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参数资料
| 型号： | AD723ARUZ |
| 厂商： | Analog Devices Inc |
| 文件页数： | 8/20页 |
| 文件大小： | 0K |
| 描述： | IC ENCODER RGB-NTSC/PAL 28-TSSOP |
| 标准包装： | 50 |
| 类型： | 视频编码器 |
| 应用： | 照相机，互联网设备，机顶盒 |
| 电压 - 电源，数字： | 2.7 V ~ 5.5 V |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 28-TSSOP（0.173"，4.40mm 宽） |
| 供应商设备封装： | 28-TSSOP |
| 包装： | 管件 |
| 产品目录页面： | 788 (CN2011-ZH PDF) |
REV. 0
AD723
–16–
One well-known distortion of composite video images is called
dot crawl. It shows up as a moving dot pattern at the interface
between two areas of different color. It is caused by the inability
of the monitor circuitry to adequately separate the luminance
and chrominance signals.
One way to prevent dot crawl is to use a video signal that has
separate luminance and chrominance. Such a signal is referred
to as S-video or Y/C-video. Since the luminance and chromi-
nance are already separated, the monitor does not have to perform
this function. The S-video outputs of the AD723 can be used to
create higher quality pictures when an S-video input is available
on the monitor.
Flicker
In a VGA conversion application, where the software-controlled
registers are correctly set, two techniques are commonly used
by VGA controller manufacturers to generate the interlaced
signal. Each of these techniques introduces a unique charac-
teristic into the display created by the AD723.
The artifacts described below are not due to the encoder or its
encoding algorithm as all encoders will generate the same dis-
play when presented with these inputs. They are due to the
method used by the controller display chip to convert a nonin-
terlaced output to an interlaced signal.
The first interlacing technique outputs a true interlaced signal
with odd and even fields (one each to a frame, Figure 10a). This
provides the best picture quality when displaying photography,
CD video, and animation (games, etc.). However, it will intro-
duce a defect commonly referred to as flicker into the display.
Flicker is a fundamental defect of all interlaced displays and is
caused by the alternating field characteristic of the interlace
technique. Consider a one pixel high black line that extends
horizontally across a white screen. This line will exist in only
one field and will be refreshed at a rate of 30 Hz (25 Hz for
PAL). During the time that the other field is being displayed the
line will not be displayed. The human eye is capable of detect-
ing this, and the display will be perceived to have a pulsating or
flickering black line. This effect is highly content-sensitive and is
most pronounced in applications where text and thin horizontal
lines are present. In applications such as CD video, photography,
and animation, portions of objects naturally occur in both odd
and even fields and the effect of flicker is imperceptible.
The second commonly-used technique is to output an odd and
even field that are identical (Figure 10b). This ignores the data
that naturally occurs in one of the fields. In this case the same
one-pixel-high line mentioned above would either appear as a
two-pixel-high line, (one pixel high in both the odd and even
field) or not appear at all if it is in the data that is ignored by the
controller. Which of these cases occurs is dependent on the
placement of the line on the screen. This technique provides a
stable (i.e., nonflickering) display for all applications, but small
text can be difficult to read and lines in drawings (or spread-
sheets) can disappear. As above, graphics and animation are not
particularly affected although some resolution is lost.
There are methods to dramatically reduce the effect of flicker
and maintain high resolution. The most common is to ensure
that display data never exists solely in a single line. This can be
accomplished by averaging/weighting the contents of successive/
multiple noninterlaced lines prior to creating a true interlaced
output (Figure 10c). In a sense, this provides an output that will
lie between the two extremes described above. The weight or
percentage of one line that appears in another, and the number
of lines used, are variables that must be considered in developing a
system of this type. If this type of signal processing is performed,
it must be completed prior to the data being presented to the
AD723 for encoding.
1
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44
5
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=+
NONINTERLACED
ODD FIELD
EVEN FIELD
a. Conversion of Noninterlace to Interlace
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1
3
4
5
6
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=
+
NONINTERLACED
ODD FIELD
EVEN FIELD
1
2
3
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7
b. Line-Doubled Conversion Technique
2
1
3
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5
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7
=+
NONINTERLACED
ODD FIELD
EVEN FIELD
1
2
3
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c. Line Averaging Technique
Figure 10.
Vertical Scaling
In addition to converting the computer-generated image from
noninterlaced to interlaced format, it is also necessary to scale
the image down to fit into NTSC or PAL format. The most
common vertical lines/screen for VGA display are 480 and 600
lines. NTSC can only accommodate approximately 400 visible
lines/frame (200 per field), PAL can accommodate 576 lines/
frame (288 per field). If scaling is not performed, portions of the
original image will not appear in the television display.
This line reduction can be performed by merely eliminating
every Nth (6th line in converting 480 lines to NSTC or every
25th line in converting 600 lines to PAL). This risks generation
of jagged edges and jerky movement. It is best to combine the
scaling with the interpolation/averaging technique discussed
above to ensure that valuable data is not arbitrarily discarded in
the scaling process. Like the flicker reduction technique men-
tioned above, the line reduction must be accomplished prior to
the AD723 encoding operation.
There is a new generation of VGA controllers on the market
specifically designed to utilize these techniques to provide a
crisp and stable display for both text- and graphics-oriented
applications. In addition, these chips rescale the output from the
computer to fit correctly on the screen of a television. A list of
known devices is available through Analog Devices’ Applications
group, but the most complete and current information will be
available from the manufacturers of graphics controller ICs.
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相关代理商/技术参数 |
参数描述 |
|---|---|
| AD723ARUZ-REEL | 功能描述:IC ENCODER RGB-NTSC/PAL 28-TSSOP RoHS:是 类别:集成电路 (IC) >> 接口 - 编码器，解码器，转换器 系列:- 产品变化通告:Development Systems Discontinuation 26/Apr/2011 标准包装:1 系列:- 类型:编码器 应用:DVB-S.2 系统 电压 - 电源，模拟:- 电压 - 电源，数字:- 安装类型:- 封装/外壳:模块 供应商设备封装:模块 包装:散装 其它名称:Q4645799 |
| AD723ARUZ-REEL7 | 功能描述:IC ENCODER RGB-NTSC/PAL 28-TSSOP RoHS:是 类别:集成电路 (IC) >> 接口 - 编码器，解码器，转换器 系列:- 产品变化通告:Development Systems Discontinuation 26/Apr/2011 标准包装:1 系列:- 类型:编码器 应用:DVB-S.2 系统 电压 - 电源，模拟:- 电压 - 电源，数字:- 安装类型:- 封装/外壳:模块 供应商设备封装:模块 包装:散装 其它名称:Q4645799 |
| AD723-EVAL | 制造商:Analog Devices 功能描述:AD723 EVALUATION BOARD - Bulk |
| AD723WARUZ-RL7 | 功能描述:RGB to NTSC/PAL Encoder IC Video 28-TSSOP 制造商:analog devices inc. 系列:- 包装:剪切带（CT） 零件状态:有效 类型:RGB 转 NTSC/PAL 编码器 应用:视频 电压 - 电源，模拟:2.7 V ~ 5.5 V 电压 - 电源，数字:2.7 V ~ 5.5 V 安装类型:表面贴装 封装/外壳:28-TSSOP（0.173"，4.40mm 宽） 供应商器件封装:28-TSSOP 标准包装:1 |
| AD724 | 制造商:AD 制造商全称:Analog Devices 功能描述:RGB to NTSC/PAL Encoder |
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