ADLINK PCIe-7350 - Manual (Page 82)

72 Function Block and Operation Theory
3.12 Termination
Proper termination is very important for applications using high-
speed digital data transfer to eliminate the signal reflection caused
by cables, wiring, connectors, or PCB traces and improve signal
quality.
The output impedance (source impedance) of the PCIe-7350 is 50
Ω and the characteristic impedance of the SCSI-VHDCI cable is
also 50 Ω. When you connect to a DUT with 50 Ω input imped-
ance, the best impedance matching will be achieved, but the volt-
age level sensed by the DUT will be half of the PCI-7350’s output
voltage due to voltage-divider principles. You can also connect to
a DUT with a high impedance (at least 1 - 100 KΩ) if precision tim-
ing and excellent signal integrity is not so critical. The voltage level
sensed by the DUT will be almost the same as the output voltage
of the PCIe-7350.
The input impedance of the PCIe-7350 is 10 K Ω, which is a high
impedance. So with a high impedance 10 KΩ load termination, the
external source impedance of DUT should match the characteris-
tic impedance (50 Ω) of the SCSI-VHDCI cable to achieve better
signal integrity and avoid signal reflection.