參數(shù)資料
型號(hào)： THS7375IPW
廠商： TEXAS INSTRUMENTS INC
元件分類： 音頻／視頻放大
英文描述： VIDEO AMPLIFIER, PDSO14
封裝： GREEN, PLASTIC, TSSOP-14
文件頁(yè)數(shù)： 19/39頁(yè)
文件大小： 973K
代理商： THS7375IPW
SBOS449A – SEPTEMBER 2008 – REVISED JANUARY 2011
www.ti.com
LOW-PASS FILTER
Keep in mind that images do not stop at the DAC
sampling frequency, fS (for example, 27 MHz for
Each
channel
of
the
THS7375
incorporates
a
traditional SD DACs); they continue around the
sixth-order low-pass filter. These video reconstruction
sampling frequencies of 2X fS, 3X fS, 4X fS, etc. (54
filters minimize the passing of DAC images to the
MHz, 81 MHz, 108 MHz). Because of these multiple
video receiver. Depending on the receiver design,
images that an ADC can fold down into the baseband
failure to eliminate these DAC images can cause
signal, the low-pass filter must also eliminate these
picture quality problems as a result of ADC aliasing.
higher
order
images.
The
THS7375
filters
are
Another benefit of the filter is to smooth out
Butterworth filters and as such, do not bounce at
aberrations in the signal that some DACs can have if
higher frequencies and maintain good attenuation
the internal device filtering is not very good. This
performance.
technique helps with picture quality and helps ensure
that the signal meets video bandwidth requirements.
The 9.5-MHz filter frequency was chosen to account
for process variations in the THS7375. To ensure that
Each
filter
has
an
associated
Butterworth
the required video frequencies are effectively passed,
characteristic.
The
benefit
of
the
Butterworth
the filter corner frequency must be high enough to
response is that the frequency response is flat, with a
allow component variations. The other consideration
relatively steep initial attenuation at the corner
is that the attenuation must be large enough to
frequency. The problem with this characteristic is that
ensure the anti-aliasing/reconstruction filtering is
the group delay rises near the corner frequency.
adequate to meet the system demands. Thus, the
Group delay is defined as the change in phase
filter frequencies were not arbitrarily selected and are
(radians/second) divided by a change in frequency.
a good compromise that should meet the demands of
An increase in group delay corresponds to a time
most systems.
domain pulse response that has overshoot and some
possible ringing associated with the overshoot.
Benefits Over Passive Filtering
The use of other type of filters, such as elliptic or
Two key benefits of using an integrated filter system
chebyshev,
are
not
recommended
for
video
such as the THS7375 over a passive system are
applications because of the very large group delay
PCB area and filter variations. The small TSSOP-14
variations near the corner frequency that results in
package for four video channels is much smaller over
significant overshoot and ringing. While these elliptic
a passive RLC network, especially a six-pole passive
or chebyshev filters may help meet the video
network. Additionally, consider that inductors have at
standard specifications with respect to amplitude
best ±10% tolerances (normally ±15% to ±20% are
attenuation, the group delay is well beyond the
common)
and
capacitors
typically
have
±10%
standard specifications. When considering these filter
tolerances. Using a Monte Carlo analysis shows that
types, keep in mind that video can go from a white
the filter corner frequency (–3 dB), flatness (–1 dB), Q
pixel to a black pixel over and over again, and ringing
factor (or peaking), and channel-to-channel delay
can easily occur. Ringing typically causes a display to
have wide variations. This approach can lead to
have ghosting or fuzziness appear on the edges of a
potential
performance
and
quality
issues
in
sharp transition. On the other hand, a Bessel filter
mass-production environments. The THS7375 solves
has ideal group delay response, but the rate of
most of these problems with the corner frequency
attenuation is typically too slow for acceptable image
being essentially the only variable.
rejection. Thus, the Butterworth filter is a respectable
compromise for both attenuation and group delay.
Another concern about passive filters is the use of
inductors. Inductors are magnetic components and
The THS7375 filters have a nominal corner (–3 dB)
are
therefore
susceptible
to
electromagnetic
frequency at 9.5 MHz and a –1-dB passband typically
coupling/interference
(EMC/EMI).
Some
common
at 8 MHz. This 9.5-MHz filter is ideal for standard
coupling can occur because of other nearby video
definition (SD) NTSC, PAL, and SECAM composite
channels that use inductors for filtering, or it can
video (CVBS) signals. It is also useful for s-video
come from nearby switched-mode power supplies.
signals (Y'C'), 480i/576i Y'P'BP'R, Y'U'V', broadcast
Some other forms of coupling could be from outside
G'B'R' (R'G'B') signals, and computer video signals.
sources with strong EMI radiation that can cause
The 9.5-MHz, –3-dB corner frequency was designed
failure in EMC testing such as required for CE
to achieve 54 dB of attenuation at 27 MHz—a
compliance.
common sampling frequency between the DAC/ADC
second and third Nyquist zones found in many video
One concern about an active filter in an integrated
systems. This consideration is important because any
circuit is the variation of the filter characteristics when
signal that appears around this frequency can also
the ambient temperature and the subsequent die
appear in the baseband as the result of aliasing
temperature
change.
To
minimize
temperature
effects of an ADC found in a receiver.
effects,
the
THS7375
uses
low
temperature
coefficient resistors and high-quality/low-temperature
coefficient capacitors found in the BiCom3X process.
26
Copyright 2008–2011, Texas Instruments Incorporated
Product Folder Link(s): THS7375
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參數(shù)描述
THS7375IPWG4 功能描述:視頻放大器 4Ch SDTV Video Amp w/6th order fltr 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
THS7375IPWR 功能描述:視頻放大器 4Ch SDTV 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
THS7375IPWRG4 功能描述:視頻放大器 4Ch SDTV Video Amp w/6th order fltr 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
THS7376 制造商:TI 制造商全稱:Texas Instruments 功能描述:4-Channel Video Amplifier with One SD and Three HD 8th-Order Filters with 6-dB Gain
THS7376IPW 制造商:Texas Instruments 功能描述:4-Channel Video Amplifier 1SD 3HD 制造商:Texas Instruments 功能描述:IC SDTV VIDEO AMP 4-CH 14-TSSOP
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