saa4961 NXP Semiconductors, saa4961 Datasheet - Page 7

• Manufacturer Part Number: saa4961
• Description: Saa4961 Integrated Multistandard Comb Filter
• Manufacturer: NXP Semiconductors

Philips Semiconductors
SYS1
System switch input signals to adapt the signal processing
to the different CVBS standards.
Table 9 System switch input signals
Note
1. The standard PAL B, G, H, D and I is internally preset
REFDL (
Decoupling capacitor for the delay line reference voltage.
COMBENA (
Output signal that indicates the current mode of operation.
This output is forced to LOW if the comb filter is in
BYPASS-mode.
Table 10 Mode of operation
Internal functional description
S
Delays the CVBS input signal by 2 lines and 4 lines
(all PAL standards) or by 1 line and 2 lines (NTSC
standard). Input signals for the delay lines are the CVBS
signal, the clock CL3 (3
the standard selection signal SYSPAL.
Output signals are the non-delayed, the 2-line delayed and
the 4-line delayed CVBS signal (PAL) or the 1-line delayed
and the 2-line delayed CVBS signal (NTSC).
S
The comb filter input BPFs attenuate the low frequencies
to guarantee a correct signal processing within the logical
comb filter.
1997 Feb 03
LOW
LOW
HIGH
HIGH
LOW
HIGH
WITCHED CAPACITOR DELAY LINE
WITCHED CAPACITOR
SYS1
Integrated multistandard comb filter
as default.
COMBENA
AND
PIN
LOW
HIGH
LOW
HIGH
SYS2 (
SYS2
24)
PIN
25)
PINS
PAL M
PAL B, G, H, D and I; note 1
NTSC M
PAL N
BYPASS-mode; PLL and clock
processing stopped
COMB-mode
B
20
AND
f
AND
sc
-P
), the control signal HSEL and
SELECTED MODE
ASS
23)
STANDARD
F
ILTERS
(BPF
S
)
7
The comb filter output BPF reduces the alias components
that are the result of the non-linear signal processing within
the logical comb filter.
L
Separates the chrominance from the band-pass filtered
CVBS signal.
C
Compensates the internal processing time of the
band-pass filters and the logical comb filter section.
A
The comb filtered luminance output signal is obtained by
adding the delayed CVBS signal and the inverted comb
filtered chrominance signal.
L
Analog input low-pass filter to reduce the outband
frequencies of EMC. The input low-pass filter is included in
the signal path but it can be switched off via the input
signal LPFION.
L
Two different types of output low-pass filters (LPFO1 and
LPFO2) are necessary to get equal signal delays within the
luminance path and the chrominance path (important for
good transient behaviour). The low-pass output filter type
LPFO1 is used for the luminance output while LPFO2 is
used for the chrominance output. The filters are analog 3rd
order elliptic low-pass filters that convert the output signals
from the time discrete to the time continuous domain
(reconstruction filter).
LPF
Automatic tuning of the low-pass filters is achieved by
adjusting the filter delays. The control information for all
filters (CONT1 and CONT2) is derived from a built-in
reference filter (LPFO1-type) that is part of a control loop.
The control loop tunes the reference filter delay and thus
all other filter delays to a time constant derived from the
system clock CL3.
C
The control and clock processing block (see Fig.9)
consists of the sub-blocks PLL, the clock processing and
the mode control. The PLL and the clock processing are
released for operation if the input level at BYP selects the
COMB-mode.
OGICAL COMB FILTER
OW
OW
DDER
OMPENSATION DELAY
ONTROL AND CLOCK PROCESSING
-
-
CONTROL
PASS
PASS
F
F
ILTER
ILTER
I
O
NPUT
UTPUTS
(LPFI)
(LPFO1
Preliminary specification
(CLOCK CONTROL)
AND
LPFO2)
SAA4961