AN1490
White balance adjustment procedure with ST video solutions in DC coupling mode
In a monitor, the 3 electron guns do not provide the same power. Also on the screen, red green and blue phosphors do not have the same sensibility to the electrons. More, there are gain and DC level dispersions between different amplifiers, inside the amplifier and between the 3 channels. For example, if in a monitor, blue guns are more powerful than red and green guns, the white box normally displayed with equal white and black levels finally looks a bit blue. A white balance tracking consists in: - Adjusting the R, G, B Infra-Black level register of the pre-amplifier with a black screen, this is the color adjustment in low luminance. - Adjusting the R, G, B drive registers of the pre-amplifier with a white box on screen, this is the color adjustment in high luminance. With white balance tracking, the color temperature of the displayed white box is unchanged whatever the brightness and contrast. This application note describes 3 methods to perform the white balance tracking with the ST video kit STV9211 (preamplifier) + STV955x (amplifier) (DC coupling mode): Method 1(Chapter 3): Brightness after drive in preamplifier. Method 2 (Chapter 4): Brightness before drive in preamplifier. Method 3 (Chapter 5): Brightness control by G1. The control of G1- DC level is mandatory with the ST video kit STV9211 + STV955x (Chapter 2) The method choice is related to what adjustment quality and duration the customer requires.
Chapter 6 is a summary of the 3 methods particularities.
May 2002
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Release number 1.0
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AN1490
Table of Contents
Chapter 1 Chapter 2
2.1 2.2 2.3
Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 G1 level control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
Sub-brightness control by G1, brightness control by preamplifier . . .. . .. . .. . .. . .. . .. . .. . . 5 Sub-brightness and brightness control by G1 (method #3) . . .. . .. . .. . .. . .. . .. . .. . .. . .. . . 6 G1 level control . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. 7
Chapter 3
3.1 3.2
3.2.1 3.2.2
Method 1- Brightness after drive, in preamplifier . . . . . . . . . . . . . . . . . . . . . . . .8
Background . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . ... 8 Adjustment duration and performance . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. 8
Tracking duration . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . ..8 Tracking performance . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .....9
3.3 3.4 3.5
3.5.1 3.5.2 3.5.3 3.5.4 3.5.5 3.5.6
Black level area calculation . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. 11 G1 DAC setting . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . ..... 11 STV9211 preamplifier software settings . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. 12
Brightness is controlled by preamplifier (register 02) . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .12 Brightness is after drive (Register 13) . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . ...12 Infra-black offset setting (Register 14) . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . ...12 Infra-black range setting (register 14) . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . ....13 Infra-black level settings (registers 10,11,12) . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . ..13 Drive setting (registers 3,4,5) . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . ..13
3.6 3.7
G2 setting . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .... 13 White balance adjustment procedure . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. 13
Chapter 4
4.1 4.2
4.2.1 4.2.2
Method 2 - Brightness before drive, in preamplifier . . . . . . . . . . . . . . . . . . . . .16
Background . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . . 16 Adjustment duration and performance . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . ..... 16
Tracking performance . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . ...16 Tracking duration . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .....18
4.3 4.4 4.5
Black level area calculation . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. 19 G1 DAC setting . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . ..... 19 Preamplifier STV9211 software settings . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. 20
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4.5.1 4.5.2 4.5.3 4.5.4 4.5.5 4.5.6 Brightness is controlled by preamplifier (register 02) . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .....20 Brightness is before drive (register 13) . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . ..20 Infra-black offset setting (register 14) . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . ....20 Infra-black range setting (register 14) . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . ....21 Infra-black level settings (register 10,11,12) . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . ....21 Drive setting (registers 3,4,5) . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . ..21
4.6 4.7
G2 setting . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .... 21 White Balance Adjustment procedure . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . . 22
Chapter 5
5.1 5.2
5.2.1 5.2.2
Method 3 - Brightness control by G1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
Background . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . . 25 Adjustment duration and performance . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . ..... 25
Tracking duration . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .....25 Tracking performance . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . ...26
5.3 5.4 5.5
5.5.1 5.5.2 5.5.3 5.5.4 5.5.5 5.5.6
Black level area calculation . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. 28 G1 DAC setting . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . ..... 28 Preamplifier STV9211 software settings . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. 29
Brightness control by G1 . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . ..29 Brightness (in preamplifier) after drive (register 13) . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . ...29 Infra Black Offset setting (Register 14) . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . ..30 Infra-black range setting (register 14) . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . ....30 Infra-black level settings (registers 10,11,12) . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . ..31 Drives setting (registers 3,4,5) . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .....31
5.6 5.7
G2 setting . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .... 31 White balance adjustment procedure . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. 31
Chapter 6
Comparison of the three methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34
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Definitions
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Definitions
White balance adjustment target
Y_low_lum Y_low_lum_tol Y_high_lum Y_high_lum_tol Y_ABL Y_ABL_tol (x_target, y_target) (x_target_tol, y_target_tol) low luminance target tolerance of the low luminance target high luminance target tolerance of the high luminance target high luminance target with a full white pattern (for ABL adjustment) tolerance of the high luminance target color temperature target tolerance of the color temperature target.
