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? may 2002 adcs 7408392 release number 1.0 1/35 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.
AN1490 2/35 adcs 7408392 table of contents chapter 1 definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 chapter 2 g1 level control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 2.1 sub-brightness control by g1, brightness control by preamplifier ........................................ 5 2.2 sub-brightness and brightness control by g1 (method #3) .................................................. 6 2.3 g1 level control ........................................................................................................... ......... 7 chapter 3 method 1- brightness after drive, in preamplifier . . . . . . . . . . . . . . . . . . . . . . . .8 3.1 background ................................................................................................................. ......... 8 3.2 adjustment duration and performance ................................................................................. 8 3.2.1 tracking duration ........................................................................................................ ..........................................8 3.2.2 tracking performance ..................................................................................................... ......................................9 3.3 black level area calculation ............................................................................................... .11 3.4 g1 dac setting ............................................................................................................. ..... 11 3.5 stv9211 preamplifier software settings ............................................................................ 12 3.5.1 brightness is controlled by preamplifier (register 02) ................................................................... .......................12 3.5.2 brightness is after drive (register 13) .................................................................................. ..............................12 3.5.3 infra-black offset setting (register 14) ................................................................................. ...............................12 3.5.4 infra-black range setting (register 14) .................................................................................. ...............................13 3.5.5 infra-black level settings (registers 10,11,12) .......................................................................... ...........................13 3.5.6 drive setting (registers 3,4,5) .......................................................................................... ....................................13 3.6 g2 setting ................................................................................................................. .......... 13 3.7 white balance adjustment procedure ................................................................................. 13 chapter 4 method 2 - brightness before drive, in preamplifier . . . . . . . . . . . . . . . . . . . . .16 4.1 background ................................................................................................................. ....... 16 4.2 adjustment duration and performance ............................................................................... 16 4.2.1 tracking performance ..................................................................................................... ....................................16 4.2.2 tracking duration ........................................................................................................ ........................................18 4.3 black level area calculation ............................................................................................... .19 4.4 g1 dac setting ............................................................................................................. ..... 19 4.5 preamplifier stv9211 software settings ............................................................................ 20
adcs 7408392 3/35 AN1490 4.5.1 brightness is controlled by preamplifier (register 02) .................................................................. .......................20 4.5.2 brightness is before drive (register 13) ................................................................................. ..............................20 4.5.3 infra-black offset setting (register 14) ................................................................................. ................................20 4.5.4 infra-black range setting (register 14) .................................................................................. ...............................21 4.5.5 infra-black level settings (register 10,11,12) ........................................................................... ............................21 4.5.6 drive setting (registers 3,4,5) .......................................................................................... ....................................21 4.6 g2 setting ................................................................................................................. .......... 21 4.7 white balance adjustment procedure ................................................................................ 22 chapter 5 method 3 - brightness control by g1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25 5.1 background ................................................................................................................. ....... 25 5.2 adjustment duration and performance ............................................................................... 25 5.2.1 tracking duration ........................................................................................................ ........................................25 5.2.2 tracking performance ..................................................................................................... ....................................26 5.3 black level area calculation ............................................................................................... .28 5.4 g1 dac setting ............................................................................................................. ..... 28 5.5 preamplifier stv9211 software settings ............................................................................ 29 5.5.1 brightness control by g1 ................................................................................................ ...................................29 5.5.2 brightness (in preamplifier) after drive (register 13) ................................................................... .........................29 5.5.3 infra black offset setting (register 14) ................................................................................. ..............................30 5.5.4 infra-black range setting (register 14) .................................................................................. ...............................30 5.5.5 infra-black level settings (registers 10,11,12) .......................................................................... ...........................31 5.5.6 drives setting (registers 3,4,5) ......................................................................................... ...................................31 5.6 g2 setting ................................................................................................................. .......... 31 5.7 white balance adjustment procedure ................................................................................. 31 chapter 6 comparison of the three methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34
definitions AN1490 4/35 adcs 7408392 1 definitions white balance adjustment target video level requirements others y_low_lum low luminance target y_low_lum_tol tolerance of the low luminance target y_high_lum high luminance target y_high_lum_tol tolerance of the high luminance target y_abl high luminance target with a full white pattern (for abl adjustment) y_abl_tol tolerance of the high luminance target (x_target, y_target) color temperature target (x_target_tol, y_target_tol) tolerance of the color temperature target. v_contrast video range requirement (generally 40v) v_brightness brightness range requirement vdd video amplifier high voltage power sub-brightness luminance 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.
