EL4393C
Triple 80 MHz Video Amplifier w Disable
Typical Application for EL4393
and General Rules for PCB
Layout
The figure shows two EL4393’s configured as a
2 1 RGB multiplexer and cable driver driving
75X back terminated cables Each channel of the
EL4393 is configured to give a gain of two to
make up for the losses of the back terminating
resistor
In this example the Disable pins of each RGB
section are driven by a complementary TTL ‘‘se-
lect’’ signal Larger multiplexers can be assem-
bled with a 1-of-n TTL decoder selecting each
RGB triplet
The circuit gives channel isolations of typically
better than
b
50 dB at 10 MHz and with a 20
dB decade slope extending down to better than
b
90 dB at frequencies below 100 kHz
The schematic does not show things like power
supply decoupling or pcb layout grounding and
signal returns but these will all affect the overall
performance of the circuit and care should be
taken with these aspects
It is recommended that the V
CC
and V
EE
pins
each be decoupled by a 0 1
mF
NPO or X7R di-
electric ceramic capacitors to ground within 0 1
inch of the part and in parallel with the 0 1
mF
A 47
mF
tantalum capacitor also to ground The
47
mF
capacitors should be within 0 25 inch of
their power pins The ground plane should be un-
derneath the package but cut away from the
In
b
inputs Care should be taken with the center
channel feedback it must be kept away from
any of the in
a
or in
b
pins if it has to go under
the package Route the G-out line between the
pin 3 ground and the pin 4 In
b
if going under
the package is essential Otherwise loop the G-
out trace around all the other circuitry to its Rf
resistor The Rf and if used Rg resistors should
be on the input side of the package to minimize
trace length on the In
b
pins
The digital input disables are on the output side
of the package so that a good ground plane down
the center of the board underneath the package
will isolate any fast edges from the sensitive in-
puts
7
ELANTEC [ ELANTEC SEMICONDUCTOR ]