Video level requirements
V_Contrast V_ B right ne s s video range requirement (generally 40V) brightness range requirement
Others
VDD
Sub-Brightness luminance video amplifier high voltage power luminance when the screen is full black with maximum brightness Sub-Brightness is controlled by G1 in each method. Sub-Brightness adjusts the low luminance target.
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G1 level control
2
G1 level control
Control G1 level to perform a good white balance tracking with the ST video kit STV9211 + STV955x. The use of G1 varies with the white balance adjustment method:
q q
In methods 1 and 2, G1 controls only the sub-brightness. In method 3, G1 controls sub-brightness and brightness.
2.1
Sub-brightness control by G1, brightness control by preamplifier
This is achieved in methods 1 and 2. In this case, G1 level is adjusted during the white balance tracking to reach the low luminance target. G1 remains unchanged afterwards. The sub-brightness level is G1 fixed level.
Figure 1: Brightness control by preamplifier, fixed G1
VDD
Brightness minimum Brightness range Brightness maximum
GND
Fixed G1 level = Sub Brightness
Note:
When controlling the brightness by preamp, VG2-VG1 remains the same whatever the brightness.
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G1 level control
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2.2
Sub-brightness and brightness control by G1 (method #3)
In this case, G1 level is adjusted during the white balance tracking to reach the low luminance target. This level is related to the maximum brightness, this is also the sub-brightness level. When G1 level decreases, the brightness also decreases. The sub-brightness level corresponds to G1 level with maximum brightness.
Figure 2: Brightness control by G1, variable G1
VDD
GND
G1 level max -> Brightness max = Sub Brightness Brightness range Current G1 level -> Current Brightness G1 level min -> Brightness min
Note:
When G1 controls brightness, VG2-VG1 decreases (respectively increases) when G1 increases (respectively decreases). Consequently, VG2-VG1 decreases (respectively increases) when brightness increases (respectively decreases).
Conclusion For the same brightness level (for example 10V), the screen is brighter when preamplifiers control the brightness.
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G1 level control
2.3
G1 level control
G1 level must be DAC-controlled. Generally, G1 level is adjusted by DAC from the MCU (it can be any other I²C controlled DAC). The DAC signal (from 0V to 5V typical) is amplified to reach the required G1 DC. G1 frame blanking is coupled to G1 level by a capacitor (100nF typically)
Figure 3: G1 circuit schematic
G1 DC level DAC
0V to 5V typical
G1 amplifier
-30V to -60V typical Coupling Capacitor
To the video board
Frame Blanking
G1 amplifier is generally a network of resistors and one transistor.
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Method 1- Brightness after drive, in preamplifier
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3.1
Method 1- Brightness after drive, in preamplifier
Background
G1 is only used to adjust the sub-brightness (low luminance). Brightness is controlled by preamplifier and is adjusted after drive. With this method, tracking duration is short. After the tracking, the balance color changes with brightness.
3.2
Adjustment duration and performance
In the preamplifier, brightness is adjusted after drive, it does not depend on the drive.
Figure 4: Brightness after drive in preamplifier
Drive
+
Brightness
Changing the drive on a channel does not affect its black level: low luminance is unchanged when adjusting the color temperature in high luminance. On the other hand, after the white balance tracking, the color temperature changes with brightness adjustment.
3.2.1
Tracking duration
Figure 5 shows the red cathode signal before and after color tracking in low luminance:
Figure 5: White balance tracking of black level
VDD
VDD
Color adjustment in low luminance
GND
GND
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Method 1- Brightness after drive, in preamplifier
Figure 6 shows the red cathode signal before and after color tracking in high luminance.
Figure 6: White balance tracking of black level
VDD VDD
Color adjustment in high luminance GND
The black level has not changed
GND
Black level is unchanged: only one tracking in high and low luminance is necessary. When brightness is after drive and controlled by the preamplifier, white balance tracking is short.
3.2.2
Tracking performance
Assuming that the white balance is reached with the following drive values: red drive = 25% and green drive = 50%, Figure 7 shows the red and green cathode signals with minimum brightness and 50% contrast.
Figure 7: Red and green cathode signals - 0% brightness, 50% contrast
VDD Vred Vgreen
VDD
GND Red Cathode signal (red drive = 25%)
GND Green Cathode signal (green drive = 50%)
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Method 1- Brightness after drive, in preamplifier
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Assuming that Vred = 10V (contrast · red drive) and Vgreen = 20V (contrast green drive), the mathematical criteria for white balance is the ratio Vgreen/Vred = 2. Figure 8 represents the setting with 100% contrast.
Figure 8: Red and green cathode signals - 0% brightness, 100% contrast
VDD Vred Vgreen VDD
GND Red Cathode signal (red drive = 25%)
GND Green Cathode signal (green drive = 50%)
Contrast is proportional to the drive. When Vred = 20V (contrast · red drive) and Vgreen = 40V (contrast · green drive), the ratio Vgreen/Vred = 2 is unchanged. The white balance is reached for the contrast part of the video signal. When brightness is after drive and controlled by the preamplifier, the color temperature does not change when changing the contrast.
