FMS6408_07 Datasheet, PDF (7/11 Pages) Fairchild Semiconductor – Precision Triple Video Filter Driver for RGB and YUV Signals

Functional Description
Introduction
This product is a three-channel monolithic continuous
time video filter designed for reconstructing YUV, YC
CV, or RGB signals from a video D/A source. Inputs
should be AC coupled while outputs can be either AC or
DC coupled. The reconstruction filters approximate a
5^th-order Butterworth response, optimized for minimum
overshoot and flat group delay. This provides a
maximally flat response in terms of delay and
amplitude. Each of the three outputs is capable of
driving 2VPP into 75Ω loads.
All channels are clamped during the sync interval to set
the appropriate DC output level. Sync tip clamping
greatly reduces the effective input time constant,
allowing the use of small, low-cost input coupling
capacitors. The input settles to 10mV in 2ms for typical
DC shifts present in the video signal.
In most applications, the input coupling capacitors are
0.1µF. The inputs typically sink 1µA of current during
active video. For YUV signals, this translates into a 2mV
tilt in a horizontal line 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 affects the amount of tilt
per line. Any reduction in tilt comes with an increase in
settling time.
Inputs
The inputs are typically be driven by either a low-
impedance source of 1Vpp or the output of a 75Ω
terminated line driven by the output of a current DAC. In
either case, the inputs must be capacitively coupled to
allow the sync-detect and DC-restore circuitry to
operate properly.
Outputs
The outputs are low-impedance voltage drivers that can
handle either a single or dual load. A single load
consists of a 75Ω-series termination resistor feeding a
75Ω-terminated line for a total load at the part of 150Ω.
Even when two loads are present (75Ω) the driver
produces a full 2VPP signal at its output pin. The driver
can also be used to drive an AC coupled single or dual
load. When driving a dual load, either output functions if
the other output connection is inadvertently shorted,
providing these loads are AC coupled.
© 2004 Fairchild Semiconductor Corporation
FMS6408 Rev. 3.0.0
7
www.fairchildsemi.com