Large Signal S-Parameters

[WalterChan]

large signal s22

Can anyone give me the definition of the large signal s parameters, LSSP?

I am quite confused by the LSSP, especially by the "S22". As far as I know, S22 is the port 2 return loss, where there is no input at the port 1. But for "large signal" condition, the amplifier is drived by high input power. So the "large signal S22" is quite confusing. Any comment?

What exactly information the LSSP can give us?

 

[harmony]

hello,
as u already know s-parameters (or small-signal s-paarmetrs) r only applied to linear systems, but wht if we need to charecterize any nonlinear system ?
like transistors, diodes, and many microwave systems.
4 that reason u ll need to apply some nonlinear analysis methods to linearize that system & obtain the needed s-parameters, one of the fameous techniques is (harmonic balance) which is already used by ADS.
therefore, LSSP r considered to be the s-parameteres for any nonlinear systems at higher freqeuncy


this document can help u 2 understand it man

 

[WalterChan]

From the LSSP.pdf
"The simulator performs the following operations to calculate the large-signal
S-parameters for a two-port:
• Terminates port 2 with the complex conjugate of its reference impedance.
Applies a signal with the user-specified power level P1 at port 1, using a source
whose impedance equals the complex conjugate of that port’s reference
impedance. Using harmonic balance, calculates the currents and voltages at
ports 1 and 2. Uses this information to calculate S11 and S21.
• Terminates port 1 with the complex conjugate of its reference impedance.
Applies a signal of power P2=S212P1 at port 2 using a source whose
impedance equals the complex conjugate of the reference impedance of port 2.
Using harmonic balance, calculates the currents and voltages at ports 1 and 2.
Uses this information to calculate S12 and S22."

I am confused by the above S12 and S22 LSSP simulation method again. It mentions that the port 1 is conjugated matched. However, in most nonlinear applications, i.e. class B, C, F power amplifier, the PA is driven by very high power otherwise the device cannot be turned on. The bias point of the PAs are also changed by the input power. I cannot see the above method has considered this effect.

I wouldn't say the above LSSP simulation method is useless. But I think it is only useful for class A application, in which device is always turned on. Any comment?

 

[harmony]

hello,
i ve never gone through any amplifier design, but rather mixers, & could find LSSP simply via that mean, my be u can search 4 any specialized tutorials that could help u in understanding this concept 4 amplifiers

this web page can be helpful
www.rfic.co.uk