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参数资料
| 型号： | MPC9658ACR2 |
| 厂商： | FREESCALE SEMICONDUCTOR INC |
| 元件分类： | 时钟及定时 |
| 英文描述： | 9658 SERIES, PLL BASED CLOCK DRIVER, 10 TRUE OUTPUT(S), 0 INVERTED OUTPUT(S), PQFP32 |
| 封装： | 7 X 7 MM, LEAD FREE, LQFP-32 |
| 文件页数： | 10/12页 |
| 文件大小： | 344K |
| 代理商： | MPC9658ACR2 |
Advanced Clock Drivers Device Data
Freescale Semiconductor
7
MPC9658
Calculation of Part-to-Part Skew
The MPC9658 zero delay buffer supports applications
where critical clock signal timing can be maintained across
several devices. If the reference clock inputs of two or more
MPC9658 are connected together, the maximum overall
timing uncertainty from the common PCLK input to any output
is:
tSK(PP) = t() + tSK(O) + tPD, LINE(FB) + tJIT() CF
This maximum timing uncertainty consist of four
components: static phase offset, output skew, feedback
board trace delay, and I/O (phase) jitter:
Figure 4. MPC9658 Max. Device-to-Device Skew
Due to the statistical nature of I/O jitter a RMS value (1
σ)
is specified. I/O jitter numbers for other confidence factors
(CF) can be derived from Table 8.
The feedback trace delay is determined by the board
layout and can be used to fine-tune the effective delay
through each device. In the following example calculation a
I/O jitter confidence factor of 99.7% (
± 3σ) is assumed,
resulting in a worst case timing uncertainty from input to any
output of –214 ps to 224 ps relative to PCKL (fREF = 100 MHz,
FB = 4, tjit() = 8 ps RMS at fVCO = 400 MHz):
tSK(PP) = [–70ps...80ps] + [–120ps...120ps] +
[(8ps
–3)...(8ps 3)] + tPD, LINE(FB)
tSK(PP) = [–214ps...224ps] + tPD, LINE(FB)
Due to the frequency dependence of the I/O jitter, Figure 5
can be used for a more precise timing performance analysis.
Figure 5. Max. I/O Jitter versus Frequency
Driving Transmission Lines
The MPC9658 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 20
the
drivers can drive either parallel or series terminated
transmission lines. For more information on transmission
lines, the reader is referred to Freescale Semiconductor
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 50
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 MPC9658 clock driver. However, for the series
terminated case there is no DC current draw, thus the
outputs can drive multiple series terminated lines. Figure 6
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 MPC9658 clock driver is
effectively doubled due to its capability to drive multiple lines.
Table 8. Confidence Factor CF
CF
Probability of clock edge within the distribution
± 1σ
0.68268948
± 2σ
0.95449988
± 3σ
0.99730007
± 4σ
0.99993663
± 5σ
0.99999943
± 6σ
0.99999999
tPD,LINE(FB)
tJIT()
+tSK(O)
—t()
+t()
tJIT()
+tSK(O)
tSK(PP)
Max. skew
TCLKCommon
QFBDevice 1
Any QDevice 1
QFBDevice2
Any QDevice 2
FCO Frequency [MHz]
200
250
300
350
400
450
500
FB = 4
FB = 2
0
15
10
5
20
t jit(
f)[p
s]
R
M
S
I/O Phase Jitter versus Frequency
Parameter: PLL Feedback Divider FB
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