參數(shù)資料
型號(hào)： AD8107ASTZ
廠商： Analog Devices Inc
文件頁(yè)數(shù)： 11/28頁(yè)
文件大?。?/td> 0K
描述： IC CROSSPOINT SWITCH 16X5 80LQFP
標(biāo)準(zhǔn)包裝： 1
功能： 視頻交叉點(diǎn)開關(guān)
電路： 1 x 16:5
電壓電源： 雙電源
電壓 - 電源，單路/雙路(±)： ±4.5 V ~ 5.5 V
電流 - 電源： 30mA
工作溫度： -40°C ~ 85°C
安裝類型： 表面貼裝
封裝/外殼： 80-LQFP
供應(yīng)商設(shè)備封裝： 80-LQFP（12x12）
包裝： 托盤
AD8106/AD8107
Rev. 0 | Page 19 of 28
Obviously, some subset of all these cases must be selected to be
used as a guide for a practical measure of crosstalk. One
common method is to measure all hostile crosstalk, which
means that the crosstalk to the selected channel is measured
while all other system channels are driven in parallel. In general,
this yields the worst crosstalk number, but this is not always the
case due to the vector nature of the crosstalk signal.
From a circuit standpoint, the input crosstalk mechanism looks
like a capacitor coupling to a resistive load. For low frequencies,
the magnitude of the crosstalk is given by
(
)
[
]s
C
R
XT
M
S
×
=
10
log
20
(2)
where:
RS is the source resistance.
C
Other useful crosstalk measurements are those created by one
of the nearest neighbors or by two of the nearest neighbors on
either side. These crosstalk measurements are generally higher
than those of more distant channels, so they can serve as a
worst-case measure for any other one-channel or two-channel
crosstalk measurements.
M
is the mutual capacitance between the test signal circuit and
the selected circuit.
s is the Laplace transform variable.
Equation 2 shows that this crosstalk mechanism has a high-pass
nature; it can also be minimized by reducing the coupling
capacitance of the input circuits and lowering the output
impedance of the drivers. If the input is driven from a 75 Ω
terminated cable, the input crosstalk can be reduced by
buffering this signal with a low output impedance buffer.
Input and Output Crosstalk
The flexible programming capability of the AD8106/AD8107
can be used to diagnose whether crosstalk is occurring more on
the input side or the output side. For example, a given input
channel, such as IN07 in the middle, can be programmed to
drive OUT01. The input to IN07 is terminated to ground (via
50 Ω or 75 Ω) and no signal is applied.
On the output side, the crosstalk can be reduced by driving a
lighter load. Although the AD8106/AD8107 are specified with
excellent differential gain and phase when driving a standard
150 Ω video load, the crosstalk is higher than the minimum
obtainable because of the high output currents. These currents
induce crosstalk via the mutual inductance of the output pins
and bond wires of the AD8106/AD8107.
All the other inputs are driven in parallel with the same test
signal (practically provided by a distribution amplifier) with all
other outputs disabled, except OUT01. Because grounded IN07
is programmed to drive OUT01, no signal should be present. If
any signal is present, it can be attributed to the other 15 hostile
input signals because no other outputs are driven; that is, they
are all disabled. Thus, this method measures the all-hostile input
contribution to crosstalk into IN07. This method can also be used
for other input channels and combinations of hostile inputs.
From a circuit standpoint, this output crosstalk mechanism
looks like a transformer with a mutual inductance between the
windings that drive a load resistor. For low frequencies, the
magnitude of the crosstalk is given by
(
)
L
R
s
Mxy
XT
/
log
20
10
×
=
(3)
For output crosstalk measurement, a single input channel
(IN00, for example) is driven and all outputs other than a given
output are programmed to connect to IN00. OUT01 is
programmed to connect to IN15, which is far away from IN00,
and is terminated to ground. As a result, OUT01 should not
have a signal present because it is listening for a quiet input.
Any signal measured at the OUT01 can be attributed to the
output crosstalk of the other seven hostile outputs. Again, this
method can be modified to measure other channels and other
crosspoint matrix combinations.
where:
Mxy is the mutual inductance of output x to output y.
R is the load resistance on the measured output.
L
This crosstalk mechanism can be minimized by keeping the
mutual inductance low and increasing RL. The mutual
inductance can be kept low by increasing the spacing of the
conductors and minimizing their parallel length.
PCB LAYOUT
Effect of Impedances on Crosstalk
Extreme care must be exercised to minimize additional
crosstalk generated by the system circuit board(s). The areas
that must be carefully detailed are grounding, shielding, signal
routing, and supply bypassing.
The input side crosstalk can be influenced by the output
impedance of the sources that drive the inputs. The lower the
impedance of the drive source, the lower the magnitude of the
crosstalk. The dominant crosstalk mechanism on the input side
is capacitive coupling. The high impedance inputs do not have
significant current flow to create magnetically induced crosstalk.
However, significant current can flow through the input
termination resistors and the loops that drive them. Thus,
the PC board on the input side can contribute to magnetically
coupled crosstalk.
The packaging of the AD8106/AD8107 is designed to help keep
the crosstalk to a minimum. Each input is separated from other
inputs by an analog ground pin. All of these AGNDs should be
connected directly to the ground plane of the circuit board.
These ground pins provide shielding, low impedance return
paths, and physical separation for the inputs. All of these help to
reduce crosstalk.
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