RF Toolbox™

s2tf

Convert S-parameters of 2-port network to voltage transfer function

Syntax

tf = s2tf(s_params, z0, zs, zl,option)

Description

tf = s2tf(s_params, z0, zs, zl,option) converts the scattering parameters, s_params, of a 2-port network into the voltage transfer function of a 2-port system. The transfer function represents the normalized voltage gain of the system. The following figure shows the setup for computing the transfer function, and the impedances and voltages used to define the gain.

The impedances in the figure are optional arguments to the s2tf function and are defined as follows:

• z0 is the reference impedance of the S-parameters.

• zs is the source impedance.

• zl is the load impedance.

The default value of these impedances is 50 ohms.

The voltages in the figure are defined as follows:

• V_l is the output voltage across the load impedance.

• V_s is the source voltage.

• V_in is the input voltage of the 2-port network.

The definition of the transfer function is determined by the optional option argument.

option can be

• 1 — The transfer function is the gain from the output voltage, V_a, of the source across a conjugate-matched load to the output voltage of the 2-port network in the preceding figure for arbitrary source and load impedances:

  

  The following figure shows how to compute V_a as the output voltage of the source across a conjugate-matched load (Z_la = Z_s*):

  

  In terms of S-parameters and impedance values, the transfer function is as follows:

  

  where

  

  The following equation shows how the preceding transfer function is related to the transducer gain computed by the powergain function:

  

  Notice that if Z_l and Z_S are real, .

• 2 — The transfer function is the gain from the source voltage to the output voltage for arbitrary source and load impedances:

  

  You can use this option to compute the transfer function by setting zs to 0. This setting means that and .

The default value of option is 1.

See Also

s2t

s2y