DISPLAY DRIVER WITH DOUBLE CALIBRATION MEANS

Abstract: A display driver device with double calibration allows the manufacturer of the display driver device to correct the manufacturing process related spread of parameters by storing basic settings, while the manufacturer of display modules can store correction factors to tailor the characteristics of a display module containing a particular display driver device and a particular display device.

Description: Display dπver with double calibration means The present invention relates to a dπver circuit for a display device including a means for stoπng a basic setting of an adjustable characteπstic of the dπver circuit The present invention also relates to a method of adjusting an individual property of a display module containing a display device and a dπver circuit connected to this display device Such a dπver circuit for a display device is known from the data sheet of the integrated circuit PCF 2103 the 1998 Philips Data Handbook IC03a 'semiconductors for wired telecom systems' In order to properly dπve an LCD display, the dπver circuit must provide multiple waveforms at a certain multiplex rate, where the waveforms also have specific bias levels The known dπver circuit includes an LCD bias voltage generator, which can be programmed to adapt the LCD bias voltage to the display device chosen to obtain optimal optical performance from the LCD Display Most LCD display devices require the off voltage of the dπve signal to remain below a certain lower threshold, while the on-voltage must exceed a certain higher threshold in order to yield an acceptable contrast. Since both the lower and higher thresholds depend on temperature, viewing angle and display device, the user is provided with a contrast control to adjust the characteπstics of the dπver circuit, so that they match the characteπstics of the display device Characteπstics of the LCD display that can be adjusted to yield optimal optical quality are contrast and transparency The contrast control is necessary because of spreads in the manufactuπng process of both the dπver circuit and the display device Also different models of display devices exhibit different characteπstics A disadvantage of the known dπver circuit for a display device is that, as a result of the manufactuπng spread, the setting of the dπver circuit is not optimized for the display device to which it is to be connected and that, therefore, a contrast control must be provided for the user to enable him to obtain a display with optimum optical quality It is an object of the present invention to provide a dπver de\ ice that is optimized for obtaining a display with optimum optical quality without the need for adjustment by the user To achieve this, the dπver circuit is characteπzed in that the dπver circuit includes a means for stoπng a coπection factor to coπect the basic setting of the adjustable characteπstic of the dπver circuit and in that the dπver circuit is operative to adjust the adjustable characteπstic based on the basic setting and the coπection factor Dπver devices manufactured in a diffusion process can have tolerances as large as 20% The basic setting allows the manufacturer of the dπver device to coπect for the IC manufactuπng spread of the dπver circuit The manufacturer of the dπver device can store a basic setting in the device which represents a compromise setting on the basis of which the dπver device can generate a dπve signal that allows many display devices to operate within the optical range of the display device When a specific dπver device is combined with a specific display device to a display module, the basic settings of the dπver device can be sub-optimum for that specific display device This maybe caused by the manufactuπng spread of the display device or the differences between vaπous product lines The coπection factor can be used by the manufacturer of the display module to apply a general coπection factor which is based on a particular model of display devices, or the manufacturer of the display module can measure the optical quality of the display module and, by employing a calibration procedure, can determine a coπection factor to adjust the basic setting that was stored by the dπver device manufacturer The dπver device includes means for stoπng this coπection factor Because the dπver device uses both the stored basic setting and the stored correction factor to adjust its adjustable characteπstics, the manufacturer of the display module can optimize the optical quality of the associated display module Since the display quality can be optimized by the manufacturer of the display module, the user receives a display module that needs no further optimization As a consequence, the user no longer needs adjustment means in order to obtain a display with optimal optical quality The optical quality of the display device depends on several characteπstics of the dπve signal from the dπver device Important characteπstics are the amplitude of the dπve signal, frequency of the dπve signal and temperature dependence The dπver device can contain multiple means for stoπng a basic setting and multiple means for stoπng a coπection factor The basic setting