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參數資料
| 型號： | AD8176ABPZ |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | 運動控制電子 |
| 英文描述： | 475 MHz, Triple 16 】 9 Video Crosspoint Switch |
| 中文描述： | 16-CHANNEL, CROSS POINT SWITCH, PBGA676 |
| 封裝： | 27 X 27 MM, 1 MM PITCH, ROHS COMPLIANT, PLASTIC, MS-034AAL-1, BGA-676 |
| 文件頁數： | 29/32頁 |
| 文件大?。?/td> | 489K |
| 代理商： | AD8176ABPZ |
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Preliminary Technical Data
AD8176
Measuring Crosstalk
Crosstalk is measured by applying a signal to one or more
channels and measuring the relative strength of that signal on a
desired selected channel. The measurement is usually expressed
as dB down from the magnitude of the test signal. The crosstalk
is expressed by
Rev. PrA | Page 29 of 32
=
)
(
)
s
(
log
20
10
A
s
A
XT
TEST
SEL
(8)
where:
s
=
jω
is the Laplace transform variable
A
SEL
(
s
) is the amplitude of the crosstalk induced signal in the
selected channel
A
TEST
(
s
) is the amplitude of the test signal.
It can be seen that crosstalk is a function of frequency, but not a
function of the magnitude of the test signal (to first order). In
addition, the crosstalk signal has a phase relative to the test
signal associated with it.
A network analyzer is most commonly used to measure
crosstalk over a frequency range of interest. It can provide both
magnitude and phase information about the crosstalk signal.
As a crosspoint system or device grows larger, the number of
theoretical crosstalk combinations and permutations can
become extremely large. For example, in the case of the triple
16×9 matrix of the AD8176, we can look at the number of
crosstalk terms that can be considered for a single channel, say
input channel INPUT0. INPUT0 is programmed to connect to
one of the AD8176 outputs where the measurement can be made.
First, the crosstalk terms associated with driving a test signal
into each of the other 15 input channels can be measured one at
a time, while applying no signal to INPUT0. Then, the crosstalk
terms associated with driving a parallel test signal into all 15
other inputs can be measured two at a time in all possible
combinations, then three at a time, and so on, until, finally,
there is only one way to drive a test signal into all 15 other input
channels in parallel.
Each of these cases is legitimately different from the others and
might yield a unique value, depending on the resolution of the
measurement system, but it is hardly practical to measure all
these terms and then specify them. In addition, this describes
the crosstalk matrix for just one input channel. A similar
crosstalk matrix can be proposed for every other input. In
addition, if the possible combinations and permutations for
connecting inputs to the other outputs (not used for
measurement) are taken into consideration, the numbers rather
quickly grow to astronomical proportions. If a larger crosspoint
array of multiple AD8176s is constructed, the numbers grow
larger still.
Obviously, some subset of all these cases must be selected to be
used as a guide for a practical measure of crosstalk. One
common method is to measure all hostile crosstalk; this means
that the crosstalk to the selected channel is measured while all
other system channels are driven in parallel. In general, this
yields the worst crosstalk number, but this is not always the
case, due to the vector nature of the crosstalk signal.
Other useful crosstalk measurements are those created by one
nearest neighbor or by the two nearest neighbors on either side.
These crosstalk measurements are generally higher than those
of more distant channels, so they can serve as a worst-case
measure for any other one-channel or two-channel crosstalk
measurements.
Input and Output Crosstalk
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
AD8176, capacitances generally dominate input-generated
crosstalk.
Inductive coupling is proportional to current (dI/dt), and often
scales as a constant ratio with signal voltage, but also shows 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 AD8176 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 channel (INPUT7 roughly in the middle for this example)
can be programmed to drive OUTPUT4 (exactly in the middle).
The inputs to INPUT7 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 OUTPUT4 disabled. Since grounded
INPUT7 is programmed to drive OUTPUT4, 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 INPUT7. 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 (INPUT0, for example) and all outputs other than a
given output (OUTPUT4 in the middle) are programmed to
connect to INPUT0. OUTPUT4 is programmed to connect to
INPUT15 (far away from INPUT0), which is terminated to
ground. Thus, OUTPUT4 should not have a signal present since
it is listening to a quiet input. Any signal measured at the
OUTPUT4 can be attributed to the output crosstalk of the other
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相關代理商/技術參數 |
參數描述 |
|---|---|
| AD8176-EVAL | 制造商:AD 制造商全稱:Analog Devices 功能描述:475 MHz, Triple 16 】 9 Video Crosspoint Switch |
| AD8177 | 制造商:AD 制造商全稱:Analog Devices 功能描述:500 MHz, Triple 16 】 5 Video Crosspoint Switch |
| AD8177ABPZ | 功能描述:IC VIDEO CROSSPOINT SWIT 676BGA RoHS:是 類別:集成電路 (IC) >> 接口 - 模擬開關，多路復用器，多路分解器 系列:- 其它有關文件:STG4159 View All Specifications 標準包裝:5,000 系列:- 功能:開關 電路:1 x SPDT 導通狀態電阻: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，FCBGA 供應商設備封裝:7-覆晶 包裝:帶卷 (TR) |
| AD8177-EVALZ | 制造商:AD 制造商全稱:Analog Devices 功能描述:500 MHz, Triple 16 】 5 Video Crosspoint Switch |
| AD8178 | 制造商:AD 制造商全稱:Analog Devices 功能描述:450 MHz, Triple 16 】 5 Video Crosspoint Switch |
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