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參數(shù)資料
| 型號： | AD8108AST |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | 運動控制電子 |
| 英文描述： | 325 MHz, 8 x 8 Buffered Video Crosspoint Switches |
| 中文描述： | 8-CHANNEL, CROSS POINT SWITCH, PQFP80 |
| 封裝： | 12 X 12 MM, PLASTIC, MO-026BDD, LQFP-80 |
| 文件頁數(shù)： | 18/28頁 |
| 文件大?。?/td> | 434K |
| 代理商： | AD8108AST |
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AD8108/AD8109
–18–
REV. 0
Some systems use twisted-pair wiring to carry video signals.
T hese systems utilize differential signals and can lower costs
because they use lower cost cables, connectors and termination
methods. T hey also have the ability to lower crosstalk and reject
common-mode signals, which can be important for equipment
that operates in noisy environments or where common-mode
voltages are present between transmitting and receiving equipment.
In such systems, the video signals are differential; there is a
positive and negative (or inverted) version of the signals. T hese
complementary signals are transmitted onto each of the two
wires of the twisted pair, yielding a first order zero common-
mode signal. At the receive end, the signals are differentially
received and converted back into a single-ended signal.
When switching these differential signals, two channels are
required in the switching element to handle the two differential
signals that make up the video channel. T hus, one differential
video channel is assigned to a pair of crosspoint channels, both
input and output. For a single AD8108/AD8109, four differen-
tial video channels can be assigned to the eight inputs and eight
outputs. T his will effectively form a 4
×
4 differential crosspoint
switch.
Programming such a device will require that inputs and outputs
be programmed in pairs. T his information can be deduced by
inspection of the programming format of the AD8108/AD8109
and the requirements of the system.
T here are other analog video formats requiring more than one
analog circuit per video channel. One two-circuit format that is
commonly being used in systems such as satellite T V, digital
cable boxes and higher quality VCRs, is called S-video or Y/C
video. T his format carries the brightness (luminance or Y) por-
tion of the video signal on one channel and the color (chromi-
nance, chroma or C) on a second channel.
Since S-video also uses two separate circuits for one video chan-
nel, creating a crosspoint system requires assigning one video
channel to two crosspoint channels as in the case of a differen-
tial video system. Aside from the nature of the video format,
other aspects of these two systems will be the same.
T here are yet other video formats using three channels to carry
the video information. Video cameras produce RGB (red, green,
blue) directly from the image sensors. RGB is also the usual
format used by computers internally for graphics. RGB can also
be converted to Y, R–Y, B–Y format, sometimes called YUV
format. T hese three-circuit, video standards are referred to as
component analog video.
T he component video standards require three crosspoint chan-
nels per video channel to handle the switching function. In a
fashion similar to the two-circuit video formats, the inputs and
outputs are assigned in groups of three and the appropriate logic
programming is performed to route the video signals.
C ROSST ALK
Many systems, such as broadcast video, that handle numerous
analog signal channels have strict requirements for keeping the
various signals from influencing any of the others in the system.
Crosstalk is the term used to describe the coupling of the signals
of other nearby channels to a given channel.
When there are many signals in close proximity in a system, as
will undoubtedly be the case in a system that uses the AD8108/
AD8109, the crosstalk issues can be quite complex. A good
understanding of the nature of crosstalk and some definition of
terms is required in order to specify a system that uses one or
more AD8108/AD8109s.
T Y PE S OF CROSST ALK
Crosstalk can be propagated by means of any of three methods.
T hese fall into the categories of electric field, magnetic field and
sharing of common impedances. T his section will explain these
effects.
Every conductor can be both a radiator of electric fields and a
receiver of electric fields. T he electric field crosstalk mechanism
occurs when the electric field created by the transmitter propa-
gates across a stray capacitance (e.g., free space) and couples
with the receiver and induces a voltage. T his voltage is an un-
wanted crosstalk signal in any channel that receives it.
Currents flowing in conductors create magnetic fields that circu-
late around the currents. T hese magnetic fields will then gener-
ate voltages in any other conductors whose paths they link. T he
undesired induced voltages in these other channels are crosstalk
signals. T he channels that crosstalk can be said to have a mutual
inductance that couples signals from one channel to another.
T he power supplies, grounds and other signal return paths of a
multichannel system are generally shared by the various chan-
nels. When a current from one channel flows in one of these
paths, a voltage that is developed across the impedance becomes
an input crosstalk signal for other channels that share the com-
mon impedance.
All these sources of crosstalk are vector quantities, so the
magnitudes cannot simply be added together to obtain the
total crosstalk. In fact, there are conditions where driving addi-
tional circuits in parallel in a given configuration can actually
reduce the crosstalk.
Areas of Crosstalk
For a practical AD8108/AD8109 circuit, it is required that it be
mounted to some sort of circuit board in order to connect it to
power supplies and measurement equipment. Great care has
been taken to create a characterization board (also available as
an evaluation board) that adds minimum crosstalk to the intrin-
sic device. T his, however, raises the issue that a system’s crosstalk
is a combination of the intrinsic crosstalk of the devices in addi-
tion to the circuit board to which they are mounted. It is impor-
tant to try to separate these two areas of crosstalk when attempting
to minimize its effect.
In addition, crosstalk can occur among the inputs to a cross-
point and among the outputs. It can also occur from input to
output. T echniques will be 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 chan-
nels and measuring the relative strength of that signal on a de-
sired selected channel. T he measurement is usually expressed as
dB down from the magnitude of the test signal. T he crosstalk is
expressed by:
|
X T
| = 20 log
10
(
Asel
(
s
)/
Atest
(
s
))
相關PDF資料 |
PDF描述 |
|---|---|
| AD8109 | 325 MHz, 8 x 8 Buffered Video Crosspoint Switches |
| AD8109AST | ECONOLINE: REC2.2-S_DRW(Z)/H* - 2.2W DIP Package- 1kVDC Isolation- Regulated Output- 4.5-9V, 9-18V, 18-36V, 36-72V Wide Input Range 2 : 1- UL94V-0 Package Material- Continuous Short Circiut Protection- Cost Effective- 100% Burned In- Efficiency to 84% |
| AD8109* | 325 MHz. 8 3 8 Buffered Video Crosspoint Switches |
| AD8109-EB | 325 MHz, 8 x 8 Buffered Video Crosspoint Switches |
| AD810AN | Low Power Video Op Amp with Disable |
相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| AD8108ASTZ | 功能描述:IC VIDEO CROSSPOINT SWIT 80LQFP 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(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 供應商設備封裝:7-覆晶 包裝:帶卷 (TR) |
| AD8108ASTZ | 制造商:Analog Devices 功能描述:IC SWITCH VIDEO |
| AD8108ASTZ2 | 制造商:AD 制造商全稱:Analog Devices 功能描述:325 MHz, 8 ?? 8 Buffered Video Crosspoint Switches |
| AD8108EB | 制造商:Analog Devices 功能描述: |
| AD8108-EB | 制造商:Analog Devices 功能描述:Evaluation Board For IC Video Crosspt 325MHz 8X8 制造商:Analog Devices 功能描述:VID CROSSPT 325MHZ 8X8 - Bulk |
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