Biomedical Engineering Reference
In-Depth Information
ectometer (TDR) [Strassberg, 1993] of Figure 4.40, which is often
used in the troubleshooting of LANs, injects a very sharp pulse V i into the transmission line
under analysis. Then an oscilloscope or a computer
The time-domain re
fl
fi
fitted with a high-speed A/D receives
the re
ected pulses contain the informa-
tion required to estimate the impedance of the line and its termination (Figure 4.37).
In contrast to TDR, network analyzers such as that in Figure 4.41 operate in the fre-
quency domain and enable exact measurement of the complex re
fl
ected pulses. The time delay and shape of the re
fl
cient as a
function of frequency, measurement of crosstalk between lines, and measurement of phase
skew between signals [Montgomery, 1982]. A network analyzer can also be used to iden-
tify tracks on which resonance problems could arise and to perform objective crosstalk
measurements.
fl
ection coe
PCB Track
Digital Storage Oscilloscope
Z r
V i
Z t
Time-Domain Reflectometer
Figure 4.40 In a time-domain reflectometer, a voltage step with very short rise time is injected into
a transmission line. After a certain delay, a reflected pulse adds up to the step. The timing and wave-
shape of the reflected pulse contain information regarding the characteristics of the transmission line
and of the termination.
Computer
Frequency
Control
Tracking
Receiver
V
V
V t
i
r
Z t'
Z
t"
Directional
Coupler
Directional
Couplers
Z
Z
R'
R"
VCO
Ramp
Network Under Test
Sweep Generator
Frequency-Domain Network Analyzer
Figure 4.41 In a frequency-domain RF network analyzer, a sweeping sinusoidal signal is injected into the input of the transmission line
leading to the subnetwork under test. Directional couplers feed a synchronized RF receiver with samples of the incident, re
fl
ected, and trans-
mitted portions of the signal. A computer is used to calculate and display the complex re
fl
ection and transmission functions, as well as other
relevant parameters.
 
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