and the coπection factor can be stored in a memory Each pair of basic setting and corresponding coπection factor is then used by the dπver circuit to adjust the characteπstic to which the settings coπespond The present invention will now be explained with reference to the drawing figures Fig 1 shows the dπver device according to the invention Fig 2 shows the display module according to the invention Fig 3 shows a display module according to the invention which includes temperature compensation means The explanation is based on an LCD display device, but the invention can also be applied to other display technologies The dπver device 1 according to Figure 2 can be used to generate the dπve signals for a display device The dπver device 1 includes a data processing unit 3 which receives data to be displayed via a data port 5 The data to be displayed, received via the data port 5, is then converted to data which is in a graphical format by the data processing unit 3 This data, which is in a graphical format, is then made available on an output 6 of the data processing unit 3 and is used by a waveform generation unit 7 to generate a dπve signal for a display device This dπve signal for the display device is made available on an output 9 of the waveform generation unit 7 For generating the dπve signal for the display device, the waveform generation unit 7 receives information about characteπstics of the dπve signal for the display device from a waveform parameter unit 11 via an output 13 The waveform parameter unit includes a memory 15 for stoπng a basic setting and a memory 19 for stoπng a correction factor The information about characteπstics of the dπve signal for the display device is generated by the waveform parameter unit 11 based on the basic setting stored in the memory 15 and the coπection factor stored in the memory 19 The memory 15 can be accessed via a first port 17 and the memory 19 can be accessed via a second port 21 Using an addressing scheme it is also possible to access both memoπes 15, 19 via a common port, or to access both memoπes 15, 19 via the data port 5, which is also used for transfeπng the data to be displayed to the dπver device 1 By stoπng a basic setting determined by calibrating the dπver device 1 in the memory 15, a characteπstic of the dπver device 1 can be altered resulting in an altered dπve signal on the output 9 of the waveform generation unit 7. The dπve signal for the display device on the output 9 can be adjusted to suit a typical display device The manufacturer of the dπver device 1 guarantee specifications related to the basic setting can in this way when the dπver device 1 is delivered to the customer. By stoπng a coπection factor in the memory 19, characteπstics of the dπver device 1 can be changed, away from the basic settings, resulting in a changed dπve signal on the output 9 of the waveform generation unit 7. By being able to change the characteπstics away from the basic setting, the characteπstics of the dπver device 1 can be adjusted to a particular model display devices or to a specific display device connected to the dπver device 1. The display module 30 according to Figure 2 includes both the dπver device 1 and a display device 25. Now that a specific dπver device is connected to a specific display device, it is possible to match the characteπstics of the dπver device 1 to the display device 25. The basic setting stored m the means 15 will yield an acceptable but sub-optimal optical quality of the display module. A manufacturer of the display module 30 can determine a correction factor and store the coπection factor in the means 19 which can be accessed via the second port 21. In this way it is possible to adjust the characteπstics of the dπver device 1, which result in a dπve signal on the output 9 of the waveform generation unit 7 which yields an optimal optical quality of the display module 30. The output 9 of the waveform generation unit 7 is connected to the input 23 of the display device 25. The dπver device 1 and the display device 25 will remain combined through the life of the display module 30 in which they are included, resulting a display module 30 which will yield optimal optical quality and requires no further adjustment means for a user. The display unit 30 according to Figure 3 includes the dπver circuit 1 with a temperature correction means 12 and the display device 25. The temperature coπection means 12 can be part of the waveform parameter unit 11 The temperature coπection means 12 receives temperature information of the environment in which the display module 30 is operated. The temperature coπection means 12 also receives parameters via the memory 15 and the memory 19. The waveform parameter unit 11 can supply a waveform parameter, via output 13, to the waveform generation unit, where the waveform parameter is determined based on the basic setting, the coπection factor, and the temperature information. Figure 4 illustrates the use of the basic setting, the coπection factor and the temperature information in order to obtain a waveform parameter The graph shows a possible relation between the basic setting, the coπection factor, the temperature information and the maximum