MPC9893 查看數據表（PDF） - Motorola => Freescale
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MPC9893 Datasheet PDF : 16 Pages
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Freescale Semiconductor, Inc.
MPC9893
feedback divider result in lower I/O jitter than the jitter limits in
the AC characterisitics (table 8 on page 6). When calculating
the part--to--part skew, Table 11 “Internal VCO frequency
fVCO” should be used to determine the actual VCO
frequency, then use Figure 5 “Max. I/O Phase Jitter versus
VCO Frequency” to determine the maximum I/O jitter for the
specific VCO frequency and divider configuration. In above
example calculation, the internal VCO frequency of 400 MHz
corresponds to a maximum I/O jitter of 30 ps (RMS).
Table 11: Internal VCO frequency fVCO
MPC9893
Configuration
fVCO
PLL feedback
divider FB
M1H, M12H, M2H, M22H
4 * fref
4
M3, M32
6 * fref
6
M1M, M12M, M2M,
8 * fref
8
M22M, M4, M42
M1L, M12L, M8, M82
16 * fref
16
Figure 5. Max. I/O Phase Jitter versus VCO Frequency
The cycle--to--cycle jitter and period jitter of the MPC9893
depend on the output configuration and on the frequency of
the internal VCO. Using the outputs of bank A and bank B at
the same frequency (FSEL3=0) results in a lower jitter than
the split output frequency configuration (FSEL3=1). The jitter
also decreases with an increasing internal VCO frequency.
Figures 4 to 6 represent the maximum jitter of the MPC9893.
Figure 7. Max. Period Jitter versus VCO Frequency
Driving Transmission Lines
The MPC9893 clock driver was designed to drive high
speed signals in a terminated transmission line environment.
To provide the optimum flexibility to the user the output
drivers were designed to exhibit the lowest impedance
possible. With an output impedance of less than 20Ω the
drivers can drive either parallel or series terminated
transmission lines. For more information on transmission
lines the reader is referred to Motorola application note
AN1091. In most high performance clock networks
point-to-point distribution of signals is the method of choice.
In a point-to-point scheme either series terminated or parallel
terminated transmission lines can be used. The parallel
technique terminates the signal at the end of the line with a
50Ω resistance to VCC÷2.
This technique draws a fairly high level of DC current and
thus only a single terminated line can be driven by each
output of the MPC9893 clock driver. For the series terminated
case however there is no DC current draw, thus the outputs
can drive multiple series terminated lines. Figure 8. “Single
versus Dual Transmission Lines” illustrates an output driving
a single series terminated line versus two series terminated
lines in parallel. When taken to its extreme the fanout of the
MPC9893 clock driver is effectively doubled due to its
capability to drive multiple lines.
MPC9893
OUTPUT
BUFFER
IN
14Ω
RS = 36Ω
ZO = 50Ω
OutA
Figure 6. Max. Cycle--to--Cycle Jitter versus VCO
Frequency
MPC9893
OUTPUT
BUFFER
IN
14Ω
RS = 36Ω
ZO = 50Ω
RS = 36Ω
ZO = 50Ω
OutB0
OutB1
Figure 8. Single versus Dual Transmission Lines
TIMING SOLUTIONS
For More Informa9tion On This Product,
Go to: www.freescale.com
MOTOROLA
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