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參數資料
| 型號： | THS7368IPW |
| 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, TSSOP-20 |
| 文件頁數： | 22/40頁 |
| 文件大小： | 1123K |
| 代理商： | THS7368IPW |
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www.ti.com
SBOS497 – DECEMBER 2009
–3-dB corner frequency was designed to achieve 54
BENEFITS OVER PASSIVE FILTERING
dB of attenuation at 27 MHz—a common sampling
Two key benefits of using an integrated filter system,
frequency between the DAC/ADC second and third
such as the THS7368, over a passive system are
Nyquist zones found in many video systems. This
PCB area and filter variations. The small TSSOP-20
consideration is important because any signal that
package for six video channels is much smaller over
appears around this frequency can also appear in the
a passive RLC network, especially a six-pole passive
baseband as a result of aliasing effects of an ADC
network. Additionally, consider that inductors have at
found in a receiver.
best ±10% tolerances (normally, ±15% to ±20% is
The THS7368 SF filters have a nominal corner
common)
and
capacitors
typically
have
±10%
(–3 dB) frequency at 9.5 MHz, 18 MHz, 36 MHz, or
tolerances. Using a Monte Carlo analysis shows that
72 MHz and a –1-dB passband typically at 8.2 MHz,
the filter corner frequency (–3 dB), flatness (–1 dB), Q
16 MHz, 30 MHz, or 60 MHz. The 9.5-MHz filter is
factor (or peaking), and channel-to-channel delay
ideal for component 480i or 576i video. The 18-MHz
have wide variations. These variances can lead to
filter is ideal for component 480p or 576p component
potential
performance
and
quality
issues
in
video. The 36-MHz filter is ideal for HD 720p, 1080i,
mass-production environments. The THS7368 solves
1080p24, or 1080p30 component video. The 72-MHz
most of these problems with the corner frequency
filter is ideal for 1080p50 or 1080p60 component
being essentially the only variable.
video. These filters can also be utilized for some
Another concern about passive filters is the use of
computer R’G’B’ video signals including VGA, SVGA,
inductors. Inductors are magnetic components, and
XGA, SXGA, and QXGA.
are
therefore
susceptible
to
electromagnetic
Keep in mind that images do not stop at the DAC
coupling/interference
(EMC/EMI).
Some
common
sampling frequency, fS (for example, 27 MHz for
coupling can occur because of other video channels
traditional SD DACs); they continue around the
nearby using inductors for filtering, or it can come
sampling frequencies of 2x fS, 3x fS, 4x fS, and so on
from nearby switched-mode power supplies. Some
(that is, 54-MHz, 81-MHz, 108-MHz, etc.). Because of
other forms of coupling could be from outside sources
these multiple images, an ADC can fold down into the
with strong EMI radiation and can cause failure in
baseband signal, meaning that the low-pass filter
EMC testing such as required for CE compliance.
must also eliminate these higher-order images. The
One concern about an active filter in an integrated
THS7368 filters are Butterworth filters and, as such,
circuit is the variation of the filter characteristics when
do not bounce at higher frequencies, thus maintaining
the ambient temperature and the subsequent die
good attenuation performance.
temperature
changes.
To
minimize
temperature
The filter frequencies were chosen to account for
effects,
the
THS7368
uses
low-temperature
process variations in the THS7368. To ensure the
coefficient resistors and high-quality, low-temperature
required video frequencies are effectively passed, the
coefficient capacitors found in the BiCom3X process.
filter corner frequency must be high enough to allow
These filters have been specified by design to
component variations. The other consideration is that
account for process variations and temperature
the attenuation must be large enough to ensure the
variations to maintain proper filter characteristics.
anti-aliasing/reconstruction filtering is sufficient to
This approach maintains a low channel-to-channel
meet the system demands. Thus, the selection of the
time delay that is required for proper video signal
filter frequencies was not arbitrarily selected and is a
performance.
good compromise that should meet the demands of
Another benefit of the THS7368 over a passive RLC
most systems.
filter is the input and output impedance. The input
One of the features of the THS7368 is that these
impedance presented to the DAC varies significantly,
filters can be bypassed. Bypassing the SD filters
from 35
to over 1.5 k with a passive network, and
results in an amplifier with 150-MHz bandwidth and
may cause voltage variations over frequency. The
125-V/
μs slew rate. This configuration can be helpful
THS7368 input impedance is 800 k
, and only the
when diagnosing potential system issues or when
2-pF
input
capacitance
plus
the
PCB
trace
simply wishing to pass higher frequency signals
capacitance impact the input impedance. As such,
through the system.
the voltage variation appearing at the DAC output is
better controlled with a fixed termination resistor and
Bypassing the SF filters results in a amplifier
the high input impedance buffer of the THS7368.
supporting 375-MHz bandwidth and 600-V/
μs slew
rate. This configuration supports computer R'G'B'
On the output side of the filter, a passive filter again
signals up to UWXGA resolution.
has a large impedance variation over frequency. The
EIA770 specifications require the return loss to be at
least 25 dB over the video frequency range of usage.
For a video system, this requirement implies the
Copyright 2009, Texas Instruments Incorporated
29
Product Folder Link(s): THS7368
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相關代理商/技術參數 |
參數描述 |
|---|---|
| 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 |
| THS7368IPWR | 功能描述:視頻放大器 6-Ch 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 |
| THS7371IPW | 制造商:Texas Instruments 功能描述:VIDEO OPAM - Rail/Tube |
| THS7371IPWR | 制造商:Texas Instruments 功能描述:VIDEO OPAM - Tape and Reel |
| THS7372 | 制造商:TI 制造商全稱:Texas Instruments 功能描述:4-Channel Video Amplifier with One CVBS and Three Full-HD Filters with 6-dB Gain |
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