Atec Agilent-8720D - Manual (Page 13)

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Option 010 time domain
With the time domain option, data from transmis-
sion or reflection measurements in the frequency
domain are converted to the time domain using a
Fourier transformation technique (chirp Z) and
presented on the display. The time domain response
shows the measured parameter value versus time.
Markers may also be displayed in electrical length
(or physical length if the relative propagation
velocity is entered).
Time stimulus modes
Standard stimulus
Two types of time excitation stimulus waveforms
can be simulated during the transformations, a
step and an impulse.
External stimulus
Other time excitation stimulus waveforms can be
accomplished using an external controller.
Low pass step
This stimulus, similar to a traditional time domain
reflectometer (TDR) stimulus waveform, is used to
measure low pass devices. The frequency domain
data should extend from DC (extrapolated value) to
a higher value, the upper limit being defined by the
test configuration used. The time domain response
shows the parameter value versus time (multiply
by the speed of light, c, to obtain electrical length
or by c and V
rel
to obtain physical length). The step
response is typically used for reflection measure-
ments only.
Low pass impulse
This stimulus is also used to measure low pass
devices. The frequency domain data should extend
from DC (extrapolated value) to a higher value, the
maximum frequency determined by the test config-
uration. The time domain response shows changes
in the parameter value versus time. The impulse
response can be used for reflection or transmission
measurements.
Bandpass impulse
The bandpass impulse simulates a pulsed RF signal
(with an impulse envelope) and is used to measure
the time domain response of band-limited devices.
The start and stop frequencies are selectable by
the user to any values within the limits of the test
set used. The bandpass time domain response also
shows changes in the parameter values versus
time. Bandpass time domain responses are useful
for both reflection and transmission measurements.
Time domain range
The “alias-free” range over which the display is
free of response repetition, depends on the fre-
quency span and the number of points. Range, in
nanoseconds, is determined by:
Range = 1/
∆
F = (Number of points in Frequency
Domain –1)/Frequency Span (GHz)
Range resolution
Time resolution of a time domain response (for exam-
ple, 0.3 nanoseconds versus 0.307 nanoseconds).
Range –resolution = time span/(number of points –1)
Distance
Related to time by speed of light and relative veloc-
ity; in space, V
rel
=1; for distance to response in
reflection measurement, multiply by 1 /
2
.
Distance = 3 x 10 8 m/sec x V
rel
x Time
Windows
The windowing function can be used to modify (fil-
ter) the frequency domain data and thereby reduce
overshoot and ringing in the time domain response.
Three types of windows are available—minimum,
normal, and maximum.
Gating
The gating function can be used to selectively
remove reflection or transmission time domain
responses. In converting back to the frequency
domain the effects of the responses outside the
gate are removed. The location and span of the
gate can be controlled by either setting the center
position and time span of the gate, or by setting
the start and stop time of the gate.
Analyzer options