MAX7469UTP-T Maxim Integrated, MAX7469UTP-T Datasheet - Page 8

• Manufacturer Part Number: MAX7469UTP-T
• Description: Video ICs
• Manufacturer: Maxim Integrated

Use the high level for bipolar signals, such as C (chro-
ma) or P
The MAX7469/MAX7470 accept component or com-
posite inputs. When configured for composite video
inputs, the color-burst filter is enabled; if configured for
component video inputs, the color-burst filter is dis-
abled. This filter is separate from the main filter and not
in the direct signal path so that it has no effect on the
overall frequency response. With normal video signals
and levels, the use of this color-burst filter has a negligi-
ble effect on the sync detection. It has a more signifi-
cant effect under conditions of low-signal amplitude
coupled with higher relative amplitude color burst.
When filtering a video signal without embedded sync
information, such as computer formats (RGBHV) with
separate sync signals, use the external sync mode (see
Table 3) and apply the horizontal sync source to the
EXTSYNC pin. The sync detector determines when the
clamp circuit is turned on.
The MAX7469/MAX7470 are able to detect positive or
negative polarity external syncs with TTL logic levels.
Use the I
external sync signal.
The internal video filter delivers an optimized response
with a steep transition band to achieve a wide pass-
band along with excellent stopband rejection. In addi-
tion, the filter is optimized to provide an excellent time
domain response with low overshoot.
Use the I
(-3dB cutoff frequency) of the filter in the MAX7469/
MAX7470 from less than the SD passband to beyond the
HD passband in 256 linear steps. Write command byte
12h to access the frequency register, followed by an 8-bit
HDTV Continuously Variable
Anti-Aliasing Filters
Table 1. Clamp Levels
8
Y P
INPUT SIGNAL
________________________________________________________________________________________
all signals)
CVBS Y C
R G B H V
b
FORMAT
Y P
P
G
r
S
(sync on
b
b
BR
/P
2
P
2
C interface to vary the frequency response
C interface to program the polarity of the
r
r
. See Table 1 for more details.
External Sync Detection (EXTSYNC)
CHANNEL 1 CHANNEL 2 CHANNEL 3
Component/Composite Selection
High
Low
Low
Low
Low
Setting the Filter Frequency
CLAMP LEVEL
High
High
High
Low
Low
High
High
High
High
Low
Filter
data word that corresponds to the desired frequency. See
the Frequency Register section for more details.
The frequency set by the MAX7469/MAX7470 is the
-3dB point. Set the frequency according to the desired
flat passband response.
Select the frequency response according to the resolution
of the video-signal format. High-definition signals require
higher bandwidth, while standard-definition signals
require less bandwidth. The actual bandwidth contained
in the video signal is a function of the visual resolution of
the signal. This bandwidth is typically less than what is
indicated by the format resolution (1080i, 720p, etc.). For
more information, see Maxim Application Note 750:
Bandwidth Versus Video Resolution , which is available on
www.maxim-ic.com.
The frequency response can be optimized to improve
the overall performance. It is important, at a minimum, to
meet the Nyquist criterion. Beyond this, the frequency
response can be further optimized. In oversampled sys-
tems, the sample rate is significantly more than the
desired passband response. The extra frequency span
between the passband and the sample rate contains
noise and other undesirable interferers that can be elimi-
nated by setting the corner frequency of the filter to just
pass the desired bandwidth. This results in a higher sig-
nal-to-noise ratio of the overall system.
The MAX7469/MAX7470 offer selectable filter bypass-
ing that allows the input video signals to bypass the
internal filters and reach the output buffers unfiltered.
Write the appropriate command byte to enable (0Eh) or
disable (0Fh) filter-bypass mode as shown Table 3.
Each output buffer can drive a 2V
video load. The MAX7469/MAX7470 can drive a DC- or
AC-coupled load. Output AC-coupling capacitors can
be eliminated when driving a cable, thereby eliminating
the normal adverse effects caused by these large
capacitors, such as line, and field-time distortion, also
known as droop. The output DC level is controlled to
limit the DC voltage on the cable so that the blanking
level of the video signal is always less than 1V, meeting
digital TV specification. See the Output Considerations
section for more information.
The MAX7469 features an overall gain of 0dB, while the
MAX7470 features an overall gain of +6dB. Use the
MAX7470 when driving a back-matched cable and the
Optimizing the Frequency Response
P-P
signal into a 150Ω
Output Buffer
Filter Bypass
Gain Options