CXA2101AQ
5. RGB system signal processing
The RGB signals are output through the pure RGB switching, YMYS1, picture control, clamp, brightness
control, YMYS2, peak limiter, dynamic color, gamma correction, drive control and cutoff control circuits.
In the pure RGB switching circuit, the matrix selector output can be input directly to the RGB system when
RGB signals are supplied. Set MAT OUT (I2C bus) to data 3.
In YM1YS1, whether the main signals are to be toned down (YM) to 1/3 or switched (YS) to the analog RGB1
signals is set. Input the control signal to YS/YM-1 (Pin 45). Refer to the Pin Description.
Next, the signals pass through the picture control, clamp and brightness control circuits, and the signal level
and DC level are adjusted by the picture and brightness controls on which the ABL control voltage is
superimposed.
ABL operates as an average-value type.
Although similar to YS1YM1, YS2YM2 enables the level of the analog RGB2 input signals to be adjusted by
LRGB2 LEV (I2C bus).
The peak limiter operates in tandem with the brightness control: in other words, it functions only for the signal
level (100 IRE). After passing through the dynamic color, gamma correction and drive control (separate
adjustment possible for RGB) circuits, the signals are subject to cutoff control by the AKB system, and then
output to the buffer.
The dynamic color circuit increases the color temperature of the picture when 75% of the R signal level is
lower than that for G or B. The color temperature is varied up to a maximum of R : G : B = 0.97 : 1 : 1.05.
The IC contains a peak ABL circuit for suppressing excessive brightness: The peak level of the RGB output
signals is detected inside the IC and sent to the ABL circuit. Refer to the section on PABL LEV in the
description of the registers for details on the detection value. As for the feedback time constant for the actual
signals, configure a low-pass filter and attach it externally to PABL-FIL (Pin 42).
At the output stage, the bottom limiter voltage can be set by BLK-BOTTOM (I2C bus). Limiter ON/OFF can be
set by BLK-SW (I2C bus). The HV blanking level is approximately 0.1V when the limiter is set OFF. The limiter
voltage is replaced with the reference DC in each H by the RGB system and defined by the drop voltage from
that DC. The "reference DC" refers to the output DC level of REF-P for AKB. This means that the limiter
voltage is linked to the AKB status or, in other words, to the RGB-SH pin voltage. It does not depend on the
settings of the DC level control based on BRIGHT, etc. It functions for all the video signals.
The AKB system (auto cutoff function) automates the white balance (black balance) adjustment by forming a
loop between this IC and the CRT. The aging of the CRT can be compensated for by forming this loop. This
system functions using RGB-DRIVE, which adjusts the gain between the RGB outputs by I2C bus, and RGB-
CUTOFF, which adjusts the DC level.
The operation of the auto cutoff function is described next. (Refer to Fig. 1 showing the timing charts of the
REF-P output.)
• The RGB signals are shifted by 1H in sequence from R to G and from G to B at the top of the picture
(overscanning area), and the reference pulse (REF-P) for auto cutoff appears at a level of 8 IRE. Reference
pulses equivalent to 1H are output from the RGBOUT pin to the latter part of the vertical blanking period.
• These output reference pulses are detected as cathode current Ik which is then input to IKIN (Pin 41) after it
has been converted into a voltage.
• The voltage input to IKIN is compared with the reference voltage inside the IC, and the current generated by
the difference between the two voltages is sampled by the capacitor connected to the RGB-SH (Pins 40, 38
and 36) during the REF-P period. The current is held outside the REF-P period.
• The DC level of RGBOUT varies in accordance with the voltage of the RGB-SH pins. This is repeated in
each V period until the level is made equal to the reference voltage. The RGB signals each have the
reference voltage which is varied using the CUTOFF control of the I2C bus.
When this IC is used in an LCD projector, etc., it is possible to set a mode in which HV blanking is turned off.
The HV blanking and AKB system control circuits are turned off by setting the CBLK-OFF (I2C bus) data to 1.
In this mode, the RGB-OUT DC level can be adjusted by applying the voltage directly to the RGB-SH (Pins 40,
38 and 36).
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SONY [ SONY CORPORATION ]
