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參數資料
| 型號： | AD8178-EVALZ1 |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | 450 MHz, Triple 16 】 5 Video Crosspoint Switch |
| 中文描述： | 450兆赫，三16】5視頻交叉點開關 |
| 文件頁數： | 34/40頁 |
| 文件大?。?/td> | 545K |
| 代理商： | AD8178-EVALZ1 |
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AD8178
many sources of crosstalk either destructively cancel, or are
common mode to, the signal and can be rejected by a differential
receiver.
Areas of Crosstalk
A practical AD8178 circuit must be mounted to an actual circuit
board to connect it to power supplies and measurement equipment.
Great care has been taken to create an evaluation board (available
upon request) that adds minimum crosstalk to the intrinsic device.
This, however, raises the issue that system crosstalk is a combi-
nation of the intrinsic crosstalk of the devices, in addition to the
circuit board to which they are mounted. It is important to try
to separate these two areas when attempting to minimize the
effect of crosstalk.
In addition, crosstalk can occur among the inputs to a crosspoint
and among the outputs. It can also occur from input to output.
In the following sections, techniques are discussed for diagnosing
which part of a system is contributing to crosstalk.
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 decibels
(dB) down from the magnitude of the test signal. The crosstalk
is expressed by
Rev. 0 | Page 34 of 40
=
)
(
)
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 × 5 matrix
of the AD8178, note the number of crosstalk terms that can be
considered for a single channel, for example, Input Channel
INPUT0. INPUT0 is programmed to connect to one of the
AD8178 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. Next, 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
can 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 measurement
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 astro-
nomical proportions. If a larger crosspoint array of multiple
AD8178 devices 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 it 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
AD8178, 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 it 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 AD8178 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 OUTPUT2 (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 OUTPUT2 disabled. Because grounded INPUT7
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| AD817AN | 功能描述:IC OPAMP HS LP 8-DIP RoHS:否 類別:集成電路 (IC) >> 線性 - 放大器 - 視頻放大器和頻緩沖器 系列:- 產品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:50 系列:- 應用:TFT-LCD 面板：VCOM 驅動器 輸出類型:滿擺幅 電路數:1 -3db帶寬:35MHz 轉換速率:40 V/µs 電流 - 電源:3.7mA 電流 - 輸出 / 通道:1.3A 電壓 - 電源，單路/雙路(±):9 V ~ 20 V，±4.5 V ~ 10 V 安裝類型:表面貼裝 封裝/外殼:8-TSSOP，8-MSOP（0.118"，3.00mm 寬）裸露焊盤 供應商設備封裝:8-uMax-EP 包裝:管件 |
| AD817AN | 制造商:Analog Devices 功能描述:SEMICONDUCTORSLINEAR |
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