FMS6501 Datasheet, PDF (10/16 Pages) Fairchild Semiconductor – 12 Input 9 Output Video Switch Matrix with Input Clamp, Input Bias Circuitry, and Output Drivers

Each of the FMS6501 outputs can be independently powered
down and placed in a high impedance state with the ENABLE
bit. This function can be used to mute video signals, to parallel
multiple FMS6501 outputs, or to save power. When the output
amplifier is disabled, the high impedance output presents a 3kΩ
load to ground. The output amplifier will typically enter and
recover from the power down state in less than 300ns after
being programmed.
When an output channel is not connected to an input, the input
to that particular channels amplifier is forced to approximately
150mV. The output amplifier is still active, unless specifically
disabled by the I²C interface. Voltage output levels will depend
on the programmed gain for that channel.
Crosstalk
Crosstalk is an important consideration when using the
FMS6501. Input and output crosstalk are defined to represent
the two major coupling modes that may be present in a typical
application. Input crosstalk is crosstalk in the input pins and
switches when the interfering signal drives an open switch. It is
dominated by inductive coupling in the package lead frame
between adjacent leads. It decreases rapidly as the interfering
signal moves farther away from the pin adjacent to the input sig-
nal selected. Output crosstalk is coupling from one driven out-
put to another active output. It decreases with increasing load
impedance as it is caused mainly by ground and power coupling
between output amplifiers. So if a signal is driving an open
switch, its crosstalk will be mainly input crosstalk. If it is driving a
load through an active output, its crosstalk will be mainly output
crosstalk.
Input and output crosstalk measurements are performed with
the test configuration shown below:
TERMINATION
Bias
IN1
For input crosstalk, the switch is open. All inputs are in bias
mode. Channel 1 input is driven with a 1V_pp signal, while all
other inputs are AC terminated with 75 ohms. All outputs are
enabled, and crosstalk is measured from IN1 to any output.
For output crosstalk, the switch is closed. Crosstalk from OUT1
to any output is measured.
Crosstalk from multiple sources into a given channel was mea-
sured with the setup shown in figure 6. Here, Input In1 is driven
with a 1V_pp pulse source and is connected to outputs Out1 to
Out8. Input In9 is driven with a secondary, asynchronous gray
field video signal, and is connected to Out9. All other inputs are
AC terminated with 75 ohms. Crosstalk effects on the gray field
are then measured and calculated with respect to a standard
1V_pp output measured at the load.
If all inputs and outputs are not needed, avoid using adjacent
channels where possible to reduce crosstalk. Disable all unused
channels to further reduce crosstalk as well as power dissipa-
tion.
TERMINATION
IN1
Bias
IN1 driven with
SD video 1Vpp.
IN9 driven with
asynchronous
SD video 1Vpp.
IN2-8, 10-12 are
AC-term to GND
w/75 ohms.
IN9
Bias
IN12
Bias
IN2 - IN12 are
AC-Term to
Ground
w/75 ohms
IN1 = 1Vpp
Open switch
for input
crosstalk.
Close switch
for output
crosstalk.
OUT1
Measure Crosstalk from
channels 1-8 into
channel 9
OUT9
Figure 6: Test Configuration for Multi-Channel Crosstalk
IN12
Bias
Gain = 6dB
Out1 = 2.0Vpp
OUT1
Input Crosstalk from IN1
to OUTx
Output Crosstalk from
OUT1 to OUTx
OUT9
Figure 5: Test Configuration for Crosstalk
FMS6501 Rev. 1A
10
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