Printed Circuit Board - Agilent Technologies 93000 SOC Series Training Manual

Lesson 2 – DUT Board Design Considerations
2-4

Printed Circuit Board

To run the same application on multiple testers for production tests, the
DUT board is developed as a printed circuit board (PCB).
As the operation rate of a mixed-signal device increases, application
engineers who develop test circuits need to be skilled not only in schematic
design but also in printed circuit board design. This is because traces on
the PCB at high frequency generate physical effects (reflection, crosstalk,
and so on) that are not represented in the schematic.
Characteristic Impedance
According to the transmission line theory, if the characteristic impedance
of a trace does not match the termination impedance and if a high-
frequency signal is transmitted in the line, a reflection will occur for the
signal. To measure a high-frequency signal accurately or to force a high-
frequency signal accurately, the transmission line must be designed to
match the termination impedance.
Hence, a microstrip line and strip line are used because their impedance
can be controlled by changing the thickness, width, and height above the
ground plane.
The following figure shows the model of a microstrip line:
t
Characteristic Impedance:
Zo =
Microstrip Line Model
where Er means the relative dielectric constant of the board material.
The following figure shows the model of a strip line:
536
W
Dielectric
Ground Plane
87 5.98*h
ln
0.8*w + t
Er + 1.41
h