adcs 7408392 5/35 AN1490 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: l in methods 1 and 2, g1 controls only the sub-brightness. l 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. note: when controlling the brightness by preamp, v g2 -v g1 remains the same whatever the brightness. figure 1: brightness control by preamplifier, fixed g1 vdd gnd fixed g1 level = sub brightness brightness minimum brightness maximum brightness range
g1 level control AN1490 6/35 adcs 7408392 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. note: when g1 controls brightness, v g2 -v g1 decreases (respectively increases) when g1 increases (respectively decreases). consequently, v g2 -v g1 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. figure 2: brightness control by g1, variable g1 vdd gnd current g1 level -> current brightness g1 level max -> brightness max = sub brightness g1 level min -> brightness min brightness range
adcs 7408392 7/35 AN1490 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) g1 amplifier is generally a network of resistors and one transistor. figure 3: g1 circuit schematic g1 dc level dac frame blanking to the video board coupling capacitor g1 amplifier 0v to 5v t y pical -30v to -60v t y pical
method 1- brightness after drive, in preamplifier AN1490 8/35 adcs 7408392 3 method 1- brightness after drive, in preamplifier 3.1 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. 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 4: brightness after drive in preamplifier figure 5: white balance tracking of black level + drive brightness gnd gnd vdd vdd color adjustment in low luminance
adcs 7408392 9/35 AN1490 method 1- brightness after drive, in preamplifier figure 6 shows the red cathode signal before and after color tracking in high luminance. 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 6: white balance tracking of black level figure 7: red and green cathode signals - 0% brightness, 50% contrast the black level has not changed vdd vdd gnd gnd color adjustment in high luminance vdd vdd gnd gnd vred vgreen red cathode signal (red drive = 25%) green cathode signal (green drive = 50%)
method 1- brightness after drive, in preamplifier AN1490 10/35 adcs 7408392 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. 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. 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. figure 8: red and green cathode signals - 0% brightness, 100% contrast figure 9: red and green cathode signals with 10v brightness and 100% contrast red cathode signal (red drive = 25%) green cathode signal (green drive = 50%) vdd vdd gnd gnd vred vgreen gnd gnd vred vgreen 10v of brightness 10v of brightness red cathode signal (red drive = 25%) green cathode signal (green drive = 50%)
adcs 7408392 11/35 AN1490 method 1- brightness after drive, in preamplifier 3.3 black level area calculation each channel black level is set within the black level area: l black level above black level area: signal into the top non-linear area. l black level under black level area: signal into the bottom non-linear area. black level area = vdd C top non linear area (15v) C brightness C video C bottom non linear area (17v) for instance, with the following requirements: vdd =100v, v_brightness = 10v, v_contrast = 40v black level area = 100 C 15 C 10 C 40 C 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 sub- brightness. set g1 dac to its middle range as initial value . figure 10: cathode signal areas (brightness by preamplifier) figure 11: g1 dac format, brightness by preamplifier top non linear area bottom non linear area 15v black level area video brightness 17v vdd 0v vdd-15v 17v 0 g1 dac max g1 da c sub-brightness
method 1- brightness after drive, in preamplifier AN1490 12/35 adcs 7408392 3.5 stv9211 preamplifier software settings 3.5.1 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 is indicative. for more efficient infra-black offset setting, the infra-black offset is adjusted with the cathode signals: l set the 3 infra-black level registers to 0 (register 10, 11, 12). l set brightness register to 0 (register 2). l put a probe on each amplifier output. l set infra black offset so that each video black level is at least at vdd C 15v (top non linear area range). table 1: infrablack offset selection vdd (+/- 5%) infra-black offset binary decimal 112 to 115v 001 1 107 to 111v 010 2 102 to 106v 011 3 97 to 101v 100 4 92 to 96v 101 5 88 to 91v 110 6 87 and below 111 7
adcs 7408392 13/35 AN1490 method 1- brightness after drive, in preamplifier 3.5.4 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. 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: l brightness in preamplifier = brightness initial value ( section 3.5.1 ) l no video (contrast = 1) l r, g, b infrablack level = 0 (minimum) l infra black offset = infra black offset setting ( section 3.5.3 ) l 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: l initial g1 (g1 dac) = middle range l initial contrast (preamp) = 1 l initial brightness (preamplifier) = brightness initial value ( section 3.5.1 ) l infra black-offset (preamplifier) = infra black offset setting ( section 3.5.3 ) l infra black-range (preamplifier) = infra black range setting ( section 3.5.4 ) l initial infra-black level (preamplifier) = 0 l initial drive (preamplifier) = initial value of drive ( section 3.5.6 ) table 2: infra-black range selection infra black range r, g, b infra-black level step at the cathode r, g, b infra-black level range max at the cathode 0 140 mv 35.7 v 1 100 mv 25.5 v
