EL4501IU Intersil, EL4501IU Datasheet - Page 15

• Manufacturer Part Number: EL4501IU
• Description: IC VIDEO FRONT END AMP 24-QSOP
• Manufacturer: Intersil

Specifications of EL4501IU

• Applications: Video Front End (VFE)
• Number Of Circuits: 1
• -3db Bandwidth: 100MHz
• Slew Rate: 96 V/µs
• Current - Supply: 10.5mA
• Current - Output / Channel: 70mA
• Voltage - Supply, Single/dual (±): 4.5 V ~ 5.5 V
• Mounting Type: Surface Mount
• Package / Case: 24-QSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Block Diagram
Applications Information
Product Description
The EL4501 is a video front-end sub-system comprised of a
video amplifier with DC-restore, an adjustable threshold data
slicer, and an advanced sync separator. The prime function
of the system is to DC-stabilize and buffer AC-coupled
analog video signals and to extract timing reference signals
embedded in the video signal. An adjustable threshold data
slicer incorporated into the EL4501 may be used to extract
data embedded within the active video or VBI regions of a
video signal.
Theory of Operation
DC-RESTORE LOOP
When video signals are distributed, it is common to employ
capacitive coupling to prevent DC current flow due to
differences in local grounds or signal reference levels.
However, the coupling capacitor causes the DC level of the
signal post capacitor to be dependent on the video
(luminance) content of the waveform. A DC-restore loop is
used to correct this behavior by moving a portion of the
video waveform to a DC reference level in response to a
control signal. When the loop is operating, DC drift
VIDEO
INPUT
0.1µF
0.1µF
SYNC AMP
VIDEO IN
SYNC IN
15
RFREQ
FSEL
LOS
V
S
FILTER
GND
V
SD
+
-
EL4501
SEPARATOR
SLICE
MODE
SYNC
accumulates over a single line only, before it is corrected.
The peak value of drift is limited by the rate of the control
signal (typically video line rate) and the AC coupling time
constant.
The restore loop is comprised of a 100MHz forward video
amplifier, combined with a nulling amplifier and sample and
hold circuit. For maximum flexibility the hold capacitor is
placed off-chip, allowing the loop response rate to be tailored
for specific applications and minimizing hold-step problems.
The loop provides a restore current peak of ±20µA at room
temperature. Figure 36 shows the amplifier and S/H
connection. During normal operation the internally generated
DC-restore control signal is timed to the back porch of the
video waveform. Figure 37 shows an NTSC video signal,
along with the EL4501 BACK PORCH output. In operation,
BACK PORCH activates the S/H switch, completing the
nulling feedback loop and driving the video amplifier output
towards the reference voltage. At the end of BACK PORCH,
the external capacitor holds the correction voltage for the
remainder of the video line. In the absence of a valid input
signal, the chip generates a repetitive, arbitrary restore
control signal at the line rate set by the external resistor
R
TRACK/
HOLD
FREQ
DS REF
GND
. Although uncorrelated to the input, the pulse
D
+
-
+
-
+
-
1.3V
DS MODE
DS OUT
DS ENABLE
VIDEO OUT
VFB
REF IN
REF OUT
BACK PORCH
COMPOSITE
HORIZONTAL
VERTICAL
ODD/EVEN
C
HOLD
C
REF
R
R
F
G