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De-Embedding S-Parameters

This example shows you how to extract the S-parameters of a Device Under Test (DUT) using the deembedsparams function.

This example will use the S-parameter data in the file samplebjt2.s2p that was collected from a bipolar transistor in a fixture with a bond wire (series inductance 1 nH) connected to a bond pad (shunt capacitance 100 fF) on the input, and a bond pad (shunt capacitance 100 fF) connected to a bond wire (series inductance 1 nH) on the output, see Figure 1.

Figure 1: Device under test (DUT) and the test fixture.

This example will show how to remove the effects of the fixture in order to extract the S-parameters of the DUT.

Read the Measured S-Parameters

Create an 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 the Left Pad

Create a two port circuit object representing the left pad, containing a series inductor and 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 the Right Pad

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 the S-Parameters

De-embed the S-parameters of the DUT from the measured S-parameters by removing the effects of input and output pads (deembedsparams).

S_DUT = deembedsparams(S_measuredBJT,S_leftpad,S_rightpad);

Plot the Measured and De-Embedded S11 Parameters on a Z Smith® Chart

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 the Measured and De-Embedded S22 Parameters on a Z Smith Chart

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 the Measured and De-Embedded S21 Parameters in Decibels

hold off
clf                                     % Clear smithplot canvas
h1 = rfplot(S_measuredBJT,2,1,'-r');
hold on
h2 = rfplot(S_DUT,2,1);
legend([h1,h2],{'Measured S_{21}','De-Embedded S_{21}'})
legend show

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