method 1- brightness after drive, in preamplifier AN1490 14/35 adcs 7408392 table 3: summary table and instructions - method 1 step 1 waveforms description preliminary adjustment: low luminance adjustment pattern full black luminance y_low_lum instructions 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 color adjustment in low luminance pattern full black luminance y_low_lum instructions 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 low luminance checking pattern full black luminance y_low_lum instructions 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 color checking in low luminance pattern full black luminance y_low_lum instructions go to step 2 if x 1 x_targetx_target_tol and y 1 y_targety_target_tol step 5 description brightness adjustment for high luminance (optional) pattern full black luminance 0.06fl instructions adjust brightness (preamplifier) to reach y=0.06fl vdd gnd g1 vdd gnd g1 vdd gnd g1 vdd gnd g1
adcs 7408392 15/35 AN1490 method 1- brightness after drive, in preamplifier step 6 description color adjustment in high luminance pattern white box luminance y_high_lum instructions 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 high luminance checking pattern white box luminance y_high_lum instructions 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 color checking in high luminance pattern white box luminance y_high_lum instructions go to step 6 if x 1 x_target x_target_tol and y 1 y_target y_target_tol step 9 description abl setting pattern full white luminance y_abl instructions adjust abl to reach y =y_abl y_abl_tol table 3: summary table and instructions - method 1 vdd gnd g1 vdd gnd g1
method 2 - brightness before drive, in preamplifier AN1490 16/35 adcs 7408392 4 method 2 - brightness before drive, in preamplifier 4.1 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. 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 12: brightness before drive in preamplifier figure 13: red and green cathode signals with brightness minimum and contrast = 50% + drive brightness red cathode signal (red drive = 25%) green cathode signal (green drive = 50%) vdd vdd vred vgreen gnd gnd
adcs 7408392 17/35 AN1490 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. 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%) 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. figure 14: red and green cathode signals with brightness = 0v and contrast = 100% figure 15: red and green cathode signals with 5v brightness and 100% contrast red cathode signal (red drive = 25%) green cathode signal (green drive = 50%) vdd vdd vred vgreen gnd gnd red cathode signal (red drive = 25%) green cathode signal (green drive = 50%) vdd vdd vred vgreen gnd gnd
method 2 - brightness before drive, in preamplifier AN1490 18/35 adcs 7408392 4.2.2 tracking duration figure 16 shows the red cathode signal before and after color tracking in low luminance. figure 17 shows the red cathode signal before and after color tracking in high luminance. 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. figure 16: white balance tracking of black level figure 17: white balance tracking of white level vdd vdd gnd gnd color adjustment in low luminance the black level has changed vdd vdd gnd gnd color adjustment in high luminance
adcs 7408392 19/35 AN1490 method 2 - brightness before drive, in preamplifier 4.3 black level area calculation each channel black level is set within the black level area: l black level above black level area: signal into the top non-linear area. l black level under black level area: signal into the bottom non-linear area. black level area = vdd C top non linear area (15v) C brightness C video C bottom non linear area (17v) for instance, with the following requirements: vdd =100v, v_brightness = 10v, v_contrast = 40v black level area = 100 C 15 C 10 C 40 C 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. set g1 dac to its middle range as initial value . figure 18: cathode signal areas (brightness by preamplifier) figure 19: g1 dac format, brightness by preamplifier top non linear area bottom non linear area 15v black level area video brightness 17v vdd 0v vdd-15v 17v 0 g1 dac max g1 da c sub-brightness
method 2 - brightness before drive, in preamplifier AN1490 20/35 adcs 7408392 4.5 preamplifier stv9211 software settings 4.5.1 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 non- linear zone. this value depends on the vdd value: table 4 is indicative table. for more efficient infra-black offset setting, adjust the infra-black offset by checking the cathode signals: l set the 3 infra-black level registers to 0 (register 10, 11, 12). l set brightness register to 0 (register 2). l put a probe on each amplifier outputs. l set infra black offset so that each video black level is at least equal to vdd C 15v (top non linear area range). table 4: infrablack offset selection vdd (+/- 5%) infra-black offset binary decimal 112 to 115v 011 3 107 to 111v 100 4 102 to 106v 101 5 97 to 101v 110 6 92 to 96v 111 7 88 to 91v 111 7 87 and below 111 7
