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参数资料
| 型号： | THS7365IPW |
| 厂商： | TEXAS INSTRUMENTS INC |
| 元件分类： | 音频／视频放大 |
| 英文描述： | 6 CHANNEL, VIDEO AMPLIFIER, PDSO20 |
| 封装： | PLASTIC, TSSOP-20 |
| 文件页数： | 28/52页 |
| 文件大小： | 1599K |
| 代理商： | THS7365IPW |
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INPUT MODE OF OPERATION: DC
Level
Shift
Internal
Circuitry
+V
S
800kW
Input
Pin
SBOS467 – MARCH 2009.................................................................................................................................................................................................. www.ti.com
R’G’B’ (commonly mislabeled RGB) is also called
Other AGC circuits use the chroma burst amplitude
G’B’R’ (again commonly mislabeled as GBR) in
for amplitude control; reduction in the sync signals
professional video systems. The Society of Motion
does not alter the proper gain setting. However, it is
Picture
and
Television
Engineers
(SMPTE)
good engineering design practice to ensure that
component
standard
stipulates
that
the
luma
saturation/clipping does not take place. Transistors
information is placed on the first channel, the blue
always take a finite amount of time to come out of
color difference is placed on the second channel, and
saturation. This saturation could possibly result in
the red color difference signal is placed on the third
timing delays or other aberrations on the signals.
channel. This practice is consistent with the Y'/P'B/P'R
To eliminate saturation or clipping problems, the
nomenclature. Because the luma channel (Y') carries
THS7365 has a 150-mV input level shift feature. This
the sync information and the green channel (G') also
feature takes the input voltage and adds an internal
carries the sync information, it makes logical sense
+150-mV shift to the signal. Because the THS7365
that G' be placed first in the system. Because the
also has a gain of 6 dB (2 V/V), the resulting output
blue color difference channel (P'B) is next and the red
with a 0-V applied input signal is approximately 300
color difference channel (P'R) is last, then it also
mV. The THS7365 rail-to-rail output stage can create
makes logical sense to place the B' signal on the
this output level while connected to a typical video
second channel and the R' signal on the third
load. This configuration ensures that no saturation or
channel, respectfully. Thus, hardware compatibility is
clipping of the sync signals occur. This shift is
better achieved when using G'B'R' rather than R'G'B'.
constant, regardless of the input signal. For example,
Note that for many G'B'R' systems, sync is embedded
if a 1-V input is applied, the output is 2.3 V.
on all three channels, but this configuration may not
always be the case in all systems.
Because the internal gain is fixed at +6 dB, the gain
dictates what the allowable linear input voltage range
can be without clipping concerns. For example, if the
power supply is set to 3 V, the maximum output is
The inputs to the THS7365 allow for both ac- and
approximately 2.9 V while driving a significant amount
dc-coupled inputs. Many DACs or video encoders can
of current. Thus, to avoid clipping, the allowable input
be dc-connected to the THS7365. One of the
is ([2.9 V/2] – 0.15 V) = 1.3 V. This range is valid for
drawbacks to dc-coupling is when 0 V is applied to
up to the maximum recommended 5-V power supply
the input. Although the input of the THS7365 allows
that allows approximately a ([4.9 V/2] – 0.15 V) = 2.3
for a 0-V input signal without issue, the output swing
V input range while avoiding clipping on the output.
of a traditional amplifier cannot yield a 0-V signal
resulting in possible clipping. This limitation is true for
The input impedance of the THS7365 in this mode of
any
single-supply
amplifier
because
of
the
operation
is
dictated
by
the
internal,
800-k
characteristics of the output transistors. Neither
pull-down resistor, as shown in Figure 117. Note that
CMOS nor bipolar transistors can achieve 0 V while
the internal voltage shift does not appear at the input
sinking current. This transistor characteristic is also
pin; it only shows at the output pin.
the same reason why the highest output voltage is
always less than the power-supply voltage when
sourcing current.
This output clipping can reduce the sync amplitudes
(both horizontal and vertical sync) on the video
signal. A problem occurs if the video signal receiver
uses an automatic gain control (AGC) loop to account
for losses in the transmission line. Some video AGC
circuits
derive
gain
from
the
horizontal
sync
amplitude. If clipping occurs on the sync amplitude,
then the AGC circuit can increase the gain too
much—resulting in too much luma and/or chroma
amplitude gain correction. This correction may result
in a picture with an overly bright display with too
Figure 117. Equivalent DC Input Mode Circuit
much color saturation.
34
Copyright 2009, Texas Instruments Incorporated
Product Folder Link(s): THS7365
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| THS7368IPW | 制造商:Texas Instruments 功能描述:Video Amplifier IC 制造商:Texas Instruments 功能描述:IC, VIDEO AMPLIFIER, HEX, 350MHZ TSSOP20 |
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