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參數資料
| 型號： | AD8175 |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | Video Crosspoint Switch |
| 中文描述： | 視頻交叉點開關 |
| 文件頁數： | 32/40頁 |
| 文件大小： | 533K |
| 代理商： | AD8175 |
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AD8175
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 AD8175 taken with single-ended output
appears to have a gain of +1.
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 AD8175 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
Rev. 0 | Page 32 of 40
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 AD8175
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 this
error. This distorts the output signal from the ideal response
compared to the case when the two outputs are balanced.
Decoupling
The signal path of the AD8175 is based on high open-loop gain
amplifiers with negative feedback. Dominant-pole compensation
is used on-chip to stabilize these amplifiers over the range of
expected applied swing and load conditions. To guarantee this
designed stability, proper supply decoupling is necessary with
respect to both the differential control loops and the common-
mode control loops of the signal path. Signal-generated
currents must return to their sources through low impedance
paths at all frequencies in which there is still loop gain (up to
700 MHz at a minimum).
The signal path compensation capacitors in the AD8175 are
connected to the VNEG supply. At high frequencies, this limits
the power supply rejection ratio (PSRR) from the VNEG supply
to a lower value than that from the VPOS supply. If given a
choice, an application board should be designed such that the
VNEG power is supplied from a low inductance plane, subject
to a least amount of noise.
VOCM_CMENCON and VOCM_CMENCOFF are high speed
common-mode control loops of all output drivers. In the single-
ended output sense, there is no rejection from noise on these
inputs to the outputs. For this reason, care must be taken to
produce low noise sources over the entire range of frequencies
of interest. This is not only important to single-ended
operation, but to differential operation, as there is a common-
mode-to-differential gain conversion that becomes greater at
higher frequencies.
VOCM_CMENCON and VOCM_CMENCOFF are internally
buffered to prevent transient currents from flowing into or out
of these inputs and becoming sources of crosstalk, by acting on
their respective source impedances.
相關PDF資料 |
PDF描述 |
|---|---|
| AD8175ABPZ | Video Crosspoint Switch |
| AD8175-EVALZ | Video Crosspoint Switch |
| AD8176-EVAL | 475 MHz, Triple 16 】 9 Video Crosspoint Switch |
| AD8176 | 475 MHz, Triple 16 】 9 Video Crosspoint Switch |
| AD8176ABPZ | 475 MHz, Triple 16 】 9 Video Crosspoint Switch |
相關代理商/技術參數 |
參數描述 |
|---|---|
| AD8175ABPZ | 功能描述:IC CROSSPOINT SWITCH TRPL 676BGA 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:- 應用說明:Ultrasound Imaging Systems Application Note 產品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:250 系列:- 功能:開關 電路:單刀單擲 導通狀態電阻:48 歐姆 電壓電源:單電源 電壓 - 電源，單路/雙路(±):2.7 V ~ 5.5 V 電流 - 電源:5µA 工作溫度:0°C ~ 70°C 安裝類型:表面貼裝 封裝/外殼:48-LQFP 供應商設備封裝:48-LQFP（7x7） 包裝:托盤 |
| AD8175-EVALZ | 制造商:AD 制造商全稱:Analog Devices 功能描述:Video Crosspoint Switch |
| AD8176 | 制造商:AD 制造商全稱:Analog Devices 功能描述:475 MHz, Triple 16 】 9 Video Crosspoint Switch |
| AD8176ABPZ | 功能描述:IC VIDEO CROSSPOINT SWIT 676BGA 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，FCBGA 供應商設備封裝:7-覆晶 包裝:帶卷 (TR) |
| AD8176-EVAL | 制造商:AD 制造商全稱:Analog Devices 功能描述:475 MHz, Triple 16 】 9 Video Crosspoint Switch |
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