6.4 Time Domain Transformation
The Analyzer measures and displays parameters of the DUT in frequency domain. Time
domain transformation is a function of mathematical modification of the measured
parameters in order to obtain the time domain representation.
For time domain transformation Z-transformation and frequency domain window
function are applied.
The time domain transformation can be activated for separate traces of a channel. The
current frequency parameters (S11, S21, S12, S22) of the trace will be transformed into the
time domain.
Note Traces in frequency and time domains can simultaneously
belong to one channel. The stimulus axis label will be
displayed for the active trace, in frequency or time units.
The transformation function allows for setting of the measurement range in time domain
within Z-transformation ambiguity range. The ambiguity range is determined by the
measurement step in the frequency domain:
The time domain function allows to select the following transformation types:
§Bandpass mode simulates the impulse bandpass response. It allows the
user to obtain the response for circuits incapable of direct current
passing. The frequency range is arbitrary in this mode. The time domain
resolution in this mode is twice lower than it is in the lowpass mode;
§Lowpass mode simulates lowpass impulse and lowpass step responses.
It is applied to the circuits passing direct current, and the direct
component (in point F=0 Hz) is interpolated from the start frequency
(Fmin) of the range. In this mode the frequency range represents a
harmonic grid where the frequency value at each frequency point is an
integer multiple of the start frequency of the range Fmin. The time
domain resolution is twice higher than it is in the bandpass mode.
The time domain transformation function applies Kaiser window for initial data
processing in frequency domain. The window function allows to reduce the ringing
(side lobes) in the time domain. The ringing is caused by the abrupt change of the data
at the limits of the frequency domain. But while side lobes are reduced, the main pulse
or front edge of the lowpass step becomes wider.
The Kaiser window is described by β parameter, which smoothly fine-tune the window
shape from minimum (rectangular) to maximum. The user can fine-tune the window
shape or select one of the three preprogrammed windows:
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