HP 54753A User Manual page 248

Table 11-3
Maximum Open Line Length for MECL III, MECL 10H209 (Gate Rise Time 1.1 ns)
Z
(OHMS)
o
MICROSTRIP
50
(Propagation
68
Delay 0.148 ns/in.)
75
82
90
100
STRIPLINE
50
(Propagation
68
Delay 0.188 ns/in.)
75
82
90
100
BACKPLANE 100
(Propagation
140
Delay 0.140 ns/in.)
180
Transmission Line Theory Applied to Digital Systems
Signal Propagation Delay for Microstrip and Strip Lines with Distributed or Lumped Loads
FANOUT = 1 FANOUT = 2
(3.3pF) (6.6pF)
l (IN) l
MAX MAX
1.6
1.4
1.3
1.2
1.1
1.0
1.2
1.1
1.0
0.9
0.9
0.8
1.1
0.8
0.6
The maximum line lengths are also given for various characteristic impedances
in the backplane. The characteristic impedance of the backplane should be
between 100 Ω and 180 Ω if a ground screen is used. For MECL 10K from
Table 11-1, 5.9 inches of open backplane wiring can be driven for a fanout of one.
It should be remembered that these line lengths are based on 100 mV maximum
undershoot, and are not absolute maximum lengths with which MECL circuits
will operate. It is possible to use longer unterminated lines than shown — the
tradeoff being an associated loss of noise immunity due to increased ringing.
11-20
FANOUT = 4
(13.2pF)
(IN) l (IN)
MAX
1.1 0.7
0.8 0.5
0.8 0.4
0.7 0.4
0.6 0.3
0.5 0.2
0.8 0.6
0.7 0.4
0.6 0.3
0.6 0.3
0.5 0.2
0.4 0.2
0.6 0.2
0.3 0.0
0.2 0.0
FANOUT = 8
(26.4pF)
l (IN)
MAX
0.6
0.4
0.3
0.2
0.2
0.1
0.5
0.3
0.2
0.2
0.1
0.1
0.1
0.0
0.0