ADV3201ASWZ Analog Devices Inc, ADV3201ASWZ Datasheet - Page 33

• Manufacturer Part Number: ADV3201ASWZ
• Description: 132x32 Crosspoint W/Sync Tip Clamp & OSD
• Manufacturer: Analog Devices Inc

Specifications of ADV3201ASWZ

• Function: Crosspoint Switch
• Circuit: 1 x 32:32
• On-state Resistance: 150 Ohm
• Voltage Supply Source: Single, Dual Supply
• Voltage - Supply, Single/dual (±): 5V, ±2.5V, ±3.3V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 176-LQFP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Measuring Crosstalk
Crosstalk is measured by applying a signal to one or more
channels and measuring the relative strength of that signal on a
desired selected channel. The measurement is usually expressed
as decibels below the magnitude of the test signal. The crosstalk
is expressed by
where:
s = jω (Laplace transform variable).
A
selected channel.
A
It can be seen that crosstalk is a function of frequency but not a
function of the magnitude of the test signal (to first order). In
addition, the crosstalk signal has a phase relative to the test
signal associated with it.
A network analyzer is most commonly used to measure cross-
talk over a frequency range of interest. It can provide both
magnitude and phase information about the crosstalk signal.
As a crosspoint system or device grows larger, the number of
theoretical crosstalk combinations and permutations can become
extremely large. For example, in the case of the 32 × 32 matrix
of the ADV3200/ADV3201, note the number of crosstalk terms
that can be considered for a single channel, for example, the IN00
input. IN00 is programmed to connect to one of the ADV3200/
ADV3201 outputs where the measurement can be made.
First, the crosstalk terms associated with driving a test signal
into each of the other 31 inputs can be measured one at a time,
while applying no signal to IN00. Then the crosstalk terms
associated with driving a parallel test signal into all 31 other
inputs can be measured two at a time in all possible combina-
tions, then three at a time, and so on until, finally, there is only
one way to drive a test signal into all 31 other inputs in parallel.
Each of these cases is legitimately different from the others and
may yield a unique value, depending on the resolution of the
measurement system, but it is hardly practical to measure all
these terms and then specify them. In addition, this describes
the crosstalk matrix for just one input channel. A similar cross-
talk matrix can be proposed for every other input. In addition,
if the possible combinations and permutations for connecting
inputs to the other outputs (not used for measurement) are
taken into consideration, the numbers quickly grow to astro-
nomical proportions. If a larger crosspoint array of multiple
ADV3200/ADV3201 devices is constructed, the numbers grow
larger still.
Obviously, some subset of all these cases must be selected as a
guide for a practical measurement of crosstalk. One common
method is to measure all hostile crosstalk; this means that the
crosstalk to the selected channel is measured while all other
SEL
TEST
(s) is the amplitude of the crosstalk induced signal in the
(s) is the amplitude of the test signal.
XT
=
20
log
10
⎛
⎜
⎜
⎝
A
A
TEST
SEL
(
(
s
s
)
)
⎞
⎟
⎟
⎠
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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.
Other useful crosstalk measurements are those created by one
nearest neighbor or by the two nearest neighbors on either side.
These crosstalk measurements are generally higher than those
of more distant channels; therefore, they can serve as a worst-
case measure for any other one-channel or two-channel crosstalk
measurements.
Input and Output Crosstalk
Capacitive coupling is voltage-driven (dV/dt) but is generally a
constant ratio. Capacitive crosstalk is proportional to input or
output voltage, but this ratio is not reduced by simply reducing
signal swings. Attenuation factors must be changed by changing
impedances (lowering mutual capacitance), or destructive
canceling must be utilized by summing equal and out of phase
components. For high input impedance devices such as the
ADV3200/ADV3201, capacitances generally dominate input-
generated crosstalk.
Inductive coupling is proportional to current (dI/dt) and often
scales as a constant ratio with signal voltage, but it also shows a
dependence on impedances (load current). Inductive coupling
can also be reduced by constructive canceling of equal and out
of phase fields. In the case of driving low impedance video
loads, output inductances contribute highly to output crosstalk.
The flexible programming capability of the ADV3200/ADV3201
can be used to diagnose whether crosstalk is occurring more on
the input side or the output side. Some examples are illustrative.
A given input pair (IN07 in the middle for this example) can be
programmed to drive OUT07 (also in the middle). The inputs
to IN07 are terminated to ground (via 50 Ω or 75 Ω resistors)
and no signal is applied.
All the other inputs are driven in parallel with the same test signal
(practically provided by a distribution amplifier), with all other
outputs except OUT07 disabled. Because the grounded IN07
input is programmed to drive OUT07, no signal should be
present. Any signal that is present can be attributed to the other
15 hostile input signals because no other outputs are driven
(they are all disabled). Thus, this method measures all the
hostile input contribution to crosstalk into IN07. Of course, this
method can be used for other input channels and combinations
of hostile inputs.
For output crosstalk measurement, a single input channel is
driven (IN00, for example) and all outputs other than a given
output (IN07 in the middle) are programmed to connect to
IN00. OUT07 is programmed to connect to IN15 (far away
from IN00), which is terminated to ground. Thus OUT07
should not have a signal present because it is listening to a quiet
input. Any signal measured at OUT07 can be attributed to the
output crosstalk of the other 15 hostile outputs. Again, this
method can be modified to measure other channels and other
crosspoint matrix combinations.
ADV3200/ADV3201