Figure 9 shows the signals with 10V of brightness.
Figure 9: Red and green cathode signals with 10V brightness and 100% contrast
10V of brightness
Vred Vgreen
10V of brightness
GND Red Cathode signal (red drive = 25%)
GND Green Cathode signal (green drive = 50%)
Brightness does not depend on the drive. With Vred = 30V (brightness + contrast · red drive) and Vgreen = 50V (brightness + contrast · green drive), Vgreen/Vred = 1.6, the ratio has changed The white balance is not reached for the brightness part of the video signal. When brightness is after drive and controlled by the preamplifier, the color temperature changes when changing the brightness. Conclusion When brightness is after drive and controlled by the preamplifier, the color temperature remains unchanged with contrast adjustment but it is sensitive to brightness.
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Method 1- Brightness after drive, in preamplifier
3.3
Black level area calculation
Each channel black level is set within the black level area:
q q
Black level above black level area: signal into the top non-linear area. Black level under black level area: signal into the bottom non-linear area.
Figure 10: Cathode signal areas (brightness by preamplifier)
VDD Top Non Linear Area 15V VDD-15V Black level area Brightness
Video
17V Bottom Non Linear Area 17V 0V
Black level area =
VDD top non linear area (15V) brightness video bottom non linear area (17V) For instance, with the following requirements: VDD =100V, V_Brightness = 10V, V_Contrast = 40V Black level area = 100 15 10 40 17 = 18V The black area stands between 67V and 85V.
3.4
G1 DAC setting
Brightness is controlled by preamplifier, so the full range of G1 DAC is used to adjust the subbrightness.
Figure 11: G1 DAC format, Brightness by preamplifier
G1 DAC 0
Sub-Brightness
G1 DAC max
Set G1 DAC to its middle range as initial value.
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3.5
3.5.1
STV9211 preamplifier software settings
Brightness is controlled by preamplifier (register 02)
The brightness DAC resolution is 8mV and the amplifier gain = 20. Brightness DAC maximum value is V_Brightness / (8mV * 20) which also corresponds to brightness DAC initial value. For example, if V_Brightness is 10V, brightness DAC maximum value is 63.
3.5.2
Brightness is after drive (Register 13)
Register 13 (bandwidth adjustment) bit 6 is set to 1: brightness after drive.
3.5.3
Infra-black offset setting (Register 14)
The infra black offset (register 14, Bit 1,2,3) value is set to avoid the video signal from going in the top non-linear zone, it is related to VDD value.
Table 1: Infrablack offset selection Infra-black offset VDD (+/- 5%) Binary
112 to 115V 107 to 111V 102 to 106V 97 to 101V 92 to 96V 88 to 91V 87 and below 001 010 011 100 101 110 111
Decimal
1 2 3 4 5 6 7
Table 1 is indicative. For more efficient infra-black offset setting, the infra-black offset is adjusted with the cathode signals:
q q q q
Set the 3 infra-black level registers to 0 (register 10, 11, 12). Set brightness register to 0 (register 2). Put a probe on each amplifier output. Set infra black offset so that each video black level is at least at VDD 15V (top non linear area range).
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Method 1- Brightness after drive, in preamplifier
Infra-black range setting (register 14)
Register 14 (bit 0) fixes R, G, B infra black level range and also the step of the R, G, B infra-black level DACs.
Table 2: Infra-black range selection Infra black range
0 1
R, G, B infra-black level step at the cathode
140 mV 100 mV
R, G, B infra-black level range max at the cathode
35.7 V 25.5 V
Note:
Do not set the infra black level registers with too high values otherwise the black level is below the black level area.
For instance, with the previous requirements (Section 3.3), and with infra-black range =1 (step=100mV), the infra-black level maximum value is: black level area/step = 18V/100mV = 180.
3.5.5
Infra-black level settings (registers 10,11,12)
Set every infra-black level registers to 0 as initial values.
3.5.6
Drive setting (registers 3,4,5)
Drive register initial values must be as close as possible to Y_high_lum and (x_target, y_target) values for the fastest tracking. These values are determined during a manual white balance tracking in a reference monitor. Generally, initial drive values are equal and only related to Y_high_lum.
3.6
G2 setting
G2 is set by hardware on a reference monitor to reach Y = Y_low_lum with the following conditions:
q q q q q
Brightness in preamplifier = brightness initial value (Section 3.5.1) No video (contrast = 1) R, G, B Infrablack level = 0 (minimum) Infra Black Offset = Infra Black Offset setting (Section 3.5.3) G1 DAC = middle range
Note:
check that the levels of G2, G1, and Video signal match the tube specification (especially the spot cut-off design chart).