adcs 7408392 21/35 AN1490 method 2 - brightness before drive, in preamplifier 4.5.4 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. remark 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: l brightness in preamplifier = brightness initial value ( section 4.5.1 ) l no video (contrast = 1) l r, g, b infrablack level = 0 (minimum) l infra-black offset = infra-black offset setting ( section 4.5.3 ) l g1 dac = middle range note: check that g2, g1 levels and video signal match the tube specification (especially the spot cut-off design chart). table 5: infra black range selection infra black range r, g, b infra black level step at the cathode r, g, b infra black level range max at the cathode 0 140mv 35.7v 1 100mv 25.5v
method 2 - brightness before drive, in preamplifier AN1490 22/35 adcs 7408392 4.7 white balance adjustment procedure initial condition: l initial g1 (g1 dac) = middle range l initial contrast (preamp) = 1 l initial brightness (preamplifier) = brightness initial value ( section 4.5.1 ) l infra-black range (preamplifier) = infra-black range setting ( section 4.5.4 ) l infra-black offset (preamplifier) = infra-black offset setting ( section 4.5.3 ) l initial infra-black level (preamplifier) = 0 l initial drive (preamp) = drive initial value ( section 4.5.6 )
adcs 7408392 23/35 AN1490 method 2 - brightness before drive, in preamplifier table 6: summary table and instructions - method 2 step 1 waveforms description preliminary adjustment: low luminance adjustment pattern full black luminance y_low_lum instructions 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 color adjustment in low luminance pattern full black luminance y_low_lum instructions 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 low luminance checking pattern full black luminance y_low_lum instructions 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 color checking in low luminance pattern full black luminance y_low_lum instructions go to step 2 if x 1 x_targetx_target_tol and y 1 y_targety_target_tol step 5 description: brightness adjustment for high luminance (optional) pattern full black luminance 0.06fl instructions adjust brightness (preamplifier) to reach y=0.06fl vdd gnd g1 vdd gnd g1 vdd gnd g1 vdd gnd g1
method 2 - brightness before drive, in preamplifier AN1490 24/35 adcs 7408392 step 6 description color adjustment in high luminance pattern white box luminance y_high_lum instructions 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 luminance checking in high luminance pattern white box luminance y_high_lum instructions 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 color checking in high luminance pattern white box luminance y_high_lum instructions go to step 6 if x 1 x_target x_target_tol and y 1 y_target y_target_tol step 9 description second low and high luminance adjustment instructions go to step 1 : one extra adjustment step 10 description: abl setting pattern full white luminance y_abl instructions adjust abl to reach y =y_abl y_abl_tol table 6: summary table and instructions - method 2 vdd gnd g1 vdd gnd g1
adcs 7408392 25/35 AN1490 method 3 - brightness control by g1 5 method 3 - brightness control by g1 5.1 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 gnd gnd color adjustment in low luminance g1 g1
method 3 - brightness control by g1 AN1490 26/35 adcs 7408392 figure 21 shows the red cathode signal before and after the color tracking in high luminance. 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. 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 figure 21: white balance tracking of white level figure 22: red and green cathode signals with minimum brightness and 50% contrast the black level has not changed vdd vdd gnd gnd color adjustment in high luminance g1 g1 red cathode signal (red drive = 25%) green cathode signal (green drive = 50%) vdd vdd gnd gnd vred vgreen g1 g1
adcs 7408392 27/35 AN1490 method 3 - brightness control by g1 figure 23 shows the signals with 100% contrast. 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. 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. figure 23: red and green cathode signals with no brightness and 100% contrast figure 24: red and green cathode signals with 10v brightness and 100% contrast red cathode signal (red drive = 25%) green cathode signal (green drive = 50%) vdd vdd gnd gnd vred vgreen g1 g1 g1 g1 red cathode signal (red drive = 25%) vdd gnd vred= + 10v of brightness green cathode signal (green drive = 50%) vdd gnd 10v of brightness vgreen= +
method 3 - brightness control by g1 AN1490 28/35 adcs 7408392 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: l black level above black level area: signal into the top non-linear area. l black level under black level area: signal into the bottom non-linear area. black level area = vdd C top non linear area (15v) C video C bottom non linear area (17v) for instance, with the following requirements: vdd =100v, v_contrast = 40v black level area = 100 C 15 C 40 C 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 25: cathode signal areas (brightness by preamplifier) figure 26: g1 dac format, brightness by g1 top non linear area bottom non linear area 15v black level area video 17v vdd 0v vdd-15v 17v sub-brightness 0 g1 dac max. g1 da c brightness
