EP1437709A1 - Procédé et dispositif de stabilisation du contraste d'un affichage par rapport aux variations dépendant de température - Google Patents

Procédé et dispositif de stabilisation du contraste d'un affichage par rapport aux variations dépendant de température Download PDF

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Publication number
EP1437709A1
EP1437709A1 EP20030000453 EP03000453A EP1437709A1 EP 1437709 A1 EP1437709 A1 EP 1437709A1 EP 20030000453 EP20030000453 EP 20030000453 EP 03000453 A EP03000453 A EP 03000453A EP 1437709 A1 EP1437709 A1 EP 1437709A1
Authority
EP
European Patent Office
Prior art keywords
display
frequency
local oscillator
output signal
temperature
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP20030000453
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German (de)
English (en)
Inventor
Siegmar Buhl
Willy Graf
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Siemens AG
Original Assignee
Siemens AG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Siemens AG filed Critical Siemens AG
Priority to EP20030000453 priority Critical patent/EP1437709A1/fr
Priority to PCT/EP2003/014189 priority patent/WO2004064032A1/fr
Publication of EP1437709A1 publication Critical patent/EP1437709A1/fr
Withdrawn legal-status Critical Current

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    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
    • G09G3/36—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using liquid crystals
    • G09G3/3611—Control of matrices with row and column drivers
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2320/00—Control of display operating conditions
    • G09G2320/02—Improving the quality of display appearance
    • G09G2320/0285—Improving the quality of display appearance using tables for spatial correction of display data
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2320/00—Control of display operating conditions
    • G09G2320/04—Maintaining the quality of display appearance
    • G09G2320/041—Temperature compensation
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2320/00—Control of display operating conditions
    • G09G2320/06—Adjustment of display parameters
    • G09G2320/066—Adjustment of display parameters for control of contrast

