參數(shù)資料
型號： THS7364IPW
廠商： TEXAS INSTRUMENTS INC
元件分類： 音頻／視頻放大
英文描述： 6 CHANNEL, VIDEO AMPLIFIER, PDSO20
封裝： GREEN, PLASTIC, TSSOP-20
文件頁數(shù)： 25/47頁
文件大?。?/td> 1134K
代理商： THS7364IPW
Level
Shift
Internal
Circuitry
+3.3V
800kW
R
PU
Input
Pin
Input
C
0.1 F
m
IN
V
=V
DC
S
800kW
800k
+R
W
PU
www.ti.com
SBOS530 – AUGUST 2010
This discharge current must not be large enough to
properly set the dc operating point within the
alter the video signal appreciably or picture quality
THS7364. This function is easily accomplished with
issues may arise. This effect is often seen by looking
the THS7364 by simply adding an external pull-up
at the tilt (droop) of a constant luma signal being
resistor to the positive power supply, as shown in
applied and the resulting output level. The associated
change in luma level from the beginning and end of
the video line is the amount of line tilt (droop).
If the discharge current is very small, the amount of
tilt is very low, which is a generally a good thing.
However, the amount of time for the system to
capture the sync signal could be too long. This effect
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- and ac-coupling in the same
part, the THS7364 incorporates an 800-k
resistor to
Figure 80. AC-Bias Input Mode Circuit
ground. Although a true constant current sink is
Configuration
preferred over a resistor, there can be issues when
the voltage is near ground. This configuration can
cause the current sink transistor to saturate and
The dc voltage appearing at the input pin is equal to
cause potential problems with the signal. The 800-k
resistor is large enough 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,
(1)
then there is 1 V/800 k
= 1.25-mA of discharge
The THS7364 allowable input range is approximately
current. If more hum rejection is desired or there is a
0 V to (VS+ – 1.5 V), allowing for a very wide input
loss of sync occurring, then simply decrease the
voltage range. As such, the input dc bias point is very
0.1-mF input coupling capacitor. A decrease from
flexible, with the output dc bias point being the
0.1 mF to 0.047 mF increases the hum rejection by a
primary factor. For example, if the output dc bias
factor of 2.1. Alternatively, an external pull-down
point is desired to be 1.6 V on a 3.3-V supply, then
resistor to ground may be added that decreases the
the input dc bias point should be (1.6 V – 300 mV)/2
overall
resistance
and
ultimately
increases
the
= 0.65 V. Thus, the pull-up resistor calculates to
discharge current.
approximately 3.3 M
, resulting in 0.644 V. If the
To ensure proper stability of the ac STC control loop,
output dc-bias point is desired to be 1.6 V with a 5-V
the source impedance must be less than 1-k
with
power supply, then the pull-up resistor calculates to
the input capacitor in place. Otherwise, there is a
approximately 5.36 M
.
possibility of the control loop ringing, which may
Keep in mind that the internal 800-k
resistor has
appear on the output of the THS7364. Because most
approximately
a
±20%
variance.
As
such,
the
DACs or encoders use resistors to establish the
calculations should take this variance into account.
voltage, which are typically less than 300-
, meeting
For the 0.644-V example above, using an ideal
the less than 1-k
requirement is easily done.
3.3-M
resistor,
the
input
dc
bias
voltage
is
However, if the source impedance looking from the
approximately 0.644 V ± 0.1 V.
THS7364 input perspective is very high, then simply
adding a 1-k
resistor to GND ensures proper
The value of the output bias voltage is very flexible
operation of the THS7364.
and is left to each individual design. It is important to
ensure that the signal does not clip or saturate the
INPUT MODE OF OPERATION: AC BIAS
video signal. Thus, it is recommended to ensure the
output bias voltage is between 0.9 V and (VS+ – 1 V).
Sync-tip clamps work very well for signals that have
For 100% color saturated CVBS or signals with
horizontal and/or vertical syncs associated with them;
Macrovision, the CVBS signal can reach up to
however, some video signals do not have a sync
1.23 VPP at the input, or 2.46 VPP at the output of the
embedded within the signal. If ac-coupling of these
THS7364. In contrast, other signals are typically
signals is desired, then a dc bias is required to
1 VPP or 0.7 VPP at the input which translate to an
output voltage of 2 VPP or 1.4 VPP. The output bias
voltage must account for a worst-case situation,
depending on the signals involved.
Copyright 2010, Texas Instruments Incorporated
31
Product Folder Link(s): THS7364
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相關代理商/技術(shù)參數(shù)
參數(shù)描述
THS7364IPWR 功能描述:視頻放大器 6-Ch Video Amp RoHS:否 制造商:ON Semiconductor 通道數(shù)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
THS7365 制造商:TI 制造商全稱:Texas Instruments 功能描述:6-Channel Video Amplifier with 3-SD and 3-HD Sixth-Order Filters and 6-dB Gain
THS7365EVM 功能描述:放大器 IC 開發(fā)工具 THS7365EVM Eval Mod RoHS:否 制造商:International Rectifier 產(chǎn)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
THS7365IPW 功能描述:視頻放大器 6Ch Video Amp RoHS:否 制造商:ON Semiconductor 通道數(shù)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
THS7365IPWR 功能描述:視頻放大器 6Ch Video Amp RoHS:否 制造商:ON Semiconductor 通道數(shù)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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