RF Toolbox 2.6

De-Embedding S-Parameters

The S-parameter data in the file 'samplebjt2.s2p' 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 demo shows you how to remove the effect of the fixture and extract the S-parameters of the DUT.

Contents

Create RF Objects

Create a data object for the measured S-parameters, by reading a Touchstone® data file 'samplebjt2.s2p'. Then create two circuit objects, one each for the input pad and output pad.

measured_data = read(rfdata.data, 'samplebjt2.s2p');
input_pad = rfckt.cascade('Ckts', {rfckt.seriesrlc('L', 1e-9), ...
    rfckt.shuntrlc('C', 100e-15)});  % L = 1 nH, C = 100 fF
output_pad = rfckt.cascade('Ckts', {rfckt.shuntrlc('C', 100e-15),...
    rfckt.seriesrlc('L', 1e-9)});    % L = 1 nH, C = 100 fF

Analyze the Circuit Objects in Frequency Domain

ANALYZE the input pad and output pad circuit objects at the frequencies the S-parameters of the BJT are measured.

freq = measured_data.Freq;
analyze(input_pad, freq);
analyze(output_pad, 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). Then create a data object for plotting the de-embedded S-parameters.

z0 = measured_data.Z0;
input_pad_sparams = extract(input_pad, 'S_Parameters', z0);
output_pad_sparams = extract(output_pad, 'S_Parameters', z0);
de_embedded_sparams = deembedsparams(measured_data.S_Parameters, ...
    input_pad_sparams, output_pad_sparams);
de_embedded_data = rfdata.data('Z0', z0, 'S_Parameters', ...
    de_embedded_sparams, 'Freq', freq);

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

fig = figure;
h = smith(measured_data, 'S11');
set(h, 'Color', [1 0 0]);
hold on;
h = smith(de_embedded_data, 'S11');
set(h, 'Color', [0 0 1]);
l = legend; legend(l, {'Measured S_{11}', 'De-Embedded S_{11}
'});
legend show;

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

hold off;
h = smith(measured_data, 'S22');
set(h, 'Color', [1 0 0]);
hold on;
h = smith(de_embedded_data, 'S22');
set(h, 'Color', [0 0 1]);
l = legend; legend(l, {'Measured S_{22}', 'De-Embedded S_{22}
'});
legend show;

Plot the Measured and De-Embedded S21 Parameters, in Decibel, on an X-Y Plane

hold off;
h = plot(measured_data, 'S21', 'db');
set(h, 'Color', [1 0 0]);
hold on;
h = plot(de_embedded_data, 'S21', 'db');
set(h, 'Color', [0 0 1]);
l = legend; legend(l, {'Measured S_{21}', 'De-Embedded S_{21}
'});
legend show;

close(fig);