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參數(shù)資料
| 型號(hào)： | CH7002D-V |
| 廠商： | Electronic Theatre Controls, Inc. |
| 英文描述： | Scalable VGA to NTSC/PAL Encoder |
| 中文描述： | 可擴(kuò)展顯卡至NTSC / PAL編碼器 |
| 文件頁數(shù)： | 8/36頁 |
| 文件大?。?/td> | 199K |
| 代理商： | CH7002D-V |
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CHRONTEL
CH7002D
8 201-0000-029 Rev6.1, 8/2/99
Color Burst Generation*
The CH7002 employs a proprietary technique for generating the color sub-carrier frequency. This method allows
the sub-carrier frequency to be accurately generated from a 14.31818 MHz crystal oscillator, leaving the accuracy of
the sub-carrier frequency independent of the sampling rate. As a result, the CH7002 is compatible with any VGA
chip, since the CH7002 sub-carrier frequency is not dependent on the pixel rates of VGA manufacturers. This
feature is a significant benefit, since even a ± 0.01% sub-carrier frequency variation may be enough to cause some
television monitors to lose color lock.
Internal Voltage Reference
The on-chip generated ADC voltage references are brought out to pins VREF1 and VREF2 for decoupling purposes.
VREF1 and VREF2 should each have a 0.1
μ
F decoupling capacitor between each pin and ground. VREF2 provides
a typical 2.5V reference used for setting the internal bias to the ADCs. VREF1 provides a typical 1.235V reference
used for setting the RGB input full scale at 0.75V. VREF1 can be forced by an external voltage reference to
accommodate different RGB input ranges. An additional on-chip bandgap circuit is used, in the DAC, to generate a
reference voltage, which in conjunction with a reference resistor at pin RSET, sets the output ranges of the DACs.
For each DAC, the current output per LSB step is determined by the following equation:
ILSB = V(RSET)/RSET * 1/24 = 1.235/324 * 1/24 = 159 uA (nominal)
The value of RSET can be adjusted to achieve a desired output signal level. A valid range for RSET is any value at
or over 300 ohms.
Operating Modes
The CH7002 is designed to accept certain limited input resolutions, primarily 640x480 and 800x600, from a VGA
type graphics controller. The CH7002 is also designed to support both NTSC and PAL output formats, with scaling
to provide either an overscanned or underscanned image, when displayed on a TV. This combination of input
resolution and output formatting results in a matrix of operating modes which are listed below, and are described in
detail in Table 2. Note that all of these modes may be set either by I
2
C programming or by direct pin programming:
Modes 2 and 3 support 640x480 into a NTSC format in overscan and underscan forms respectively.
Modes 1 and 4 support 640x480 into a PAL format in underscan and overscan forms respectively. Note that
Mode 1 is the recommended operating mode for this resolution because it provides a higher overall quality
image.
Modes 0 and 5 support 800x600 into a PAL format in underscan and overscan forms respectively.
Mode 6 supports 800x600 into a NTSC format in an underscan form.
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