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| 型號(hào)： | AD8176-EVAL |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | 475 MHz, Triple 16 】 9 Video Crosspoint Switch |
| 中文描述： | 475兆赫，三16】9視頻交叉點(diǎn)開關(guān) |
| 文件頁(yè)數(shù)： | 26/32頁(yè) |
| 文件大小： | 489K |
| 代理商： | AD8176-EVAL |
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AD8176
Preliminary Technical Data
Whenever a differential output is used single-ended, it is
desirable to terminate the used single-ended output with a
series resistor, as well as to place a resistor on the unused output
to match the load seen by the used output.
When disabled, the outputs float to midsupply. A small current
is required to drive the outputs away from their midsupply
state. This current is easily provided by an AD8176 output (in
its enabled state) bussed together with the disabled output.
Exceeding the allowed output voltage range may saturate
internal nodes in the disabled output, and consequently an
increase in disabled output current may be observed.
Single-Ended Output
Usage
The AD8176 output pairs can be used single-ended, taking only
one output and not using the second. This is often desired to
reduce the routing complexity in the design, or because a
single-ended load is being driven directly. This mode of
operation produces good results, but has some shortcomings
when compared to taking the output differentially. When
observing the single-ended output, noise that is common to
both outputs appears in the output signal.
When observing the output single-ended, the distribution of
offset voltages will appear greater. In the differential case, the
difference between the outputs when the difference between the
inputs is zero is a small differential offset. This offset is created
from mismatches in devices in the signal path. In the single-
ended case, this differential offset is still observed, but an
additional offset component is also relevant. This additional
component is the common-mode offset, which is the difference
between the average of the outputs and the output common-
mode reference. This offset is created by mismatches that affect
the signal path in a common-mode manner. A differential
receiver rejects this common-mode offset voltage, but in the
single-ended case, this offset is observed with respect to the
signal ground. The single-ended output sums half the
differential offset voltage and all of the common-mode offset
voltage for a net increase in observed offset.
Single-Ended Gain
The AD8176 operates as a closed-loop differential amplifier.
The primary control loop forces the difference between the
output terminals to be a ratio of the difference between the
input terminals. One output increases in voltage, while the
other decreases an equal amount to make the total output
voltage difference correct. The average of these output voltages
is forced to the voltage on the common-mode reference
terminal (VOCM_CMENCOFF or VOCM_CMENCON) by a
second control loop. If only one output terminal is observed
with respect to the common-mode reference terminal, only half
of the difference voltage will be observed. This implies that
when using only one output of the device, half of the differential
gain is observed. An AD8176 taken with single-ended output
appears to have a gain of +1.
Rev. PrA | Page 26 of 32
It is important to note that all considerations applying to the
used output phase regarding output voltage headroom, apply
unchanged to the complement output phase even if this is not
actually used.
Termination
When operating the AD8176 with a single-ended output, the
preferred output termination scheme is to refer the load to the
output common-mode. A series-termination can be used, at an
additional cost of one half the signal gain.
In single-ended output operation, the complementary phase of
the output is not used, and may or may not be terminated
locally. Although the unused output can be floated to reduce
power dissipation, there are several reasons for terminating the
unused output with a load resistance matched to the load on the
signal output.
One component of crosstalk is magnetic coupling by mutual
inductance between output package traces and bond wires that
carry load current. In a differential design, there is coupling
from one pair of outputs to other adjacent pairs of outputs. The
differential nature of the output signal simultaneously drives the
coupling field in one direction for one phase of the output, and
in an opposite direction for the other phase of the output. These
magnetic fields do not couple equally into adjacent output pairs
due to different proximities, but they do destructively cancel the
crosstalk to some extent. If the load current in each output is
equal, this cancellation will be greater and less adjacent
crosstalk will be observed (regardless of whether the second
output is actually being used).
A second benefit of balancing the output loads in a differential
pair is to reduce fluctuations in current requirements from the
power supply. In single-ended loads, the load currents alternate
from the positive supply to the negative supply. This creates a
parasitic signal voltage in the supply pins due to the finite
resistance and inductance of the supplies. This supply
fluctuation appears as crosstalk in all outputs, attenuated by the
power supply rejection ratio (PSRR) of the device. At low
frequencies, this is a negligible component of crosstalk, but
PSRR falls off as frequency increases. With differential,
balanced loads, as one output draws current from the positive
supply, the other output draws current from the negative supply.
When the phase alternates, the first output draws current from
the negative supply and the second from the positive supply.
The effect is that a more constant current is drawn from each
supply, such that the crosstalk-inducing supply fluctuation is
minimized.
A third benefit of driving balanced loads can be seen if one
considers that the output pulse response changes as load
changes. The differential signal control loop in the AD8176
forces the difference of the outputs to be a fixed ratio to the
difference of the inputs. If the two output responses are
different due to loading, this creates a difference that the control
loop sees as signal response error, and it will attempt to correct
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| AD8176 | 475 MHz, Triple 16 】 9 Video Crosspoint Switch |
| AD8176ABPZ | 475 MHz, Triple 16 】 9 Video Crosspoint Switch |
| AD8178 | 450 MHz, Triple 16 】 5 Video Crosspoint Switch |
| AD8178ABPZ1 | 450 MHz, Triple 16 】 5 Video Crosspoint Switch |
| AD8178-EVALZ1 | 450 MHz, Triple 16 】 5 Video Crosspoint Switch |
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| 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(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) |
| 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 |
| AD8178ABPZ | 功能描述:IC VIDEO CROSSPOINT SWIT 676BGA 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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