Atec Agilent-8722ES - Manual (Page 17)

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Agilent 8719ES, 8720ES, and 8722ES
Agilent 8719ET, 8720ET, and 8722ET
Time-domain (Option 010)
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
Two types of time excitation stimulus waveforms
can be simulated during the transformations, a
step and an impulse.
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
measurements 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
configuration. 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 frequency
span and the number of points. Range, in nanosec-
onds, is determined by:
1/∆F = (number of points in frequency domain – 1)
/frequency span (GHz)
Range resolution
The time resolution of a time-domain response
is related to range as follows: (for example, 0.3
nanoseconds versus 0.307 nanoseconds)
Range – resolution = time span/(number of points – 1)
Distance
Distance is related to time by the speed of light
and relative velocity. In space, V
rel
=1; for distance-
to-response in a 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
(filter) 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.
Options