The difference between the small-signal and large-signal s-parameters measurements

hi all...

is there a difference between the small-signal and large-signal s-parameters measurements..

Re: s-parameters

Hello Deeptimogia,

Yes their is lot of difference between the measurements

Small Signal S-Parameters:
The S-parameters represent the scattering coefficients for the N-port device/circuit.
A 50 ohm reference impedance is assumed in the computation of the S-parameters
unless a port termination other than 50 ohms is specified in the port.

small-signal S-parameters are based on a small-signal simulation of a linearized circuit.
Ex: Filter Passive circuits, LNA, etc


Large-Signal S-Parameters:
is used to compute the equivalent of an S-parameter under large signal excitation conditions.
The computation requires that the "From" port be an excitation port.
For example, the measurement of the complete set of S-parameters for a two port would
require two separate simulations where one simulation places an excitation on port one
(for measuring S21 and S11) and the second simulation places and excitation on port two
(for measuring S12 and S22). This measurement also allows the selection of the harmonic
frequency used for both the "From" port and the "To" port, enabling the measurement of
quantities like conversion loss or gain in mixers and multipliers.
This measurement can also be used to measure a large signal output return loss using two sources.

Large-signal S-parameters are based on a harmonic balance
simulation of the full nonlinear circuit. Because harmonic balance is a large-signal
simulation technique, its solution includes nonlinear effects such as compression.
This means that the large-signal S-parameters can change as power levels are
varied. For this reason, large-signal S-parameters are also called power-dependent
S-parameters.

The quasi- large-signal approach is the most accurate way to
measure the large-signal S-parameters for transistors, especially S12 S22.



---manju---

Re: s-parameters

thanks for relying..

so..that means..to build a nonlinear model for some device say HEMT..i need large signal S-parameter measurements..since this large signal model can be used in power amplifier design...

Re: s-parameters

How you can use s-parameters for device model development...If it is possible then use the Large signal S-parameters...
I think only Y-Parameters & netlist descriptions with some expressions can be used to model the Devices...


any way if you want to design Power Amplifier then you need have Nonlinear device model (spice) & S-parameters are not sufficient...



---manju---

Re: s-parameters

thanks manju...


one can have the model from s-parameters at various bias points...extrinsic are extracted first and then the y matrix of intrinsic is obtained...

thanks..the info was quite helpful..

Re: s-parameters

Hello Deepti,

Yes, you can develop using S-parameters of various bias condition files...
One such model development thesis paper available (attached), which may be useful for you....



---manju---

Re: s-parameters

hi manju..

i was already having that literature..was not quite helpful to me..
thanks nyways..

can u help me with modeling of MESFET as a switch...i have posted a msg related to this earlier...