FMS6406_06 Datasheet, PDF (10/12 Pages) Fairchild Semiconductor – Precision S-Video Filter with Summed Composite Output, Sound Trap, and Group Delay Compensation

Functional Description
Introduction
This product is a two channel monolithic continuous time
video filter designed for reconstructing the luminance and
chrominance signals from an S-Video D/A source.
Composite video output is generated by summing the Y
and C outputs. The chip is designed to have AC coupled
inputs and will work equally well with either AC or DC
coupled outputs.
The reconstruction filters provide a 5th-order Butterworth
response with group delay equalization. This provides a
maximally flat response in terms of delay and amplitude.
Each of the four outputs is capable of driving 2V_pp into a
75Ω load.
All channels are clamped during the sync interval to set the
appropriate minimum output DC level. With this operation
the effective input time constant is greatly reduced, which
allows for the use of small low cost coupling capacitors.
The net effect is that the input will settle to 10mV in 5ms
for any DC shifts present in the input video signal.
In most applications the input coupling capacitors are
0.1μF. The Y and C inputs typically sink 1μA of current
during active video, which normally tilts a horizontal line
by 2mV at the Y output. During sync, the clamp restores
this leakage current by sourcing an average of 20μA over
the clamp interval. Any change in the coupling capacitor
values will affect the amount of tilt per line. Any reduction
in tilt will come with an increase in settling time.
Luminance (Y) I/O
The typical luma input is driven by either a low impedance
source of 1V_pp or the output of a 75Ω terminated line
driven by the output of a current DAC. In either case, the
input must be capacitively coupled to allow the sync-
detect and DC restore circuitry to operate properly.
All outputs are capable of driving 2V_pp, AC or DC-coupled,
into either a single or dual video load. A single video load
consists of a series 75Ω impedance matching resistor
connected to a terminated 75Ω line, this presents a total
of 150Ω of loading to the part. A dual load would be two of
these in parallel which would present a total of 75Ω to the
part. The gain of the Y, C and CV signals is 6dB with 1V_pp
input levels. Even when two loads are present the driver
will produce a full 2V_pp signal at its output pin.
Chrominance (C) I/O
The chrominance input can be driven in the same manner
as the luminance input but is typically only a 0.7V_pp signal.
Since the chrominance signal doesn’t contain any DC
content, the output signal can be AC coupled using as
small as a 0.1μF capacitor if DC-coupling is not desired.
Composite Video (CV) Output
The composite video output driver is same as the other
outputs. When driving a dual load either output will still
function if the other output connection is inadvertently
shorted providing these loads are AC-coupled.
Equalizer/Notch (EQ_NOTCH) Output
This output is designed to drive a 600Ω load to 2V_pp,
which will meet its primary intention of driving a modulator
load.
Layout Considerations
General layout and supply bypassing play major roles in
high-frequency performance and thermal characteristics.
The FMS6406DEMO is a 4-layer board with a full power
and ground plane. Following this layout configuration will
provide the optimum performance and thermal characte-
ristics. For optimum results, follow the steps below as a
basis for high frequency layout:
■ Include 1µF and 0.1µF ceramic bypass capacitors
■ Place the 1µF capacitor within 0.75 inches of the
power pin
■ Place the 0.1µF capacitor within 0.1 inches of the
power pin
■ For multi-layer boards, use a large ground plane to
help dissipate heat
■ For 2-layer boards, use a ground plane that extends
beyond the device by at least 0.5”
■ Minimize all trace lengths to reduce series inductances
© 2006 Fairchild Semiconductor Corporation
10
FMS6406 Rev. 4.0.4
www.fairchildsemi.com