Specifications

Appendix D
Wiring and Noise Reduction Methods
Separating Digital and Analog SCP Signals
Signals with very fast rise time can cause interference with nearby signal paths.
This is called cross-talk. Digital signals present this fast rise-time situation. Digital
I/O signal lines that are very close to analog input signal lines can inject noise into
them.
To minimize cross-talk, try to maximize the distance between analog input and
digital I/O signal lines. Figure D-1 shows that, by installing analog input SCPs in
positions 0 through 3 and analog output and digital I/O SCPs in positions 4 through
7, these types of signals can be separated by the width of the VT1419A module.
The signals are further isolated because they remain separated on the connector
module as well. Note that in Figure D-1, even though only 7 of the eight SCP
positions are filled, the SCPs present are not installed contiguously, but are
arranged to provide this digital/analog separation.
If it is necessary to mix analog input and digital I/O SCPs on the same side, the
following suggestions will help provide quieter analog measurements.
·
Use analog input SCPs that provide filtering on the mixed side.
·
Route only high level analog signals to the mixed side.
Appendix D 371
VT1533A
Digital I/O
SCP Pos 0 SCP Pos 1 SCP Pos 2
SCP Pos 3
VT1534A
PWM, Freq &
Totalizer
VT1531A
Voltage DAC
Analog Input and
Output
Digital Input and
Output
SCP Pos 7 SCP Pos 6 SCP Pos 5 SCP Pos 4
empty
Figure D-1: Separating Analog and Digital Signals
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