Definitions

  • the invention relates to a method and device for stabilizing a display against temperature dependent contrast variations, said display being controlled by display drive signals including a temperature dependent contrast control signal generated by a display controller being timed with an output signal of a local oscillator, such display in particular being a liquid crystal display (LCD).
  • display drive signals including a temperature dependent contrast control signal generated by a display controller being timed with an output signal of a local oscillator, such display in particular being a liquid crystal display (LCD).
  • LCD liquid crystal display
  • displays such as LCDs
  • a contrast input voltage that is used to vary the contrast in order to allow adjustment at a wanted predetermined contrast setpoint.
  • the voltage required to obtain such contrast setting depends amongst others on the display temperature.
  • a temperature sensor may be positioned in direct contact with or integrated into the display itself, such as known from European Patent Application 0 244 510. This allows on the one hand for an accurate temperature measurement, but requires on the other hand special and therewith costly production and handling facilities.
  • a more cost effective, but less accurate, method of temperature measurement is applied in other conventional display systems, in which a temperature sensor is located on a printed circuit board separated from the display.
  • the invention is characterized by said contrast control signal varying with temperature dependent frequency variations of said local oscillator output signal.
  • the local oscillator varies in its oscillation frequency with temperature and along therewith the frequency of all clocksignals derived from the oscillator output signal. This normally unwanted phenomenon is now used in accordance with the invention to determine the display temperature.
  • the display temperature is determined by measuring or detecting the actual frequency of the local oscillator output signal directly, or indirectly through one of the clocksignals derived therefrom. This not only removes the need for a separate dedicated temperature sensor such as used in the above conventional LCD drivers but also allows for a cost effective and simple implementation, in particular when said frequency detection is applied to a low frequency clock signal.
  • a method according to the invention is preferably characterized by said contrast control signal varying with a clocksignal being derived from said local oscillator output signal through frequency division.
  • Such frequency division may already be applied to obtain proper synchronization in generating display drive signals, such as display column and row control signals or master-slave synchronization. This removes the need for an extra dedicated frequency divider.
  • the invention is characterized by said contrast control signal being derived from a temperature dependent frequency reference curve being calibrated by actual measurement of display temperature and frequency of said local oscillator output signal. This allows for an optimization in the accuracy of temperature measurement, which takes into account device-to-device tolerance deviation dependent frequency variations of the local oscillator output signal.
  • said local oscillator is preferably being implemented as an RC oscillator.
  • the invention also relates to a display driving device being arranged for implementing a method as claimed in Claim 1.
  • FIG. 1 shows a block diagram of a display system 1-5 including a display driving device 1-4 and providing display drive signals to a display 5 for proper operation thereof, such display preferably being a liquid crystal display (LCD).
  • the display driving device 1-4 comprises a display controller 1 using a microcontroller, which in generating said display drive signals, is clock synchronized with an output signal of a local oscillator, as will be further clarified with reference to Figure 2.
  • the display controller 1 is provided with a contrast control input receiving through a contrast control signal line 4, a contrast control signal VLCD from a contrast control signal generating circuit 3, for adjusting the display contrast.
  • the contrast control signal VLCD varies with temperature such, that temperature dependent deviations from a predetermined display contrast setting are compensated, therewith obtaining dynamic contrast stabilisation.
  • the display system of Figure 1 described so far corresponds in function and operation to conventional type display systems such as the above cited LCD drivers. For further details in this respect, reference is made to these known LCD drivers.
  • the display driving device 1-4 of Figure 1 implements the method according to the invention in that the temperature dependent contrast control signal VLCD is generated without using a dedicated temperature sensor to measure the display temperature, but a frequency detector.
  • the display temperature is measured by detecting the frequency of the local oscillator output signal itself, i.e. directly, or indirectly by detecting the frequency of one of the clock signals which are derived from said local oscillator output signal. Any change in display temperature will cause the frequency of the local oscillator to change and along therewith also the output signal of said frequency detector, as will be explained in more detail with reference to Figure 5.
  • the frequency detector is included in the contrast control signal generating circuit 3 and is being supplied with said local oscillator output signal or said one of the clocksignals from the display controller 1 through signal line 2.
  • the frequency detector may be implemented by means of a microcontroller detecting or "reading" the frequency of the local oscillator output signal or said one of the clocksignals when being supplied to its frequency signal input.
  • the frequency detector or microcobtroller provides a detection signal varying with temperature dependent frequency variations of said local oscillator output signal (f OSC2 ), which in accordance with the invention is used to vary said contrast control signal VLCD with the detected frequency variations such, that an appropriate contrast stabilisation against display temperature variations is obtained.
  • FIG. 2 shows a detailed functional diagram of a part of the display controller 1 of Figure 1, showing a master-slave configuration which on itself is known from the above conventional LCD drivers.
  • a master device 6 comprises an internal local RC oscillator 8 having a frequency determining resistor Rf coupled externally to this master device 6 through oscillator terminals OSC2 and OSC1.
  • the oscillator characteristics and oscillator frequency of RC oscillators depend strongly of the temperature, therewith making such oscillator type in particular suitable to implement the invention.
  • the oscillator terminal OSC2 is coupled through a local oscillator signal line to oscillator terminal OSC2' of a slave device 7 to supply thereto the local oscillator output signal f OSC2 .