3.7
White balance adjustment procedure
Initial condition:
q q q q q q q
Initial G1 (G1 DAC) = middle range Initial contrast (preamp) = 1 Initial brightness (preamplifier) = brightness initial value (Section 3.5.1) Infra black-offset (preamplifier) = Infra black offset setting (Section 3.5.3) Infra black-range (preamplifier) = infra black range setting (Section 3.5.4) Initial Infra-black level (preamplifier) = 0 Initial drive (preamplifier) = initial value of drive (Section 3.5.6)
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Method 1- Brightness after drive, in preamplifier
Table 3: Summary table and instructions - method 1
Step 1 Description Pattern Luminance Instructions Preliminary adjustment: low luminance adjustment full black Y_low_lum set contrast to 1 set brightness to initial value adjust sub brightness (G1) so that Y=Y_low_lum Y_low_lum_tol Step 2 Description Pattern Luminance Instructions Color adjustment in low luminance full black Y_low_lum Adjust R, G, B Infra Black level to reach x=x_target x_target_tol and y=y_target y_target_tol Find the dominant color. The Infra Black level of this dominant color will be fixed. Increase the 2 others Infra Black levels to reach x=x_target x_target_tol and y=y_target y_target_tol. Step 3 Description Pattern Luminance Instructions Low luminance checking full black Y_low_lum If Y is different from Y_low_lum Y_low_lum_tol, adjust G1 (sub-brightness) to reach Y =Y_low_lum Y_low_lum_tol Step 4 Description Pattern Luminance Instructions Step 5 Description Pattern Luminance Instructions Brightness adjustment for high luminance (optional) full black 0.06FL Adjust brightness (Preamplifier) to reach Y=0.06FL Color checking in low luminance full black Y_low_lum Go to step 2 if x x_targetx_target_tol and y y_targety_target_tol Waveforms
AN1490
VDD
GND G1
VDD
GND G1
VDD
GND G1
VDD
GND G1
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Method 1- Brightness after drive, in preamplifier
Table 3: Summary table and instructions - method 1
Step 6 Description Pattern Luminance Instructions Color adjustment in high luminance White box Y_high_lum Set contrast to 255 Adjust R, G, B Drive to reach x=x_target x_target_tol and y=y_target y_target_tol: Find the dominant color. The Drive of this dominant color will be fixed. Increase the 2 others Drives to reach x=x_target x_target_tol and y= y_target y_target_tol. Step 7 Description Pattern Luminance Instructions High luminance checking White box Y_high_lum If Y is different from Y_high_lum Y_high_lum_tol, adjust simultaneously R, G, B Drives to reach Y = Y_high_lum Y_high_lum_tol. Step 8 Description Pattern Luminance Instructions Step 9 Description Pattern Luminance Instructions ABL setting Full white Y_ ABL Adjust ABL to reach Y =Y_ABL Y_ABL_tol Color checking in high luminance White box Y_high_lum Go to step 6 if xx_target x_target_tol and yy_target y_target_tol
GND G1 VDD
VDD
GND G1
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Method 2 - Brightness before drive, in preamplifier
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4.1
Method 2 - Brightness before drive, in preamplifier
Background
G1 only adjusts the sub-brightness (low luminance). Brightness is controlled by preamplifier and brightness is before drive. Tracking performances are very good: the color temperature is unchanged whatever the brightness or contrast. However, tracking duration is long.
4.2
Adjustment duration and performance
As brightness is before drive in the preamplifier, it is proportional to the drive.
Figure 12: Brightness before drive in preamplifier
+
Drive
Brightness
Following the white balance tracking, the color temperature is unchanged whatever the brightness or contrast. Especially, the color temperature in high luminance (white) does not change with brightness. On the other hand, changing the drive on a channel affects its black level: the low luminance and color temperature in low luminance change when adjusting the color temperature in high luminance.
4.2.1
Tracking performance
Assuming that white balance is reached with the following drive values: red drive = 25% and green drive = 50%, Figure 13 shows red and green cathode signals with minimum brightness.
Figure 13: red and green cathode signals with brightness minimum and contrast = 50%
VDD Vred Vgreen VDD
GND Red Cathode signal (red drive = 25%)
GND Green Cathode signal (green drive = 50%)
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Method 2 - Brightness before drive, in preamplifier
Assuming that Vred = 10V (contrast · red drive) and Vgreen = 20V (contrast · green drive), the mathematical criteria of white balance is the ratio Vgreen/Vred = 2.
Figure 14 shows the signals while setting the contrast to maximum.
Figure 14: red and green cathode signals with brightness = 0V and contrast = 100%
VDD
VDD
Vred Vgreen
GND Red Cathode signal (red drive = 25%)
GND Green Cathode signal (green drive = 50%)
Contrast is proportional to the drive. Vred = 20V (contrast · red drive) and Vgreen = 40V (contrast · green drive), the ratio Vgreen/Vred = 2 has not changed. The white balance is reached for the contrast part of the video signal. When brightness is before drive and controlled by the preamplifier, the color temperature does not change with the contrast.
