Keysight DAQ970A - Page 215

Noise can be capacitively coupled between physically adjacent channels in a switching system. Noise can
be coupled between the switch contacts themselves (C
sw
) or between adjacent cabling (C
adj
).
Capacitive noise coupling is a function of area and proximity. A simple method to reduce the noise coup-
ling is to physically separate the switches and cables from each other. However, this may not be practical
for all applications.
Another solution is to keep large amplitude signals and small amplitude signals away from each other.
Group similar signals together (high voltages, low voltages, analog, and digital). If possible, use two sep-
arate switch modules; one for high-level signals and one for low-level signals. If you are using a single
module for mixed-signal switching, leave one unused, grounded channel between the groups. Also,
ground any unused channels on the module.
The DAQM901A and DAQM902A multiplexers have an additional relay, called a bank switch or tree switch,
which helps reduce channel-to- channel noise (C
adj
). The multiplexer channels are divided into two banks.
The bank switch isolates one bank of channels from the other, effectively removing any parallel adjacent
capacitance from the isolated bank. During a scan, the instrument automatically controls the bank
switches.
Keysight DAQ970A User's Guide 215
4Measurement Tutorials