  • FIG 3 shows a general block diagram of a conventional large scale integrated (LSI) LCD driver circuit showing in broader context locations and/or terminals carrying the local oscillator output signal or clocksignals derived from said local oscillator output signal.
  • LSI large scale integrated
  • the LSI LCD driver circuit includes amongst others, a display timing generator DTG, providing at its interface connections easy external access to the local oscillator output signal f OSC2 , the frame synchronisation signal FR or any other synchronisation signal derived from said local oscillator output signal.
  • a display timing generator DTG providing at its interface connections easy external access to the local oscillator output signal f OSC2 , the frame synchronisation signal FR or any other synchronisation signal derived from said local oscillator output signal.
  • Figure 4 shows timing diagrams illustrating a frame synchronisation signal FR derived by frequency division from a Common Master timing signal MC and a Common Slave timing signal SC clock signal, which in their turn are clocksynchronized with the local oscillator output signal f OSC2 .
  • a selection can be made for the frame signal between a duty of 1/16 or 1/32 of the duty cycle of said common timing signals.
  • the frame synchronisation signal FR and the Common Master and Common Slave timing signal MC and SC, respectively, are fully synchronous with the local oscillator output signal f OSC2 and allow to use a simple frequency detector for frequency detection due to their relatively low frequency.
  • Figure 5 shows a signal plot illustrating with curve I a typical temperature dependent frequency variation of a display controller clock signal within a temperature range from - 40° C to + 80° C.
  • Curve I shows a decrease in frequency at increasing temperature, which is approximately linear and shows a relative variation in frequency between minimum and maximum limits within this temperature range, exceeding 20%.
  • Curve II shows the variation in frequency of a crystal oscillator output signal relative to a nominal frequency within the same temperature range, which is almost flat.
  • Curve I may be obtained by measuring the actual frequency of a local oscillator output signal or a clocksignal derived therefrom, for reason of simplicity in the aggregate also being referred to as local oscillator output signal f OSC2 , at various temperatures of the display and may be used as reference curve for calibration by actual frequency measurement at predetermined reference temperature values, as will be explained hereinafter with reference to Figure 6.
  • Figure 6 shows a flow chart of a method for calibrating display temperature stabilisation according to the invention in a series of display driving devices, or more in particular LCD drivers, which are subject to device-to-device tolerance deviations.
  • the contrast control signal is being derived from a temperature dependent frequency reference curve being calibrated by actual frequency measurement of said local oscillator output signal f OSC2 at predetermined reference temperature values as follows.
  • curve I of a first display driving device is measured as describe above and the temperature frequency correlation of this reference curve I within a practically chosen temperature range is being stored in the form of a fixed table in a non-volatile memory of a second display driving device , which is to be calibrated in its automatic contrast control.
  • non volatile memory may be an EEPROM positioned on the printed circuit board next to the main micro controller. Due to device-to-device tolerance deviations, the temperature frequency correlation of this second display driving device deviates from that of the reference display driving device.
  • the temperature frequency correlation of this calibrated curve I is being stored in a fixed table of the non-volatile memory of the second display driving device, e.g. by overwriting the originally stored temperature frequency correlation of the reference curve I, or by using a further fixed table.
  • This table is used in operation as a frequency-temperature conversion table allowing to converse each frequency value f within the temperature range of interest immediately into its corresponding temperature value T.
  • This temperature value T is further processed to obtain in on itself known manner a contrast control signal stabilising appropriately the display contrast against display temperature variations.
  • FIG 7 is a graphical presentation of a calibration set up for calibration of the temperature dependent frequency reference curve I as shown in Figure 5 to the specifics of an LCD driving device, in the foregoing being referred to as second display driving device.
  • the LCD driving device comprises an LCD controller with internal local oscillator 9 positioned at or onto the LCD and being connected to a microcontroller 3, also being referred to as main microcontroller, mounted on a printed circuit board (PCB) 16. Also mounted on the PCB 16 is a non-volatile memory 15 containing initially the above mentioned temperature dependent frequency reference curve I.
  • the calibration set up includes a temperature sensor 18, such as an infrared thermometer, measuring the actual display temperature and supplying this temperature data through line 20 to a host computer 17.
  • the microcontroller 3 detects or measures the frequency of the output signal of the internal local oscillator 9 occurring at the measured actual display temperature and supplies this frequency data through line 20 to the host computer 17.
  • the host computer 17 compares the so measured temperature-frequency correlation with the corresponding temperature-frequency correlation of the temperature dependent frequency reference curve I. Any deviation between the measured actual values on the one hand and the corresponding reference values on the other hand will cause the host computer to shift or offset the temperature dependent frequency reference curve I such that the initial deviation is fully cancelled.
  • the so obtained new curve is fully matched to the specific deviation spread of this LCD driving device and is stored in the non-volatile memory 15 for immediate conversion of frequency data into temperature data, needed for temperature stabilization of display contrast in accordance with the invention.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • General Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Liquid Crystal Display Device Control (AREA)
  • Liquid Crystal (AREA)
  • Control Of Indicators Other Than Cathode Ray Tubes (AREA)
EP20030000453 2003-01-10 2003-01-10 Procédé et dispositif de stabilisation du contraste d'un affichage par rapport aux variations dépendant de température Withdrawn EP1437709A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
EP20030000453 EP1437709A1 (fr) 2003-01-10 2003-01-10 Procédé et dispositif de stabilisation du contraste d'un affichage par rapport aux variations dépendant de température
PCT/EP2003/014189 WO2004064032A1 (fr) 2003-01-10 2003-12-10 Procede et dispositif assurant la stabilisation d'un afficheur contre les variations du contraste dependant de la temperature

