NI SMA-2164 User Guide
12
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Terminating Signals
Termination of high-speed digital signals is necessary to prevent signal
reflections and force signal channels to a known state when no signal is
present. Pads for terminating resistors are connected to all DIO and control
channels on the NI SMA-2164. These pads are labeled in Figure 1 and are
shown in more detail in Figure 6.
Note
Proper termination needs are application-specific. For some special considerations
for choosing resistor values, refer to the
section.
Minimizing the Effects of Stubs
Stubs are unterminated tributaries from the original signal path. Stubs
decrease the signal quality of the system by adding reflections to the
transmission channels. To minimize the effect of stubs, termination is
placed at the end of the signal path.
Note
Refer to the
NI Digital Waveform Generator/Analyzer Help
for more information
about proper signal termination.
If your signal transmission line ends on the NI SMA-2164, you can use the
provided resistor pads to solder termination resistors. If your signal
terminates somewhere other than the NI SMA-2164, NI recommends
terminating the transmission line at the final signal destination. Each signal
pair is routed through a symmetric circuit, shown in Figure 5.
Differentially Terminating DIO and Control Signals
Resistors R80, R63, R64, and R69 in Figure 6 can be populated with
0402-sized resistors to provide termination. It is recommended that these
resistors are each populated with 50
Ω
resistors in order to provide the
expected 100
Ω
of differential termination.
