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參數(shù)資料
| 型號： | AD8117 |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | Video Crosspoint Switch Video Crosspoint Switch |
| 中文描述： | 視頻交叉點(diǎn)開關(guān)視頻交叉點(diǎn)開關(guān) |
| 文件頁數(shù)： | 23/32頁 |
| 文件大?。?/td> | 488K |
| 代理商： | AD8117 |
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Preliminary Technical Data
AD8117/AD8118
Rev. PrA | Page 23 of 32
Figure 25. Example of Back-Terminated Differential Load
Single-ended Output
Usage
The AD8117/AD8118 output pairs can be used single-endedly,
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 will produce 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.
This includes thermal noise in the chip biasing, as well as
crosstalk that coupled into the signal path. This component
noise and crosstalk is equal in both outputs, and as such can be
ignored by a differential receiver with high common-mode
rejection ratio. But when taking the output single-ended, this
noise is present with respect to the ground (or VOCM)
reference and is not rejected.
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 will be a small differential offset. This offset of
created from mismatches in components of the signal path
which must be corrected by the finite differential loop gain of
the device. 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 a difference between the average of the outputs
and the VOCM reference. This offset is created by mismatches
that affect the signal path in a common-mode manner, and is
corrected by the finite common-mode loop gain of the device.
A differential receiver would reject 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 gain in observed random offset.
Single-Ended Gain
The AD8117/AD8118 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 will increase in
voltage, while the other decreases an equal amount to make the
total difference correct. The average of these output voltages is
forced to the voltage on the VOCM terminal by a second
control loop. If only one output terminal is observed with
respect to the VOCM 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 will be
observed. An AD8117 taken with single-ended output will
appear to have a gain of +0.5. An AD8118 will be a single-
ended gain of +1.
This factor of one-half in the gain increases the noise of the
device when referred to the input, contributing to higher noise
specifications for single-ended output designs.
Termination
When operating the AD8117/AD8118 with a single-ended
output, the preferred output termination scheme is a resistor at
the load end to the VOCM voltage. A back-termination may be
used, at an additional cost of one half the signal gain.
In single-ended output operation, the second phase of the
output is not used, and may or may not be terminated locally.
Termination of the unused output is not necessary for proper
device operation, so total design power dissipation can be
reduced by floating this output. However, there are several
reasons for terminating the unused output with a load
resistance equal to 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 exactly equal 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 if 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.
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| AD8117_07 | 制造商:AD 制造商全稱:Analog Devices 功能描述:600 MHz, 32 】 32 Buffered Analog Crosspoint Switch |
| AD8117ABPZ | 功能描述:IC CROSSPOINT SWIT 32X32 304BGA 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) |
| AD8117-EVAL | 制造商:AD 制造商全稱:Analog Devices 功能描述:600 MHz, 32 】 32 Buffered Analog Crosspoint Switch |
| AD8118 | 制造商:AD 制造商全稱:Analog Devices 功能描述:600 MHz, 32 】 32 Buffered Analog Crosspoint Switch |
| AD8118ABPZ | 功能描述:IC CROSSPOINT SWIT 32X32 304BGA 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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