Figure 15 shows the resulting signals when adding 5V of brightness in red signal. Brightness being proportional to the drive, 10V of brightness has been added to the green signal (10V · 50%/25%)
Figure 15: red and green cathode signals with 5V brightness and 100% contrast
VDD
VDD
Vred
Vgreen GND Red Cathode signal (red drive = 25%) GND Green Cathode signal (green drive = 50%)
Brightness is proportional to the drive. Vred = 30 [(brightness + contrast) · red drive] and Vgreen = 60 [(brightness + contrast) · red drive], the ratio Vgreen/Vred = 2 has not changed. The white balance is reached for the brightness part of the video signal. When brightness is before drive and controlled by the preamplifier, the color temperature does not vary with brightness. Conclusion When brightness is before drive and controlled by the preamplifier, the color temperature does not change with brightness and contrast.
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Method 2 - Brightness before drive, in preamplifier 4.2.2 Tracking duration
Figure 16 shows the red cathode signal before and after color tracking in low luminance.
Figure 16: White balance tracking of black level
AN1490
VDD
VDD
Color adjustment in low luminance
GND
GND
Figure 17 shows the red cathode signal before and after color tracking in high luminance.
Figure 17: White balance tracking of white level
VDD VDD
Color adjustment in high luminance
The black level has changed
GND
GND
Note:
The black level has changed: a second tracking in low and high luminance is necessary. During the second high luminance adjustment, the black level does not change significantly.
Conclusion When brightness is before drive and controlled by preamplifier, white balance tracking is long.
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Method 2 - Brightness before drive, in preamplifier
4.3
Black level area calculation
Each channel black level is set within the black level area:
q q
Black level above black level area: signal into the top non-linear area. Black level under black level area: signal into the bottom non-linear area.
Figure 18: Cathode signal areas (brightness by preamplifier)
VDD Top Non Linear Area 15V VDD-15V Black level area Brightness
Video
17V Bottom Non Linear Area 17V 0V
Black level area =
VDD top non linear area (15V) brightness video bottom non linear area (17V) For instance, with the following requirements: VDD =100V, V_Brightness = 10V, V_Contrast = 40V Black level area = 100 15 10 40 17 = 18V The black area stands between 67V and 85V.
4.4
G1 DAC setting
Brightness is controlled by preamplifier, G1 DAC full range is used to adjust the sub-brightness.
Figure 19: G1 DAC format, brightness by preamplifier
G1 DAC 0
Sub-Brightness
G1 DAC max
Set G1 DAC to its middle range as initial value.
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4.5
4.5.1
Preamplifier STV9211 software settings
Brightness is controlled by preamplifier (register 02)
Brightness being proportional to the drive, brightness DAC resolution in a channel depends on this channel drive value. The amplifier gain is 20. The brightness maximum step (for drive =254) is 8mV*20 = 160mV. Brightness step = 160*(drive value/254) mV. Brightness DAC maximum value is V_Brightness / brightness step. For example, if V_Brightness is 10V and drive = 127, the maximum value of brightness DAC is 125.
4.5.2
Brightness is before drive (register 13)
Set bit 6 of register 13 (bandwidth adjustment) to 0: brightness before drive.
4.5.3
Infra-black offset setting (register 14)
Set the infra-black offset (register 14 - bits 1,2,3) so that video signal does not go into the top nonlinear zone. This value depends on the VDD value:
Table 4: Infrablack offset selection Infra-black offset VDD (+/- 5%) Binary
112 to 115V 107 to 111V 102 to 106V 97 to 101V 92 to 96V 88 to 91V 87 and below 011 100 101 110 111 111 111
Decimal
3 4 5 6 7 7 7
Table 4 is indicative table. For more efficient infra-black offset setting, adjust the infra-black offset by checking the cathode signals:
q q q q
Set the 3 infra-black level registers to 0 (register 10, 11, 12). Set brightness register to 0 (register 2). Put a probe on each amplifier outputs. Set infra black offset so that each video black level is at least equal to VDD 15V (top non linear area range).
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AN1490 4.5.4
Method 2 - Brightness before drive, in preamplifier
Infra-black range setting (register 14)
Bit 0 of register 14 fixes the range of the R, G, B infra-black level and also the step of the R, G, B infra-black level DACs.
Table 5: Infra Black range selection Infra Black Range
0 1
R, G, B Infra Black level step at the cathode
140mV 100mV
R, G, B Infra Black level range max at the cathode
35.7V 25.5V
R e mark Make sure infra-black level registers values are not too high so that black level is not below the black level area (Section 4.3). For instance, with the previous requirements from Section 4.3 and with infra-black range =1 (step=100mV), the infra-black level maximum value is black level area/step = 18V/100mV = 180.
4.5.5
Infra-black level settings (register 10,11,12)
Set every infra-black level registers to 0 as initial values.
4.5.6
Drive setting (registers 3,4,5)
Set the drive register initial values as close as possible to Y_high_lum and (x_target, y_target) values for the fastest tracking. These values are determined during a manual white balance tracking in a reference monitor. Generally, the drive initial values are equal and determined to match only Y_high_lum.
4.6
G2 setting
G2 is set by hardware on a reference monitor to reach Y =Y_low_lum with the following conditions:
q q q q q
Brightness in preamplifier = brightness initial value (Section 4.5.1) No video (contrast = 1) R, G, B infrablack level = 0 (minimum) Infra-black offset = Infra-black offset setting (Section 4.5.3) G1 DAC = middle range
Note:
check that G2, G1 levels and Video signal match the tube specification (especially the spot cut-off design chart).
