mpc904 Freescale Semiconductor, Inc, mpc904 Datasheet - Page 5

• Manufacturer Part Number: mpc904
• Description: Mpc903 1 6 Pci Clock Generator/ Fanout Buffer
• Manufacturer: Freescale Semiconductor, Inc

driving need not be used exclusively to maintain the tight
output–to–output skew of the MPC903. The output waveform
in Figure 5 shows a step in the waveform, this step is caused
by the impedance mismatch seen looking into the driver. The
parallel combination of the 43Ω series resistor plus the output
impedance does not match the parallel combination of the
line impedances. The voltage wave launched down the two
lines will equal:
unity reflection coefficient, to 2.8V. It will then increment
towards the quiescent 3.0V in steps separated by one round
trip delay (in this case 4.0ns).
TIMING SOLUTIONS
BR1333 — REV 5
At the load end the voltage will double, due to the near
3.0
2.5
2.0
1.5
1.0
0.5
VL = VS ( Zo / Rs + Ro +Zo) = 3.0 (25/53.5) = 1.40V
0
Figure 5. Single versus Dual Waveforms
t D = 3.8956
2
In
OutA
4
6
TIME (nS)
t D = 3.9386
OutB
8
10
12
14
5
cause any false clock triggering, however designers may be
uncomfortable with unwanted reflections on the line. To
better match the impedances when driving multiple lines the
situation in Figure 6 should be used. In this case the series
terminating resistors are reduced such that when the parallel
combination is added to the output buffer impedance the line
impedance is perfectly matched.
engineers who want to simulate their specific interconnect
schemes. In addition IV characteristics are in the process of
being generated to support the other board level simulators in
general use.
Since this step is well above the threshold region it will not
SPICE level output buffer models are available for
Figure 6. Optimized Dual Line Termination
OUTPUT
MPC903
BUFFER
7Ω
7Ω + 36Ω
MPC903 MPC904 MPC905
R S = 36Ω
R S = 36Ω
25Ω = 25Ω
k
36Ω = 50Ω
Z O = 50Ω
Z O = 50Ω
k
50Ω
MOTOROLA