3-4
Making Time Domain Measurements
Introduction to Time Domain Measurements
The time domain measurement shows the effect of each discontinuity as a function of time (or distance),
and shows that the test device response consists of three separate impedance changes. The second
discontinuity has a reflection coefficient magnitude of 0.035 (i.e. 3.5% of the incident signal is reflected).
Marker 1 on the time domain trace shows the elapsed time from the reference plane (where the calibration
standards are connected) to the discontinuity and back: 18.2 nanoseconds.
The analyzer has three frequency-to-time transform modes:
• Time domain bandpass mode simulates the time domain response of an impulse input and is designed
to measure band-limited devices. Although this mode is the easiest to use, it results in less time domain
resolution than low pass mode, and may result in some magnitude errors at low frequencies when gating
is used. For devices that are not band-limited, one of the low pass modes is recommended.
• Time domain low pass step mode simulates the time domain response of a step input. As in a traditional
TDR measurement, the distance to the discontinuity in the test device, and the type of discontinuity
(resistive, capacitive, inductive) can be determined.
• Time domain low pass impulse mode simulates the time domain response of an impulse input (like the
bandpass mode). Both low pass modes yield better time domain resolution for a given frequency span
than does the bandpass mode. In addition, when using the low pass modes, you can determine the type
of discontinuity. However, these modes have certain limitations that are defined in
"Time Domain
Bandpass Mode" on page 3-12.
The analyzer has one time-to-frequency transform mode:
• Forward transform mode transforms CW signals measured over time into the frequency domain, to
measure the spectral content of a signal. This mode is known as the CW time mode.
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