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP20030000453 EP1437709A1 (fr) 2003-01-10 2003-01-10 Procédé et dispositif de stabilisation du contraste d'un affichage par rapport aux variations dépendant de température

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EP1437709A1 true EP1437709A1 (fr) 2004-07-14

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WO (1) WO2004064032A1 (fr)

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS63249825A (ja) * 1987-04-06 1988-10-17 Seiko Epson Corp 液晶素子の駆動方法
JPS63257725A (ja) * 1987-04-15 1988-10-25 Nec Corp 液晶表示器駆動電圧の温度補償回路
DE4239522A1 (de) * 1992-11-25 1994-05-26 Vdo Schindling Verfahren und Anordnung zur Erfassung der Temperatur mindestens eines Bauteils
JPH0943626A (ja) * 1995-08-02 1997-02-14 Sharp Corp 光書き込み型空間光変調装置
JP2000009547A (ja) * 1998-06-22 2000-01-14 Hitachi Ltd 温度センサおよびそれを用いた液晶表示装置並びに投写型液晶表示装置
WO2000036583A2 (fr) * 1998-12-14 2000-06-22 Kopin Corporation Systeme de micro-affichage portable
EP1158484A2 (fr) * 2000-05-25 2001-11-28 Seiko Epson Corporation Traitement de données d'image fournies à un dispositif d'affichage

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS51128296A (en) * 1975-05-01 1976-11-09 Seiko Instr & Electronics Ltd Indicator
CH637474A5 (fr) * 1979-06-07 1983-07-29 Bioself Int Inc Thermometre electronique.
US4923285A (en) * 1985-04-22 1990-05-08 Canon Kabushiki Kaisha Drive apparatus having a temperature detector
US6496177B1 (en) * 2000-02-24 2002-12-17 Koninklijke Philips Electronics N.V. Liquid crystal display (LCD) contrast control system and method
TWI234134B (en) * 2000-04-14 2005-06-11 Koninkl Philips Electronics Nv Display driver with double calibration means

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS63249825A (ja) * 1987-04-06 1988-10-17 Seiko Epson Corp 液晶素子の駆動方法
JPS63257725A (ja) * 1987-04-15 1988-10-25 Nec Corp 液晶表示器駆動電圧の温度補償回路
DE4239522A1 (de) * 1992-11-25 1994-05-26 Vdo Schindling Verfahren und Anordnung zur Erfassung der Temperatur mindestens eines Bauteils
JPH0943626A (ja) * 1995-08-02 1997-02-14 Sharp Corp 光書き込み型空間光変調装置
JP2000009547A (ja) * 1998-06-22 2000-01-14 Hitachi Ltd 温度センサおよびそれを用いた液晶表示装置並びに投写型液晶表示装置
WO2000036583A2 (fr) * 1998-12-14 2000-06-22 Kopin Corporation Systeme de micro-affichage portable
EP1158484A2 (fr) * 2000-05-25 2001-11-28 Seiko Epson Corporation Traitement de données d'image fournies à un dispositif d'affichage

Non-Patent Citations (4)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN vol. 013, no. 059 (P - 826) 10 February 1989 (1989-02-10) *
PATENT ABSTRACTS OF JAPAN vol. 013, no. 073 (P - 830) 20 February 1989 (1989-02-20) *
PATENT ABSTRACTS OF JAPAN vol. 1997, no. 06 30 June 1997 (1997-06-30) *
PATENT ABSTRACTS OF JAPAN vol. 2000, no. 04 31 August 2000 (2000-08-31) *

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