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Method 2 - Brightness before drive, in preamplifier
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4.7
White Balance Adjustment procedure
Initial condition:
q q q q q q q
Initial G1 (G1 DAC) = middle range Initial contrast (preamp) = 1 Initial brightness (preamplifier) = brightness initial value (Section 4.5.1) Infra-black range (preamplifier) = infra-black range setting (Section 4.5.4) Infra-black offset (preamplifier) = infra-black offset setting (Section 4.5.3) Initial infra-black level (preamplifier) = 0 Initial drive (preamp) = drive initial value (Section 4.5.6)
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Method 2 - Brightness before drive, in preamplifier
Table 6: Summary table and instructions - method 2
Step 1 Description Pattern Luminance Instructions Preliminary adjustment: low luminance adjustment full black Y_low_lum set contrast to 1 set brightness to initial value adjust sub brightness (G1) so that Y=Y_low_lum Y_low_lum_tol Step 2 Description Pattern Luminance Instructions Color adjustment in low luminance full black Y_low_lum Adjust R, G, B Infra Black level to reach x=x_target x_target_tol and y=y_target y_target_tol Find the dominant color. The Infra Black level of this dominant color will be fixed. Increase the 2 others Infra Black levels to reach x = x_target x_target_tol and y = y_target y_target_tol. Step 3 Description Pattern Luminance Instructions Low luminance checking full black Y_low_lum If Y is different from Y_low_lum Y_low_lum_tol, adjust G1 (sub-brightness) to reach Y = Y_low_lum Y_low_lum_tol Step 4 Description Pattern Luminance Instructions Step 5 Description: Pattern Luminance Instructions Brightness adjustment for high luminance (optional) full black 0.06FL Adjust brightness (Preamplifier) to reach Y=0.06FL Color checking in low luminance full black Y_low_lum Go to step 2 if x x_targetx_target_tol and y y_targety_target_tol
Waveforms
VDD
GND G1
VDD
GND G1
VDD
GND G1
VDD
GND G1
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Method 2 - Brightness before drive, in preamplifier
Table 6: Summary table and instructions - method 2
Step 6 Description Pattern Luminance Instructions Color adjustment in high luminance White box Y_high_lum Set contrast to 255 Adjust R, G, B Drive to reach x=x_target x_target_tol and y=y_target y_target_tol: Find the dominant color. The Drive of this dominant color will be fixed. Increase the 2 others Drives to reach x=x_target x_target_tol and y= y_target y_target_tol. Step 7 Description Pattern Luminance Instructions Luminance checking in high luminance White box Y_high_lum If Y is different from Y_high_lum Y_high_lum_tol, adjust simultaneously R, G, B Drives to reach Y= Y_high_lum Y_high_lum_tol. Step 8 Description Pattern Luminance Instructions Step 9 Description Instructions Step 10 Description: Pattern Luminance Instructions ABL setting Full white Y_ ABL Adjust ABL to reach Y =Y_ABL Y_ABL_tol Second low and high luminance adjustment Go to step 1: one extra adjustment Color checking in high luminance White box Y_high_lum Go to step 6 if xx_target x_target_tol and yy_target y_target_tol
AN1490
VDD
GND G1
VDD
GND G1
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Method 3 - Brightness control by G1
5
5.1
Method 3 - Brightness control by G1
Background
G1 is used to adjust sub-brightness and brightness. Tracking duration is short however, the balance color changes with brightness after the tracking.
5.2
Adjustment duration and performance
Brightness is controlled by G1: the brightness versus drive behavior is the same as in Chapter 3: method 1 - Brightness control by preamplifier and after drive. As explained in Chapter 3, the low luminance (and the color temperature) does not change when adjusting the color temperature in high luminance. On the other hand, color temperature changes with the brightness after the white balance tracking.
5.2.1
Tracking duration
Figure 20 shows the red cathode signal before and after the color tracking in low luminance.
Figure 20: White balance tracking of black level
VDD
VDD
Color adjustment in low luminance
GND
GND
G1
G1
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Method 3 - Brightness control by G1
AN1490
Figure 21 shows the red cathode signal before and after the color tracking in high luminance.
Figure 21: White balance tracking of white level
VDD VDD
Color adjustment in high luminance The black level has not GND changed
GND
G1
G1
The black level does not changed, only one tracking in high and low luminance is necessary. When G1 controls the brightness, the white balance tracking is fast.
5.2.2
Tracking performance
We assume that the white balance is reached with the following drive values: red drive = 25% and green drive = 50%.
Figure 22 shows the red and green cathode signals with minimum brightness and 50% contrast.
Figure 22: red and green cathode signals with minimum brightness and 50% contrast
VDD
VDD
Vred Vgreen
GND
GND
G1 Red Cathode signal (red drive = 25%)
G1 Green Cathode signal (green drive = 50%)
In the case where Vred = 10V (contrast · red drive) and Vgreen = 20V (contrast green drive), the mathematical criteria of white balance for the brightness part of the video signal is the ratio Vgreen/Vred = 2
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Figure 23 shows the signals with 100% contrast.
