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参数资料
| 型号： | THS7303PW |
| 厂商： | TEXAS INSTRUMENTS INC |
| 元件分类： | 音频／视频放大 |
| 英文描述： | 3 CHANNEL, VIDEO AMPLIFIER, PDSO20 |
| 封装： | GREEN, PLASTIC, TSSOP-20 |
| 文件页数： | 25/60页 |
| 文件大小： | 1980K |
| 代理商： | THS7303PW |
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Signal
Internal
Circuitry
Video
Out
SAG
675 W
1kW
878 W
150 W
75 W
47 F
m
33 F
m
1
)
(675
) 878)
1k
+ 2.55 V V () 8.1 dB).
1
)
(675
150) ) 878
1k
+ 1 )
1k
1k +
2 V V (
) 6.0 dB)
SLOS479B
– OCTOBER 2005 – REVISED MARCH 2011
Although it is common to use the same capacitor values for all the video lines, the frequency bandwidth of the
chroma signal in a S-Video system are not required to go as low or as high as the frequency of the luma
channel. Thus, the capacitor values of the chroma line(s) can be smaller, such as 0.1
μF.
OUTPUT MODES OF OPERATION: AC-COUPLED WITH SAG CORRECTION
Other than the line droop issue, ac coupling has two other potential issues: size and cost. A 330-
μF to 1000-μF
capacitor is large and can be quite costly in a system. Multiply these items by the number of channels, and the
size and cost can be significant. However, it is still desirable to use ac coupling to insure interoperability among
video devices.
The SAG nomenclature represents signal amplitude gain correction in this document. SAG correction is a
method that is used to ac-couple the video signal while using much smaller value capacitors. SAG correction is
accomplished by manipulating the feedback network of the output buffer. The THS7303 was designed to take
advantage of this compensation scheme, while minimizing the number of external components required.
Figure 66 shows the basic configuration of the output buffer stage along with the SAG configuration driving a
single video line.
Figure 66. THS7303 Output Buffer Using SAG Corrected AC-Coupling
SAG compensation can be analyzed by looking at low frequency operation and high frequency operation. At low
frequencies, the impedance of the capacitors are high and the corresponding gain of the amplifier is:
(1)
At high frequencies, the impedance of the capacitors are low and the resulting gain of the amplifier is:
(2)
which is needed to counteract the doubly-terminated 75-
output divider (–6 dB) circuit, resulting in the video-out
signal equaling the input signal amplitude.
When the SAG output pin is connected directly to the amplifier output, as found in the dc-coupled and the
ac-coupled configurations, the gain is configured properly at 2 V/V (6 dB). The SAG pin is part of the negative
feedback network. Thus, the capacitors and traces should be constructed as close as possible to the THS7303 to
minimize parasitic issues. Failure to do so may result in ringing of the video signal.
If these large capacitors must be placed further than 15 mm away from the THS7303, it is recommended that a
0.01-
μF capacitor be placed between the output of the channel and the SAG pin. This capacitor should be placed
as close as possible to the THS7303 to minimize stray capacitance and inductance issues. Since SAG correction
targets the low frequency operation area, there is no drawback of adding this high frequency capacitor to the
circuit.
When SAG correction is used, the low-frequency gain is higher than the high-frequency gain (8.1 dB versus 6
dB). This gain counter acts the attenuation of the signal because of the increase in the 47-
μF capacitor
impedance. This amplifier gain increase is determined by the 33-
μF capacitor (and associated internal resistor
values) and causes a Q enhancement to occur at low frequencies (typically at about 15 Hz). The ratio of these
capacitor values determines the frequency and amplitude of this enhancement.
Copyright
2005–2011, Texas Instruments Incorporated
31
Product Folder Link(s): THS7303
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相关代理商/技术参数 |
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| THS7303PWG4 | 功能描述:视频放大器 3-Ch Low Power Video RoHS:否 制造商:ON Semiconductor 通道数量:4 电源类型: 工作电源电压:3.3 V, 5 V 电源电流: 最小工作温度: 最大工作温度: 封装 / 箱体:TSSOP-14 封装:Reel |
| THS7303PWR | 功能描述:视频放大器 3-Ch Low Power Video RoHS:否 制造商:ON Semiconductor 通道数量:4 电源类型: 工作电源电压:3.3 V, 5 V 电源电流: 最小工作温度: 最大工作温度: 封装 / 箱体:TSSOP-14 封装:Reel |
| THS7303PWRG4 | 功能描述:视频放大器 3-Ch Low Power Video RoHS:否 制造商:ON Semiconductor 通道数量:4 电源类型: 工作电源电压:3.3 V, 5 V 电源电流: 最小工作温度: 最大工作温度: 封装 / 箱体:TSSOP-14 封装:Reel |
| THS730A A2 | 制造商:Tektronix Inc 功能描述:OSCILLOSCOPE DSO/DMM 200MHZ |
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