I also want to knew it .what's main capacitance we must cocern?I think is CGS and CGD

 

[marmot.liu]

mos model cgg

yes, Cgg are the total gate capacitance for a mos.I think Cgs is the most important, its value is also the biggest one.

Cgg : the total capacitance of a mos seen from the gate
Cgs : the capacitance between gate and source
Cgd : the capacitance between gate and drain
Cgd : the capacitance between gate and body(Substrate)