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參數(shù)資料
| 型號(hào)： | AD8187 |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | 運(yùn)動(dòng)控制電子 |
| 英文描述： | 480 MHz Single-Supply (5 V) Triple 2:1 Multiplexers |
| 中文描述： | TRIPLE 2-CHANNEL, SGL ENDED MULTIPLEXER, PDSO24 |
| 封裝： | TSSOP-24 |
| 文件頁(yè)數(shù)： | 16/20頁(yè) |
| 文件大小： | 474K |
| 代理商： | AD8187 |
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REV. A
–16–
AD8186/AD8187
A dc restore circuit using the AD8187 is shown in Figure 11.
Two separate sources of RGB video are ac-coupled to the
0.1
μ
F input capacitors of the AD8187. The input points of
the
AD8187 are switched to a 1.5 V reference by the ADG786,
which works in the following manner:
The SEL A/
B
signal selects the A or B inputs to the AD8187. It
also selects the switch positions in the ADG786 such that the
same selected inputs will be connected to V
REF
when
EN
is low.
During the horizontal interval, all of the RGB input signals are at
a flat black level. A logic signal that is low during
HSYNC
is
applied to the
EN
of the ADG786. This closes the switches
and
clamps the black level to 1.5 V. At all other times, the switches
are off and the node at the inputs to the AD8187 floats.
There are two considerations for sizing the input coupling capaci-
tors. One is the time constant during the H-pulse clamping. The
other is the droop associated with the capacitor discharge due to the
input bias current of the AD8187. For the former, it is better to
have a small capacitor; but for the latter, a larger capacitor is better.
The ON resistance of the ADG786 and the coupling capacitor
forms the time constant of the input clamp. The ADG786 ON
resistance is 5
max. With a 0.1
μ
F capacitor, a time constant
of 0.5
μ
s is created. Thus, a sync pulse of greater than 2.5
μ
s will
cause less than 1% error. This is not critical because the
black
level from successive lines is very close and the voltage
changes
little from line to line.
A rough approximation for the horizontal line time for a graphics
system is 30
μ
s. This will vary depending on the resolution and
the vertical rate. The coupling capacitor needs to hold the voltage
relatively constant during this time while the input bias current
of the AD8187 is discharging it.
The change in voltage is I
BIAS
times the line time divided by
the capacitance. With an I
BIAS
of 2.5
μ
A, a line time of 30
μ
s,
and a 0.1
μ
F coupling capacitor, the amount of droop is
0.75 mV. This is roughly 0.1% of the full video amplitude and
will not be observable in the video display.
High Speed Design Considerations
The AD8186/AD8187 are extremely high speed switching ampli-
fiers for routing the highest resolution graphic signals. Extra care
is required in the circuit design and layout to ensure that the full
resolution of the video is realized.
First, the board should have at least one layer of a solid ground
plane. Long signal paths should be referenced to a ground plane
as controlled-impedance traces. All bypass capacitors should be
very close to the pins of the part with absolutely minimum extra
circuit length in the path. It is also helpful to have a large V
CC
plane on a circuit board layer that is closely spaced to the ground
plane. This creates a low inductance interplane capacitance,
which is very helpful in supplying the fast transient currents that
the part demands during high resolution signal transitions.
Evaluation Board
An evaluation board has been designed and is offered for run-
ning the AD8186/AD8187 on a single supply. The inputs and
outputs
are ac-coupled and terminated with 75
resistors.
For the AD8187, a potentiometer is provided to allow setting
V
REF
at
any value between V
CC
and ground.
The logic control signals can be statically set by adding or
removing a jumper. If it is required to drive the logic pins
with a fast signal, an SMA connector can be used to deliver the
signal, and a place for a termination resistor is provided.
RED
GRN
BLU
IN2B
IN1B
IN0B
IN0A
REDA
IN1A
GRNA
IN2A
BLUA
V
REF
BLUB
GRNB
REDB
DV
CC
3V TO 5V
SEL A/
B
OE
2
OUT0
OUT1
OUT2
V
CC
5V
AD8187
2
2
S1A
S1B
S2A
S2B
S3A
S3B
ADG786
V
DD
5V
D1
D2
D3
GND
V
SS
LOGIC
EN
A0
A1
A2
HSYNC
2.4V MIN
0.8V MIN
V
REF
+
10 F
5V
3.48k
1.5k
1.5V
0.1 F
SEL A/
B
0.1 F
0.1 F
0.1 F
0.1 F
0.1 F
0.1 F
V
REF
V
EE
D
GND
Figure 11. AD8187 AC-Coupled with DC Restore
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| AD8187ARU | 制造商:Analog Devices 功能描述:Analog Multiplexer Triple 2:1 24-Pin TSSOP 制造商:Rochester Electronics LLC 功能描述:TSSOP TRIPLE 2:1 G=+2 SINGLE SUPPLY MUX - Bulk |
| AD8187ARU-REEL | 制造商:Analog Devices 功能描述:Analog Multiplexer Triple 2:1 24-Pin TSSOP T/R |
| AD8187ARU-REEL7 | 制造商:Analog Devices 功能描述:Analog Multiplexer Triple 2:1 24-Pin TSSOP T/R 制造商:Rochester Electronics LLC 功能描述:- Tape and Reel |
| AD8187ARUZ | 功能描述:IC MULTIPLEXER TRPL 2X1 24TSSOP 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) |
| AD8187ARUZ-REEL | 功能描述:IC MULTIPLEXER TRPL 2X1 24TSSOP 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:- 標(biāo)準(zhǔn)包裝:1,000 系列:- 功能:多路復(fù)用器 電路:1 x 4:1 導(dǎo)通狀態(tài)電阻:- 電壓電源:雙電源 電壓 - 電源，單路/雙路(±):±5V 電流 - 電源:7mA 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:16-SOIC（0.154"，3.90mm 寬） 供應(yīng)商設(shè)備封裝:16-SOIC 包裝:帶卷 (TR) |
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