Method 3 - Brightness control by G1
Figure 23: red and green cathode signals with no brightness and 100% contrast
VDD
VDD
Vred Vgreen
GND
GND
G1 Red Cathode signal (red drive = 25%)
G1 Green Cathode signal (green drive = 50%)
Contrast is proportional to drive. Vred = 20V (contrast · red drive) and Vgreen = 40V (contrast · green drive), Vgreen/Vred = 2, the ratio has not changed. The white balance is reached in the contrast part of the video signal. When G1 controls the brightness, the color temperature does not change with contrast.
Figure 24 shows the signals resulting from the addition of 10V to brightness.
Figure 24: red and green cathode signals with 10V brightness and 100% contrast
VDD
VDD
Vred= + GND G1 10V of Brightness
Vgreen= + GND G1 10V of Brightness Green Cathode signal (green drive = 50%)
Red Cathode signal (red drive = 25%)
Then Vred = 30V (brightness + contrast · red drive) and Vgreen = 50V (brightness + contrast · green drive), Vgreen/Vred = 1.6, the ratio has changed. The white balance is not reached in the brightness part of the video signal. When G1 controls brightness, the color temperature varies with brightness adjustments.
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Method 3 - Brightness control by G1
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Conclusion When G1 controls the brightness, the color temperature does not change with contrast but it is sensitive to brightness adjustment.
5.3
Black level area calculation
Each channel black level is set within the black level area:
q q
Black level above black level area: signal into the top non-linear area. Black level under black level area: signal into the bottom non-linear area.
Figure 25: Cathode signal areas (brightness by preamplifier)
VDD Top Non Linear Area 15V VDD-15V Black level area
Video
17V Bottom Non Linear Area 17V 0V
Black level area = VDD top non linear area (15V) video bottom non linear area (17V)
For instance, with the following requirements: VDD =100V, V_Contrast = 40V Black level area = 100 15 40 17 = 28V The black area stands between 57V and 85V.
5.4
G1 DAC setting
G1 controls brightness and sub-brightness. One part of G1 DAC range is used for the brightness, the rest is used for sub-brightness.
Figure 26: G1 DAC format, brightness by G1
Brightnes s
G1 DAC 0
Sub-Brightness
G1 DAC max.
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AN1490 G1 DAC initial value calculation
Method 3 - Brightness control by G1
Calculate the G1 DAC initial value by taking into account the brightness range. The following example shows G1 DAC initial value calculation with typical values of brightness and sub-brightness ranges. We assume that G1 level increases with G1 DAC (the luminance increases with G1 DAC).
Table 7: G1 DAC setting values G1 DAC length
255 bits
G1 sub-brightness range
20V
G1 brightness range
10V
G1 min.
-40V
G1 max
-10V
G1 total range is 20+10 = 30V G1 step is: 30V/255 = 118mV. The DAC range for brightness is then: 10/0.118 = 84 So sub-brightness stands between 84 and 255:
Figure 27: G1 DAC format, brightness control by G1
Sub-Brightness range
G1 DAC 0
84
255
Then we have:
Table 8: Brightness range DAC brightness range
84
min. DAC sub-brightness
84
max DAC Sub-brightness
255
The white balance adjustment determines the maximum brightness setting. The low luminance adjustment initial value is set with the medium value of sub-brightness range: 255 (171/2) = 171 Set G1 DAC to 171 as initial value.
5.5
5.5.1
Preamplifier STV9211 software settings
Brightness control by G1
Set the preamplifier brightness DAC (register 2) to 0 and never change it.
5.5.2
Brightness (in preamplifier) after drive (register 13)
Set bit 6 of register 13 (Bandwidth adjustment) to 1: brightness after drive.
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Method 3 - Brightness control by G1 5.5.3 Infra Black Offset setting (Register 14)
AN1490
Set the infra-black offset (register 14, bits 1,2,3) to the correct value so that the video signal is not in the top non-linear zone. This value depends on VDD value.
Table 9: Infrablack offset selection Infra-black offset VDD (+/- 5%) Binary
112 to 115V 107 to 111V 102 to 106V 97 to 101V 92 to 96V 88 to 91V 87 and below 011 100 101 110 111 111 111
Decimal
3 4 5 6 7 7 7
Table 9 is indicative. For more efficient infra-black offset setting, adjust the infra-black offset by checking the cathode signals:
q q q
Set the 3 infra-black level registers to 0 (register 10, 11, 12). Put a probe on each amplifier outputs. Set the infra-black offset so that each video black level is at least equal to VDD 15V (top non linear area range).
5.5.4
Infra-black range setting (register 14)
Infra-black range (register 14, bit 0) fixes the R, G, B infra-black level range, and also the step of the R, G, B infra black level DACs.
