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參數(shù)資料
| 型號： | BT864AKPF |
| 英文描述： | Color Encoder Circuit |
| 中文描述： | 顏色編碼器電路 |
| 文件頁數(shù)： | 64/76頁 |
| 文件大小： | 1050K |
| 代理商： | BT864AKPF |
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3.0 PC Board Considerations
Bt864A/865A
3.5 Applications Information
YCrCb to NTSC/PAL Digital Video Encoder
3-8
Conexant
100138B
3.5.5 Filtering RF Modulator Connection
The Bt864A/865A internal upsampling filter alleviates external filtering
requirements by moving significant sampling alias components above 19 MHz
and reducing the sinx/x aperture loss up to the filter
’
s passband cutoff of 5.75
MHz. While typical chrominance subcarrier decoders can handle the
Bt864A/865A output signals without analog filtering, the higher frequency alias
products pose some EMI concerns and may create troublesome images when
introduced to an RF modulator. When the video is presented to an RF modulator,
it should be free of energy in the region of the aural subcarrier (4.5 MHz for
NTSC, 5.5
–
6.5 MHz for PAL), hence some additional frequency traps may be
necessary when the video signal contains fundamental or harmonic energy (as
from unfiltered character generators) in that region. For example, a pixel rate of
13.5 msps is three times the NTSC-M aural carrier of 4.5 MHz, hence significant
harmonic energy can fall on the FM aural carrier for character cell sizes which are
multiples of three. Where better frequency response flatness is required, some
peaking in the analog filter is appropriate to compensate for residual digital filter
losses with sufficient margin to tolerate 10% reactive components.
A three-pole elliptic filter (1 inductor, 3 capacitors) with a 6.75 MHz
passband can provide at least 45 dB attenuation (including sinx/x loss) of
frequency components above 20 MHz and provide some flexibility for mild
peaking or special traps. An inductor value with a self-resonant frequency above
80 MHz is chosen so that its intrinsic capacitance contributes less than 10% of the
total effective circuit value. The inductor itself may induce 1% (0.1 dB) loss, and
worst case subcarrier attenuation (including sinx/x loss) may be 7% with 10%
tolerance reactive components. Any additional ferrites introduced for EMI control
after termination should have less than 5
impedance below 5 MHz to minimize
additional losses. The capacitor to ground at the Bt864A/865A output pin is
compensated for the parasitic capacitance of the chip plus any protection diodes
and lumped circuit traces (about 22 pF+5 pF/diode). Some filter peaking can be
accomplished by splitting the source impedance across the reactive PI filter
network. However, this will also introduce some chrominance-luminance delay
distortion in the range of 10
–
20 ns for a maximum of 0.5 dB boost at the
subcarrier frequency.
The filter network feeding an RF modulator may include the aforementioned
trap, which could take two forms depending on the depth of attenuation and type
of resonator device employed. The RF modulator typically has a high input
impedance (about 1 K
± 30%) and loose tolerance. Consequently, the amplitude
variation at the modulator input will be greater, especially when the trap is
properly terminated at the modulator input for maximum effect. Some modulators
video or aural fidelity will degrade dramatically when overdriven, so the value of
the effective termination (nominally 37.5
) may need to be adjusted downward
to maintain sufficient linearity (or depth of modulation margin) in the RF signal.
Where required to maintain better than 40 dB audio dynamic range in the
presence of video energy in the region of the aural carrier, a two section trap with
more than 20 dB attenuation may be warranted. Best gain flatness versus
frequency and luma-chroma delay match can be obtained by active buffering and
use of the variable luma delay on CVBS/B channel. See
Figure 3-2
.
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| BT864AKRF | 制造商:CONEXANT 制造商全稱:CONEXANT 功能描述:YCrCb to NTSC/PAL Digital Video Encoder |
| BT864KPF | 制造商:BT 功能描述:COLOR SIGNAL ENCODER, PQFP52 |
| BT864KPF-ES1 | 制造商:BT 功能描述:864KPF-ES1 |
| BT865A | 制造商:CONEXANT 制造商全稱:CONEXANT 功能描述:High Performance YCrCb to NTSC/PAL Digital Video Encoders |
| BT865AKPF | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Color Encoder Circuit |
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