saa4996h NXP Semiconductors, saa4996h Datasheet - Page 17

• Manufacturer Part Number: saa4996h
• Description: Motion Adaptive Colour Plus And Control Ic Macpacic For Palplus
• Manufacturer: NXP Semiconductors

Philips Semiconductors
The frame integration part can be preset with the first
measured value. Preset is controlled via a bit from the
SNERT interface.
7.10
The automatic gain and offset control circuit evaluates the
results of the reference data, which are derived from
reference lines 22, 23 and 623 to eliminate any offset and
gain differences between the letter box lines and the
helper lines. This is caused during transmission of the
video signal.
7.10.1
MacpOn: If line 22 is not detected this bit will be ignored
and the MACP processing (and thus AGC and AOC) is
switched off.
FilmOn: If line 22 is not detected, the VERIC operates in
Camera mode.
HlpM1, HlpM0: In adaptive and fixed helper processing
modes (HlpM1 = 1, HlpM0 = X) AGC and AOC are
achieve.
Table 1 Control bits HlpM1 and HlpM0
7.10.2
If line 22 reference is present in a frame, the luminance
input signal contains black set-up and reduced amplitude.
The luminance gain then is 1.25. If line 22 is not valid the
luminance gain is 1.0.
The helper gain is controlled by the measured helper
amplitude in line 23 to match the helper amplitude to the
decompanding table. After decompanding the helper
amplitude is controlled by the measured luminance
amplitude in line 623, to obtain the correct
luminance/helper ratio for the QMF filter in the VERIC.
1996 Oct 28
HlpM1
Motion Adaptive Colour Plus And Control
IC (MACPACIC) for PALplus
0
0
1
1
Automatic gain and offset control
SNERT
AOC
G
AIN CONTROL
HlpM0
0
1
0
1
CONTROL BITS INFLUENCING THE
no helper processing
(any aspect ratio, without helper)
helper set to zero
(up-conversion without helper)
adaptive helper processing (helper
processing controlled by reference
amplitudes and noise in the helper
channel)
fixed helper processing (fixed gain
values loaded via SNERT-bus)
FUNCTION
AGC
AND
17
The helper amplitude is reduced when the measured noise
exceeds a certain threshold level. These thresholds are
conveyed via the SNERT-bus. The reduction of the helper
amplitude, before decompanding, ensures that more noise
is cancelled by the coring. The adaptive helper gain control
is switched off when the SNERT bits HlpM1 and HlpM0 are
both at logic 1. In this condition the helper gain is defined
by the values FixHlp and FixMain via the SNERT-bus.
If the measured helper or luminance amplitude is below
the threshold level, or when line 22 is not valid, the helper
is switched off.
7.10.3
As long as line 22 reference is present, luminance and
helper offset are controlled by line 22. If line 22 is not valid
the offset value is fixed to 16.
For luminance offset control a hysteresis function,
controlled by SNERT, is applied to the measured
luminance offset.
7.10.4
In the event of noisy helper signals the helper amplitude
and bandwidth can be reduced to avoid disturbances in
the inverse QMF processing in VERIC.
Five thresholds are therefore transmitted via SNERT.
These thresholds are compared with the measured helper
noise value. The results are used to control a state
machine with five states.
The state machine is initialized with the preset bit from
SNERT or when line 22 is valid for the first time.
The output states are used to control the helper amplitude
and bandwidth as shown in Fig.8 and Tables 2 and 3.
7.11
Luminance lines: straight binary, black = 16, white = 191.
PALplus helper lines: offset binary, 128 70.
Output range
O
H
ELPER AMPLITUDE AND BANDWIDTH CONTROL
FFSET CONTROL
Preliminary specification
SAA4996H