Cgs Cgd Which one is more important for Class-AB pa design?

[kwanmajun]

Recently i got a question about Cgs and Cgd, here is the question
"
Cgs Cgd Which one is more important for Class-AB pa design performance such as PAE, POUT and so on? Why?
How about for LNA circuit? Cgs Cgd which one is more important for LNA circuit performance, such as NF, gain... why?"

Please answers with details thanks~

 

[precision]

Re: Cgs Cgd Which one is more important for Class-AB pa desi

Recently i got a question about Cgs and Cgd, here is the question
"
Cgs Cgd Which one is more important for Class-AB pa design performance such as PAE, POUT and so on? Why?
How about for LNA circuit? Cgs Cgd which one is more important for LNA circuit performance, such as NF, gain... why?"

Please answers with details thanks~

Cgs is more important. Cgs normally is between input port G and ground, but Cgd is between input port G and output port D and can be effectively divided to two parts C1 and C2 by Miller Effect. C1 and C2 are between G/Ground and D/Ground respectively. Now C1 is much smaller than Cgs (because the Gain of the transistor).

About Class-AB PA design and Cgs, you can read Chengzhou Wang's (UCSD) Ph.D thesis "CMOS Power Amplifiers for Wireless Communications", please find it as the attachment here.

 

[ChaoFan]

hi, I think Cds is more important then Cgs, especially for Eff, Pout, wideband performance.

 

[kspalla]

Re: Cgs Cgd Which one is more important for Class-AB pa desi

hi, I think Cds is more important then Cgs, especially for Eff, Pout, wideband performance.

Effective Cgs responsible for upper cutoff freq. which contains Cds and Cgs. Cgs easily controlled by reverse bias but not Cds. So both are important