adcs 7408392 29/35 AN1490 method 3 - brightness control by g1 g1 dac initial value calculation 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). 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: then we have: 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 C (171/2) = 171 set g1 dac to 171 as initial value . 5.5 preamplifier stv9211 software settings 5.5.1 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. table 7: g1 dac setting values g1 dac length g1 sub-brightness range g1 brightness range g1 min. g1 max 255 bits 20v 10v -40v -10v figure 27: g1 dac format, brightness control by g1 table 8: brightness range dac brightness range min. dac sub-brightness max dac sub-brightness 84 84 255 sub-brightness range 0 255 g1 da c 84
method 3 - brightness control by g1 AN1490 30/35 adcs 7408392 5.5.3 infra black offset setting (register 14) 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 is indicative. for more efficient infra-black offset setting, adjust the infra-black offset by checking the cathode signals: l set the 3 infra-black level registers to 0 (register 10, 11, 12). l put a probe on each amplifier outputs. l set the infra-black offset so that each video black level is at least equal to vdd C 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. 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. table 9: infrablack offset selection vdd (+/- 5%) infra-black offset binary decimal 112 to 115v 011 3 107 to 111v 100 4 102 to 106v 101 5 97 to 101v 110 6 92 to 96v 111 7 88 to 91v 111 7 87 and below 111 7 table 10: infrablack range selection infra-black range r, g, b infra-black level step at the cathode max r, g, b infra-black level range at the cathode 0 140mv 35.7v 1 100mv 25.5v
adcs 7408392 31/35 AN1490 method 3 - brightness control by g1 5.5.5 infra-black level settings (registers 10,11,12) 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: l no video (contrast = 1) l r, g, b infrablack level = 0 (minimum) l infra black offset = infra-black offset setting ( section 5.5.3 ) l 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 l initial g1 (g1 dac) = g1 dac initial value ( section 5.4 ) l initial contrast (preamplifier) = 1 l brightness (preamplifier) = 0 l infra-black range (preamplifier) = infra-black range setting ( section 5.5.4 ) l infra-black offset (preamplifier) = infra-black offset setting ( section 5.5.3 ) l initial infra-black level (preamplifier) = 0 l initial drive (preamplifier) = drive initial value ( section 5.5.6 )
method 3 - brightness control by g1 AN1490 32/35 adcs 7408392 table 11: summary table and instructions - method 3 step 1 waveforms description preliminary adjustment: low luminance adjustment pattern full black luminance y_low_lum instructions 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 color adjustment in low luminance pattern full black luminance y_low_lum instructions 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 low luminance checking pattern full black luminance y_low_lum instructions 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 color checking in low luminance pattern full black luminance y_low_lum instructions go to step 2 if x 1 x_targetx_target_tol and y 1 y_targety_target_tol step 5 description brightness adjustment for high luminance (optional) pattern full black luminance 0.06fl instructions adjust brightness (preamplifier) to reach y=0.06fl vdd gnd g1 vdd gnd g1 vdd gnd g1 vdd gnd g1
adcs 7408392 33/35 AN1490 method 3 - brightness control by g1 step 6 description color adjustment in high luminance pattern white box luminance y_high_lum instructions 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 high luminance checking pattern white box luminance y_high_lum instructions 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 color checking in high luminance pattern white box luminance y_high_lum instructions go to step 6 if x 1 x_target x_target_tol and y 1 y_target y_target_tol step 9 description abl setting pattern full white luminance y_abl instructions adjust abl to reach y=y_abl y_abl_tol table 11: summary table and instructions - method 3 vdd gnd g1 vdd gnd g1
comparison of the three methods AN1490 34/35 adcs 7408392 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 advantages drawbacks 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 ) 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
adcs 7408392 35/35 AN1490 information furnished is believed to be accurate and reliable. however, stmicroelectronics assumes no responsibility for the co nsequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of stmicroelectronics. specifications mentioned in this p ublication are subject to change without notice. this publication supersedes and replaces all information previously supplied. stmicroelectron ics products are not authorized for use as critical components in life support devices or systems without express written approval of stmicr oelectronics. the st logo is a registered trademark of stmicroelectronics ? 2002 stmicroelectronics - all rights reserved stmicroelectronics group of companies australia - brazil - canada - china - finland - france - germany - hong kong - india - israel -italy - japan - malaysia - malta - morocco - singapore - spain - sweden - switzerland - united kingdom - united states www.st.com

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