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參數(shù)資料
| 型號： | AD8117 |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | Video Crosspoint Switch Video Crosspoint Switch |
| 中文描述： | 視頻交叉點開關(guān)視頻交叉點開關(guān) |
| 文件頁數(shù)： | 28/32頁 |
| 文件大小： | 488K |
| 代理商： | AD8117 |
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AD8117/AD8118
Preliminary Technical Data
that must be carefully detailed are grounding, shielding, signal
routing, and supply bypassing.
Rev. PrA | Page 28 of 32
The packaging of the AD8117/AD8118 is designed to help keep
the crosstalk to a minimum. On the BGA substrate, each pair is
carefully routed to predominately couple to each other, with
shielding traces separating adjacent signal pairs. The ball grid
array is arranged such that similar board routing can be
achieved. Only the outer two rows are used for signals, such
that vias can be used to take the input rows to a lower signal
plane if desired.
The input and output signals will have minimum crosstalk if
they are located between ground planes on layers above and
below, and separated by ground in between. Vias should be
located as close to the IC as possible to carry the inputs and
outputs to the inner layer. The input and output signals surface
at the input termination resistors and the output series back-
termination resistors. To the extent possible, these signals
should also be separated as soon as they emerge from the IC
package.
PCB Termination Layout
As frequencies of operation increase, the importance of proper
transmission line signal routing becomes more important. The
bandwidth of the AD8117/AD8118 is large enough that using
high impedance routing will not provide a flat in-band
frequency response for practical signal trace lengths. It is
necessary for the user to choose a characteristic impedance
suitable for the application and properly terminate the input
and output signals of the AD8117/AD8118. Traditionally,
video applications have used 75 Ω single-ended enviroments.
RF applications are generally 50 Ω single-ended (and board
manufacturers have the most experience with this application).
CAT-5 cabling is usually driven as differential pairs of 100 Ω
differential impedance.
For flexibility, the AD8117/AD8118 does not contain on-chip
termination resistors. This flexibility in application comes with
some board layout challenges. The distance between the
termination of the input transmission line and the
AD8117/AD8118 die is a high-impedance stub, and will cause
reflections of the input signal. With some simplification, it can
be shown that these reflections will cause peaking of the input
at regular intervals in frequency, dependent on the propagation
speed (
V
P
) of the signal in the choosen board material and the
distance (
d
) between the termination resistor and the
AD8117/AD8118. If the distance is great enough, these peaks
can occur in-band. In fact, practical experience shows that
these peaks are not high-
Q
, and should be pushed out to three
or four times the desired bandwidth in order to not have an
effect on the signal. For a board designer using FR4 (
V
P
= 144
× 10
6
m/s), this means the AD8117/AD8118 should be no more
than 1.5 cm after the termination resistors, and preferably
should be placed even closer. The BGA substrate routing inside
the AD8117/AD8118 is approximately 1 cm in length and adds
to the stub length, so 1.5 cm PCB routing equates to
d
= 2.5 × 10
–2
m in the calculations.
In some cases, it is difficult to place the termination close to the
AD8117/AD8118 due to space constraints, differential routing,
and large resistor footprints. A preferable solution in this case
is to maintain a controlled transmission line past the
AD8117/AD8118 inputs and terminate the end of the line.
This is known as fly-by termination. The input impedance of
the AD8117/AD8118 is large enough and stub length inside the
package is small enough that this works well in practice.
Implementation of fly-by input termination often includes
bringing the signal in on one routing layer, then passing
through a filled-via under the AD8117/AD8118 input ball, then
back out to termination on another signal layer. In this case,
care must be taken to tie the reference ground planes together
near the signal via if the signal layers are referenced to different
ground planes.
OPn
AD8117
ONn
IPn
INn
75
Figure 29. Fly-by Input Termination. Grounds for the two transmission lines
shown must be tied together close to the INn pin.
If multiple AD8117/AD8118 are to be driven in parallel, a fly-
by input termination scheme is very useful, but the distance
from each AD8117/AD8118 input to the driven input
transmission line is a stub that should be minimized in length
and parasitics using the discussed guidelines.
When driving the AD8117/AD8118 single-endedly, the
undriven input is often terminated with a resistance in order to
balance the input stage. It can be seen that by terminating the
undriven input with a resistor of one-half the characteristic
impedance, the input stage will be perfectly balanced (37.5 Ω,
for example, to balance the two parallel 75 Ω terminations on
the driven input). However, due to the feedback in the input
receiver, there is high-speed signal current leaving the undriven
input. In order to terminate this high-speed signal, proper
transmission-line techniques should be used. One solution is
f
peak
=
(2n + 1)V
P
4d
,
n
= {0, 1, 2, 3, …}
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| AD8117_07 | 制造商:AD 制造商全稱:Analog Devices 功能描述:600 MHz, 32 】 32 Buffered Analog Crosspoint Switch |
| AD8117ABPZ | 功能描述:IC CROSSPOINT SWIT 32X32 304BGA RoHS:是 類別:集成電路 (IC) >> 接口 - 模擬開關(guān)，多路復(fù)用器，多路分解器 系列:- 其它有關(guān)文件:STG4159 View All Specifications 標準包裝:5,000 系列:- 功能:開關(guān) 電路:1 x SPDT 導(dǎo)通狀態(tài)電阻:300 毫歐 電壓電源:雙電源 電壓 - 電源，單路/雙路(±):±1.65 V ~ 4.8 V 電流 - 電源:50nA 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:7-WFBGA，F(xiàn)CBGA 供應(yīng)商設(shè)備封裝:7-覆晶 包裝:帶卷 (TR) |
| AD8117-EVAL | 制造商:AD 制造商全稱:Analog Devices 功能描述:600 MHz, 32 】 32 Buffered Analog Crosspoint Switch |
| AD8118 | 制造商:AD 制造商全稱:Analog Devices 功能描述:600 MHz, 32 】 32 Buffered Analog Crosspoint Switch |
| AD8118ABPZ | 功能描述:IC CROSSPOINT SWIT 32X32 304BGA RoHS:是 類別:集成電路 (IC) >> 接口 - 模擬開關(guān)，多路復(fù)用器，多路分解器 系列:- 其它有關(guān)文件:STG4159 View All Specifications 標準包裝:5,000 系列:- 功能:開關(guān) 電路:1 x SPDT 導(dǎo)通狀態(tài)電阻:300 毫歐 電壓電源:雙電源 電壓 - 電源，單路/雙路(±):±1.65 V ~ 4.8 V 電流 - 電源:50nA 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:7-WFBGA，F(xiàn)CBGA 供應(yīng)商設(shè)備封裝:7-覆晶 包裝:帶卷 (TR) |
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