3.0 Electrical Interfaces
Fusion 878A
3.1 Input Interface
PCI Video Decoder
3-6
Conexant
100600B
3.1.8 2X Oversampling and Input Filtering
Digitized video needs to be band-limited in order to avoid aliasing artifacts.
Because the Fusion 878A samples the video data at 8
× Fsc (over twice the
normal rate), no filtering is required at the input to the A/Ds. The analog video
needs to be band-limited to 14.32 MHz in NTSC and 17.73 MHz in PAL/SECAM
mode. Normal video signals do not require additional external filtering. After
digitalization, the samples are digitally low-pass filtered and then decimated to
4 × Fsc. The response of the digital low pass filter is illustrated in
. The
digital low pass filter provides the digital bandwidth reduction to limit the video
to 6 MHz.
Figure 3-2. Clock Options
C
L
C
L
28.63636 MHz
Fundamental Crystal Oscillator
1 M
Ω
Single-Ended Oscillator
Osc
28.63636 MHz
XTI
XT
O
XTI
XT
O
no connect
XTI
XT
O
2.7
µ
H
33 pF
330 pF
22 pF
28.63636 MHz
Trap Circuit
1 M
Ω
3rd Overtone Crystal Oscillator
879A_033
Note:
Value for C
L
varies by crystal
manufacturer. Use capacitor
recommended by vendor.