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參數資料
| 型號： | THS7316DR |
| 廠商： | TEXAS INSTRUMENTS INC |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | 3 CHANNEL, VIDEO AMPLIFIER, PDSO8 |
| 封裝： | GREEN, PLASTIC, MS-012AA, SOIC-8 |
| 文件頁數： | 7/28頁 |
| 文件大小： | 988K |
| 代理商： | THS7316DR |
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INPUT MODE OF OPERATION – AC BIAS
SLOS521A – MARCH 2007 – REVISED JANUARY 2008
current. As previously described, if the input signal goes below the 0-V clamp level, the internal loop of the
THS7316 will source current to increase the voltage appearing at the input pin. As the difference between the
signal
level
and
the
0-V
reference
level
increases,
the
amount
of
source
current
increases
proportionally—supplying up to 3-mA of current. Thus the time to re-establish the proper STC voltage can be
fast. If the difference is small, then the source current is also small to account for minor voltage droop.
But, what happens if the input signal goes above the 0-V input level? The problem is the video signal is always
above this level, and must not be altered in any way. But if the Sync level of the input signal is above this 0-V
level, then the internal discharge (sink) current will discharge the ac-coupled bias signal to the proper 0-V level.
This discharge current must not be large enough to alter the video signal appreciably, or picture quality issues
may arise. This is often seen by looking at the tilt (aka droop) of a constant luma signal being applied and looking
at the resulting output level. The associated change in luma level from the beginning of the video line to the end
of the video line is the amount of line tilt (droop).
If the discharge current is small, the amount of tilt is low which is good. But, the amount of time for the system to
capture the sync signal could be too long. This is also termed hum rejection. Hum arises from the ac line voltage
frequency of 50-Hz or 60-Hz. The value of the discharge current and the ac-coupling capacitor combine to dictate
the hum rejection and the amount of line tilt.
To allow for both dc-coupling and ac-coupling in the same part, the THS7316 incorporates an 800-k
resistor to
ground. Although a true constant current sink is preferred over a resistor, there are significant issues when the
voltage is near ground. This can cause the current sink transistor to saturate and cause potential problems with
the signal. This resistor is large enough as to not impact a dc-coupled DAC termination. For discharging an
ac-coupled source, Ohm’s Law is used. If the video signal is 1 V, then there is 1 V / 800 k
= 1.25-
A of
discharge current. If more hum rejection is desired or there is a loss of sync occurring, then decrease the 0.1-
F
input coupling capacitor. A decrease from 0.1
F to 0.047 F increases the hum rejection by a factor of 2.1.
Alternatively an external pull-down resistor to ground may be added which decreases the overall resistance, and
ultimately increases the discharge current.
To ensure proper stability of the AC STC control loop, the source impedance must be less than 1-k
with the
input capacitor in place. Otherwise, there is a possibility of the control loop to ring and this ringing may appear on
the output of the THS7316. Because most DACs or encoders use resistors to establish the voltage, which are
typically less than 300-
, then meeting the <1-k requirement is done. But, if the source impedance looking from
the THS7316 input perspective is high, then add a 1-k
resistor to GND to ensure proper operation of the
THS7316.
Sync tip clamps work well for signals that have horizontal and/or vertical syncs associated with them. But, some
video signals do not have a sync embedded within the signal – such as Chroma or the P’B and P’R channels of a
480i/480p/576i/576p signal; or the bottom of the sync is not the lowest possible level of the video signal – such
as the P’B and P’R channels of a 720p and 1080i signal. If ac-coupling of these signals is desired, then a dc bias
is required to properly set the dc operating point within the THS7316. This function is easily accomplished with
the THS7316 by adding an external pull-up resistor to the positive power supply as shown in Figure 30.
Copyright 2007–2008, Texas Instruments Incorporated
15
Product Folder Link(s) :THS7316
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相關代理商/技術參數 |
參數描述 |
|---|---|
| THS7316DRG4 | 功能描述:視頻放大器 3-Ch HDTV Video Amp RoHS:否 制造商:ON Semiconductor 通道數量:4 電源類型: 工作電源電壓:3.3 V, 5 V 電源電流: 最小工作溫度: 最大工作溫度: 封裝 / 箱體:TSSOP-14 封裝:Reel |
| THS7316EVM | 功能描述:放大器 IC 開發工具 THS7316 Eval Mod RoHS:否 制造商:International Rectifier 產品:Demonstration Boards 類型:Power Amplifiers 工具用于評估:IR4302 工作電源電壓:13 V to 23 V |
| THS7318 | 制造商:TI 制造商全稱:Texas Instruments 功能描述:3-Channel Low-Power EDTV/SDTV Video Line Driver With Low-Pass Filters |
| THS7318_07 | 制造商:TI 制造商全稱:Texas Instruments 功能描述:3-Channel Low-Power EDTV/SDTV Video Line Driver With Low-Pass Filters |
| THS7318YZFR | 功能描述:視頻放大器 3-Ch L-P EDTV/SDTV Video Line Driver RoHS:否 制造商:ON Semiconductor 通道數量:4 電源類型: 工作電源電壓:3.3 V, 5 V 電源電流: 最小工作溫度: 最大工作溫度: 封裝 / 箱體:TSSOP-14 封裝:Reel |
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