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參數(shù)資料
| 型號(hào)： | 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(diǎn)開關(guān)視頻交叉點(diǎn)開關(guān) |
| 文件頁數(shù)： | 27/32頁 |
| 文件大?。?/td> | 488K |
| 代理商： | AD8117 |
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Preliminary Technical Data
AD8117/AD8118
Input and Output Crosstalk
Rev. PrA | Page 27 of 32
Capacitive coupling is voltage-driven (dV/dt), but is generally a
constant ratio. Capacitive crosstalk is proportional to input or
output voltage, but this ratio is not reduced by simply reducing
signal swings. Attenuation factors must be changed by
changing impedances (lowering mutual capacitance), or
destructive canceling must be utilized by summing equal and
out of phase components. For high-input impedance devices
such as the AD8117/AD8118, capacitances generally dominate
input-generated crosstalk.
Inductive coupling is proportional to current (dI/dt), and will
often scale as a constant ratio with signal voltage, but will also
show a dependence on impedances (load current). Inductive
coupling can also be reduced by constructive canceling of equal
and out of phase fields. In the case of driving low-impedance
video loads, output inductances contribute highly to output
crosstalk.
The flexible programming capability of the AD8117/AD8118
can be used to diagnose whether crosstalk is occurring more on
the input side or the output side. Some examples are
illustrative. A given input pair (IN07 in the middle for this
example) can be programmed to drive OUT07 (also in the
middle). The inputs to IN07 are just terminated to ground (via
50 Ω
or 75 Ω) and no signal is applied.
All the other inputs are driven in parallel with the same test
signal (practically provided by a distribution amplifier), with all
other outputs except OUT07 disabled. Since grounded IN07 is
programmed to drive OUT07, no signal should be present. Any
signal that is present can be attributed to the other 15 hostile
input signals, because no other outputs are driven (they are all
disabled). Thus, this method measures the all-hostile input
contribution to crosstalk into IN07. Of course, the method can
be used for other input channels and combinations of hostile
inputs.
For output crosstalk measurement, a single input channel is
driven (IN00, for example) and all outputs other than a given
output (IN07 in the middle) are programmed to connect to
IN00. OUT07 is programmed to connect to IN15 (far away
from IN00), which is terminated to ground. Thus OUT07
should not have a signal present since it is listening to a quiet
input. Any signal measured at the OUT07 can be attributed to
the output crosstalk of the other 16 hostile outputs. Again, this
method can be modified to measure other channels and other
crosspoint matrix combinations.
Effect of Impedances on Crosstalk
The input side crosstalk can be influenced by the output
impedance of the sources that drive the inputs. The lower the
impedance of the drive source, the lower the magnitude of the
crosstalk. The dominant crosstalk mechanism on the input side
is capacitive coupling. The high impedance inputs do not have
significant current flow to create magnetically induced
crosstalk. However, significant current can flow through the
input termination resistors and the loops that drive them. Thus,
the PC board on the input side can contribute to magnetically
coupled crosstalk.
From a circuit standpoint, the input crosstalk mechanism looks
like a capacitor coupling to a resistive load. For low frequencies
the magnitude of the crosstalk will be given by
where
R
S
is the source resistance,
C
M
is the mutual capacitance
between the test signal circuit and the selected circuit, and
s
is
the Laplace transform variable.
From the equation it can be observed that this crosstalk
mechanism has a high-pass nature; it can also be minimized by
reducing the coupling capacitance of the input circuits and
lowering the output impedance of the drivers. If the input is
driven from a 75 Ω terminated cable, the input crosstalk can be
reduced by buffering this signal with a low output impedance
buffer.
On the output side, the crosstalk can be reduced by driving a
lighter load. Although the AD8117 is specified with excellent
differential gain and phase when driving a standard 150 Ω
video load, the crosstalk will be higher than the minimum
obtainable due to the high output currents. These currents will
induce crosstalk via the mutual inductance of the output pins
and bond wires of the AD8117.
From a circuit standpoint, this output crosstalk mechanism
looks like a transformer with a mutual inductance between the
windings that drives a load resistor. For low frequencies, the
magnitude of the crosstalk is given by
where
M
XY
is the mutual inductance of output X to output Y
and
R
L
is the load resistance on the measured output. This
crosstalk mechanism can be minimized by keeping the mutual
inductance low and increasing R
L
. The mutual inductance can
be kept low by increasing the spacing of the conductors and
minimizing their parallel length.
PCB Layout
Extreme care must be exercised to minimize additional
crosstalk generated by the system circuit board(s). The areas
|XT|
= 20 log
10
[(
R
S
C
M
)
×
s
]
|XT|
= 20 log
10
(
M
XY
×
s
/
R
L
)
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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(biāo)準(zhǔn)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(biāo)準(zhǔn)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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