參數(shù)資料
型號(hào): MPC9350D
廠商: Motorola, Inc.
英文描述: LOW VOLTAGE PLL CLOCK DRIVER
中文描述: 低壓PLL時(shí)鐘驅(qū)動(dòng)器
文件頁數(shù): 8/12頁
文件大?。?/td> 282K
代理商: MPC9350D
MPC9350
MOTOROLA
TIMING SOLUTIONS
The waveform plots in Figure 5. “Single versus Dual Line
Termination Waveforms” show the simulation results of an
output driving a single line versus two lines. In both cases the
drive capability of the MPC9350 output buffer is more than
sufficient to drive 50
transmission lines on the incident edge.
Note from the delay measurements in the simulations a delta
of only 43ps exists between the two differently loaded outputs.
This suggests that the dual line driving need not be used
exclusively to maintain the tight output-to-output skew of the
MPC9350. The output waveform in Figure 5. “Single versus
Dual Line Termination Waveforms” shows a step in the
waveform, this step is caused by the impedance mismatch
seen looking into the driver. The parallel combination of the
36
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:
VL = VS ( Z0
÷
(RS+R0 +Z0))
Z0 = 50
|| 50
RS = 36
|| 36
R0 = 17
VL = 3.0 ( 25
÷
(18+17+25)
= 1.25V
At the load end the voltage will double, due to the near unity
reflection coefficient, to 2.5V. It will then increment towards the
quiescent 3.0V in steps separated by one round trip delay (in
this case 4.0ns).
Figure 5. Single versus Dual Waveforms
TIME (nS)
V
3.0
2.5
2.0
1.5
1.0
0.5
0
2
4
6
8
10
12
14
OutB
tD = 3.9386
OutA
tD = 3.8956
In
Since this step is well above the threshold region it will not
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. “Optimized Dual Line Termination”
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.
Figure 6. Optimized Dual Line Termination
14
MPC9350
OUTPUT
BUFFER
RS = 22
ZO = 50
RS = 22
ZO = 50
14
+ 22
22
= 50
50
25
= 25
F
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
n
.
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