Digital Signal Processing Reference
In-Depth Information
U1
U2
U3
U4
U5
U6
U7
U8
U9
U10
Figure 12.7
Circuit board artwork showing point-to-point topology from U1 to U4; single load
point-to-point from U2 to U3 and U5 - U6; multidrop from U7 to U8 through U10.
rows. In that case
T
1 is long enough to escape the pin field and to place the signal
in an open area where
R
s
can be mounted.
In lower-density boards the pin escape trace
T
1 is often routed as microstrip,
but high-performance, high-density boards will frequently escape with stripline. In
either case, the impedance of
T
1 (
Z
o
1
) is often not the same as that of
T
2 (
Z
o
2
). If
T
1 is too long, its impedance will determine the current launched by the driver and
reflections will occur even if
R
s
properly matches
T
2. For this reason the length of
T
1 should always be short compared to the signal rise time, and it should always
be less than the length of
T
2.