level of the dπve signal The hoπzontal axis denotes the temperature information T env and the vertical axis denotes a waveform parameter, the maximum level of the dπve signal V max The manufacturer of the dπver circuit 1 determines a basic setting for the dπver circuit 1 which takes into account the spread in the manufactuπng process of the dπver circuit 1 and a typical temperature dependence of a typical display device This results in a relationship between the temperature information T env received by the dπver circuit 1 and the maximum level V ma χ as shown by the curve in Figure 4 which runs through a point SL1 This relationship can be optimized to suit a specific display device 25 to which the dπver circuit 1 is connected by stoπng a coπection factor SL2 in the means 19 for stoπng a coπection factor This results m a relationship between the temperature information T env received by the dπver circuit 1 and the maximum level V max , as shown by the curve in Figure 4 which runs through a point SL2 Since the display module 30 has an optimized temperature correction, the display module 30 will yield optimum optical quality over a large temperature range The user no longer needs further adjustment means to adjust for temperature changes The correction factor can be determined either based on a specific dπver circuit 1 and a specific display device 25 in a specific display module 30, or based on typical characteπstics of display devices in a certain product line, or display devices manufactured with a specific manufactuπng process, if the manufactuπng process has small tolerances Also multiple basic settings and coπection factors can be employed to provide more freedom to the manufacturer of display modules to optimize the optical quality In standard IC technology it is very difficult to obtain good accuracy for several parameters such as oscillator frequency, voltage levels and temperature dependence Therefore, the bias voltage generated by the dπver device 1 exhibits a large spread The dπver device 1 also contains an oscillator in the waveform generation unit 7, and the frequency of the oscillator is subject to manufactuπng process spread, supply and temperature vaπations The spread can be as large as a factor of 1 to 3 (-50% to +150% of the nominal frequency) The frame frequency inaccuracy will cause the flickeπng of the display under fluorescent light, if the frame frequency is equal to the mams frequency, or a multiple of it Tight tolerances are therefore required to prevent the frame frequency to be a multiple of 50 or 60 Hz The present invention allows the manufacturer of the dπver device and the manufacturer of the display module to reduce tolerances of the bias voltage and oscillator frequency in the same way as outlined for the temperature dependence.

Claims: CLAIMS 1. A dπver circuit (1) for a display device including a means (15) for stoπng a basic setting of an adjustable characteπstic of the dπver circuit (1), characteπzed in that the dπver circuit (1) includes a means (19) for stoπng a coπection factor to coπect the basic setting of the adjustable characteπstic of the dπver circuit (1) and in that the dπver circuit (1) is operative to adjust the adjustable characteπstic based on the base setting and the coπection factor 2. A dπver circuit as claimed in claim 1, characteπzed in that the means (19) for stoπng a coπection factor to coπect the basic setting of the adjustable dπver characteπstic is accessible 3. A dπver circuit as claimed in claim 1, or 2, characteπzed in that the means (15) for stoπng the basic setting of an adjustable dπver characteπstic is of the PROM type 4. A dπver circuit as claimed in claim 1,2,3, or 4, characteπzed in that the coπection factor which enables the dπver circuit (1) to coπect the basic setting of the adjustable characteπstic of the dπver circuit (1) has a substantially smaller adjustment range than the basic setting of the adjustable characteπstic of the dπver circuit (1). 5. A display module including the display dπver (1) as claimed in claim 1 or 2, and a display device (25) connected to the display dπver (1), characteπzed in that the coπection factor in the means (19) for stoπng a coπection factor is based on an individual property of the display device (25) 6 A method of adjusting an individual property of a display module (30) containing a display device (25) and a dπver circuit (1) connected to this display device (25), characteπzed in that the method includes the following steps determining a basic setting based on expected characteπstics of the display device (25) and characteπstics of the dπver circuit (1), stoπng the determined basic setting to be used by the dπver circuit (1), determining a correction factor to the basic setting based on the actual characteπstic of the display device (25) and the characteπstics of the dπver circuit (1) when the basic setting is used, stoπng the correction factor to be used by the dπver circuit (1)

Inventors: NEGOI ANDY C, SMITH ADAM J, NEGOI, ANDY, C., SMITH, ADAM, J.
Applicants: KONINKL PHILIPS ELECTRONICS NV, KONINKLIJKE PHILIPS ELECTRONICS N.V.
Application year: 2001
Main classification: G09G5
IPC codes: G02F1, G09G3, G09G5, H04N5, H04N17