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this example shows you how to extract the s-parameters of a device under test (dut). first, read a touchstone® file into a sparameters object, second, calculate the s-parameters for the left and right pads, third, de-embed the s-parameters using the function and finally display the results.

this example uses the s-parameter data in the file that was collected from a bipolar transistor in a fixture with a bond wire (series inductance of 1 nh) connected to a bond pad (shunt capacitance of 100 ff) on the input, and a bond pad (shunt capacitance of 100 ff) connected to a bond wire (series inductance of 1 nh) on the output, see figure 1.

figure 1: device under test (dut) and the test fixture.

this example will also show how to remove the effects of the fixture in order to extract the s-parameters of the dut.

read measured s-parameters

create a sparameters object for the measured s-parameters, by reading the touchstone® data file, samplebjt2.s2p.

s_measuredbjt = sparameters('samplebjt2.s2p');
freq = s_measuredbjt.frequencies;

calculate s-parameters for left pad

create a two port circuit object representing the left pad, containing a series inductor and a shunt capacitor. then calculate the s-parameters using the frequencies from samplebjt2.s2p.

leftpad = circuit('left');
add(leftpad,[1 2],inductor(1e-9));
add(leftpad,[2 3],capacitor(100e-15));
setports(leftpad,[1 3],[2 3]);
s_leftpad = sparameters(leftpad,freq);

calculate s-parameters for right pad

create a two port circuit object representing the right pad, containing a series inductor and shunt capacitor. then, calculate the s-parameters using the frequencies from samplebjt2.s2p.

rightpad = circuit('right');
add(rightpad,[1 3],capacitor(100e-15));
add(rightpad,[1 2],inductor(1e-9));
setports(rightpad,[1 3],[2 3]);
s_rightpad = sparameters(rightpad,freq);

de-embed s-parameters

de-embed the s-parameters of the dut from the measured s-parameters by removing the effects of input and output pads ().

s_dut = deembedsparams(s_measuredbjt,s_leftpad,s_rightpad);

plot measured and de-embedded s11 parameters on z smith® chart

use the function to plot the measured and de-embedded s11 parameters.

figure
hs = smithplot(s_measuredbjt,1,1);
hold on;
smithplot(s_dut,1,1)
hs.colororder = [1 0 0; 0 0 1];
hs.legendlabels = {'measured s11','de-embedded s11'};

plot measured and de-embedded s22 parameters on z smith chart

use the smithplot function to plot the measured and de-embedded s22 parameters.

figure
hold off;
smithplot(s_measuredbjt,2,2)
hold on;
smithplot(s_dut,2,2)
hs = smithplot('gco');
hs.colororder = [1 0 0; 0 0 1];
hs.legendlabels = {'measured s22','de-embedded s22'};

plot measured and de-embedded s21 parameters in decibels

use the function to plot the measured and de-embedded s21 parameters.

figure
hold off;
h1 = rfplot(s_measuredbjt,2,1);
hold on;
h2 = rfplot(s_dut,2,1);
legend([h1,h2],{'measured s_{21}','de-embedded s_{21}'});

$figure contains an axes object. the axes object with xlabel frequency (ghz), ylabel magnitude (db) contains 2 objects of type line. these objects represent measured s_{21}, de-embedded s_{21}.$