Table 10: Infrablack range selection Infra-black range
0 1
R, G, B infra-black level step at the cathode
140mV 100mV
max R, G, B infra-black level range at the cathode
35.7V 25.5V
Avoid setting the infra-black level registers with too high values so that the black level is not below the black level area (Section 5.3). For instance, with the previous requirements (Section 5.3), and with Infra-black range =1 (step=100mV), the maximum value of infra-black level will be: black level area/step = 18V/100mV = 180.
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Method 3 - Brightness control by G1
Set every infra-black level registers to 0 as initial values.
5.5.6
Drives setting (registers 3,4,5)
Set the drive register initial values as close as possible to Y_high_lum and (x_target, y_target) values for the fastest tracking. Those values are determined during a manual white balance tracking in a reference monitor. Generally, the initial drive values are equal and determined to match only Y_high_lum value.
5.6
G2 setting
G2 is set by hardware on a reference monitor to reach Y = Y_low_lum with the following conditions:
q q q q
No video (contrast = 1) R, G, B Infrablack level = 0 (minimum) Infra Black Offset = Infra-black offset setting (Section 5.5.3) G1 DAC = G1 DAC initial value (Section 5.4)
Note:
Check that the levels of G2, G1 and video signal match the tube specification (especially the spot cut-off design chart).
5.7
White balance adjustment procedure
Initial condition
q q q q q q q
Initial G1 (G1 DAC) = G1 DAC initial value (Section 5.4) Initial contrast (preamplifier) = 1 Brightness (preamplifier) = 0 Infra-black range (preamplifier) = infra-black range setting (Section 5.5.4) Infra-black offset (preamplifier) = infra-black offset setting (Section 5.5.3) Initial Infra-black level (preamplifier) = 0 Initial drive (preamplifier) = drive initial value (Section 5.5.6)
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Method 3 - Brightness control by G1
Table 11: Summary table and instructions - method 3
Step 1 Description Pattern Luminance Instructions Preliminary adjustment: low luminance adjustment full black Y_low_lum set contrast to 1 set brightness to initial value adjust sub brightness (G1) so that Y=Y_low_lum Y_low_lum_tol Step 2 Description Pattern Luminance Instructions Color adjustment in low luminance full black Y_low_lum Adjust R, G, B Infra Black level to reach x=x_target x_target_tol and y=y_target y_target_tol Find the dominant color. The Infra Black level of this dominant color will be fixed. Increase the 2 others Infra Black levels to reach x=x_target x_target_tol and y=y_target y_target_tol. Step 3 Description Pattern Luminance Instructions Low luminance checking full black Y_low_lum If Y is different from Y_low_lum Y_low_lum_tol, adjust G1 (sub-brightness) to reach Y = Y_low_lum Y_low_lum_tol Step 4 Description Pattern Luminance Instructions Step 5 Description Pattern Luminance Instructions Brightness adjustment for high luminance (optional) full black 0.06FL Adjust brightness (Preamplifier) to reach Y=0.06FL Color checking in low luminance full black Y_low_lum Go to step 2 if x x_targetx_target_tol and y y_targety_target_tol
G1 GND
AN1490
Waveforms
VDD
VDD
GND G1
VDD
GND G1
VDD
GND G1
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Method 3 - Brightness control by G1
Table 11: Summary table and instructions - method 3
Step 6 Description Pattern Luminance Instructions Color adjustment in high luminance White box Y_high_lum Set contrast to 255 Adjust R, G, B Drive to reach x=x_target x_target_tol and y=y_target y_target_tol: Find the dominant color. The Drive of this dominant color will be fixed. Increase the 2 others Drives to reach x=x_target x_target_tol and y= y_target y_target_tol. Step 7 Description Pattern Luminance Instructions High luminance checking White box Y_high_lum If Y is different from Y_high_lum Y_high_lum_tol, adjust simultaneously R, G, B Drives to reach Y=Y_high_lum Y_high_lum_tol. Step 8 Description Pattern Luminance Instructions Step 9 Description Pattern Luminance Instructions ABL setting Full white Y_ ABL Adjust ABL to reach Y=Y_ABL Y_ABL_tol Color checking in high luminance White box Y_high_lum Go to step 6 if xx_target x_target_tol and yy_target y_target_tol
GND G1 VDD
GND VDD
G1
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Comparison of the three methods
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6
Comparison of the three methods
We assume the same sub-brightness range (20V) and G1 DAC size for the 3 methods.
Table 12: Advantages and drawbacks of the 3 methods Method Method 1
Brightness after drive, controlled by preamplifier Short tracking (Section 3.2.1) Small step of sub-brightness and brightness Color temperature changes with brightness (Section 3.5.1) Small black level area (Section 3.3)
Advantages
Drawbacks
Method 2
Brightness before drive, controlled by preamplifier Same color temperature whatever the contrast or brightness (Section 4.2.1) Small step of sub-brightness and brightness Long tracking (Section 4.2.2) Small black level area (Section 4.3)
Method 3
Brightness controlled by G1 Short tracking (Section 5.2.1) Large black level area (Section 5.3) Color temperature changes with brightness (Section 5.5.1) Large step of sub-brightness and brightness
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