Data Sheet

© 2012 Fairchild Semiconductor Corporation www.fairchildsemi.com
FMS6501A • Rev. 1.0.0 10
FMS6501A — 12x9 Video Switch Matrix with Input Clamp, Input Bias Circuitry, and Output Drivers
Thermal issues are reduced with AC-coupled outputs,
eliminating special PC layout requirements.
Each of the 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 FMS6501A outputs, or to
save power. When the output amplifier is disabled, the
high-impedance output presents a 3 k load to ground.
The output amplifier typically enters and recovers from
the power-down state in less than 300 ns after being
programmed.
When an output channel is not connected to an input,
the input to that channel’s amplifier is forced to ~150mV.
The output amplifier is active unless specifically
disabled by the I
2
C interface. Voltage output levels
depend on the programmed gain for the channel.
Crosstalk
Crosstalk is an important consideration: input and output
crosstalk represent the two major coupling modes 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
signal selected. Output crosstalk is coupling from one
driven output to another active output. It decreases with
increasing load impedance, as it is caused mainly by
ground and power coupling between output amplifiers. If
a signal is driving an open switch, its crosstalk is mainly
input crosstalk. If it is driving a load through an active
output, its crosstalk is mainly output crosstalk.
Input and output crosstalk measurements are performed
with the test configuration shown in Figure 12.
Figure 12. Test Configuration for Crosstalk
For input crosstalk, the switch is open. All inputs are in
bias mode. Channel 1 input is driven with a 1 V
PP
signal,
while all other inputs are AC terminated with 75 . 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
has been measured with the setup shown in Figure 13.
Input IN1 is driven with a 1 V
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 . Crosstalk effects on the gray field
are measured and calculated with respect to a standard
1 V
PP
output measured at the load.
If not all inputs and outputs are needed, avoid using
adjacent channels, where possible, to reduce crosstalk.
Disable all unused channels to further reduce crosstalk
and power dissipation.
Figure 13. Test Configuration for Multi-Channel
Crosstalk