1

Why aremy S-parameters

so noisy?

This slide set illustrates that nonlinear behaviour shows up as “deterministic noise” in S-parameters measurements.

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S-par measurement #1FET Vg = -0.6V, Vd = 2.0V, Id = 28mA

500MHz-18GHz (100MHz spacing)

Source @ -20 dBm

S21

(dB

)

A first S-parameter measurement is performed on a biased FET, from 500MHz to 18 GHz with 100MHz of frequency spacing, applying -20dBm at source output.This slide shows the measured S21 parameter in dB as function of frequency.The gain of the transistor decreases smoothly from 11.5 dB to 6dB.

3

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S-par measurement #2FET Vg = -0.6V, Vd = 2.0V, Id = 28mA

500MHz-18GHz (100MHz spacing)

2 measurements plot on top of each other with Source @ 0 dBm

Source @ -20 dBm

S21

(dB

)

A second S-parameter measurement is performed on the same device, using the same frequency grid, but applying 0dBm at the source output. The device is in compression for this input level.This slide shows a comparison of the resulting S21 parameter as function of frequency for the two measurement.One can observe a noisier S21 parameter for the second measurement.Moreover, a third S-parameter measurement is performed with 0dBm at Source output. The resulting third S21 parameter is exactly the same as in case of the second measurement.Nonlinear behaviour shows up as “deterministic noise” in S-parameter measurements.

4

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Conclusions

Nonlinear behaviourshows up in

S-parameter measurementsas “deterministic noise”