MAX7450/MAX7451/MAX7452
Video-Signal Conditioners with AGC
and Back-Porch Clamp
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Automatic Gain Control (AGC)
The MAX7450/MAX7451/MAX7452 have an integrated
automatic gain-control circuit to ensure the sync ampli-
tude is normalized to the standard level, thus normalizing
the overall amplitude to a standard level. The accuracy
of the normalized amplitude assumes the ratio of active
video to sync amplitude is correct in the input video sig-
nal. The gain is adjusted automatically by detecting and
comparing the amplitude of the sync pulse to a fixed
internal reference. If the sync amplitude is less than this
value, the overall gain is increased until the sync ampli-
tude equals this reference. However, if the sync ampli-
tude is high, the overall gain is reduced accordingly.
Disable the AGC loop by driving AGCD high.
When designing the overall system, it is important to note
that the AGC can correct for termination problems. First,
disable the AGC and verify that the terminations are cor-
rect, and then enable the AGC for proper operation.
Output Buffer
The output buffer of the MAX7450/MAX7451/MAX7452
is designed to drive either standard video loads or
high-impedance loads, independent of the buffer gain.
Logic levels on GSET and AGCD set the gain of the
MAX7450/MAX7451/MAX7452. Table 1 shows the dif-
ferent gain-setting configurations.
Noise Filter
The MAX7450/MAX7451/MAX7452 feature a simple 2nd-
order lowpass filter to reject out-of-band noise that may
be introduced by the long cable connection between the
cameras and the switching matrix.
LOS Detector
The LOS detector of the MAX7450/MAX7451/MAX7452
outputs a logic high when the sync is not present (loss
of video signal) for at least 15 horizontal lines on the
input. This can be used to indicate a fault condition of
the camera or cable.
Applications Information
Connecting the MAX7450/MAX7451 to a
Crosspoint Switch
The MAX7450/MAX7451/MAX7452 are designed to
directly interface to a video crosspoint switching device
such as those used in security systems (see Figure 2).
The MAX7450/MAX7451 clamp the video output to
GND, making the devices an ideal interface to the
MAX4358 crosspoint switches and the MAX4455 OSD.
The MAX7450/MAX7451 and the MAX4455 have their
outputs referenced to ground, ensuring the amplitudes
and the brightness of the OSD relative to the video
signal are accurate.
Interfacing the MAX7452 to an ADC
The MAX7452 can be directly connected to an ADC or
video decoder as shown in Figure 3. The video output
of the MAX7452 is DC-coupled to a single-ended video
input on the ADC. The voltage on the BPLVL pin sets
the black level of the video signal at the output of the
MAX7452. Use a stable voltage reference for the
BPLVL voltage, ideally the same reference that is used
