Sequid DTDR-65, Руководство по эксплуатации, Страница: 72 / 111

The performance and accuracy of the de-embedding algorithm depends on
the quality of the underlying S-parameters of the fixtures. Please find below
some recommendations to achieve the best possible results:
•
Required: make sure the upper cut-off frequency is greater than or
equal to the cut-off frequency of your TDR-device.
•
Required: make sure the lower cut-off frequency is less than or equal
to the frequency given by the formula f
min
= ( N
p
·
t
s
)
−
1
, where N
p
is
the number of points and t
s
the sampling time. Both parameters can
be found in the Oscilloscope Window (see section 3.5.2 ).
•
Recommended: better results can be obtained if the frequency incre-
ment is equal or less than f
min
.
8.3 Creating De-Embedding S-Parameters
Please note: the full 2-port measurement mode according to section 6.4 is required
to use this functionality.
The Seunis software basically can be used to measure 2-port S-parameters
and is therefore suitable to characterize fixtures as discussed in section 8.1 .
A typical use case is to calibrate the instrument at the end of the coaxial
cables where e.g. interchangeable components are connected between ca-
ble and DUT. The prerequisite is the fixtures to be characterized can be con-
nected to the 12TC-calibrated TDR-system (most likely via SMA-connectors).
To create the S-parameter set for de-embedding according to the require-
ments and recommendations stated in section 8.2 it is recommended to pro-
ceed as follows:
1. Perform a full 2-port calibration (12TC)
2. Set the number of averages to a high number (>1000)
3. Activate frequency domain smoothing (see chapter 7 )
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