JP3436081B2 - Adjustment method of D / A converter, data processing circuit, display device, electronic device, and liquid crystal projector - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a D / A converter adjusting method, a display device, and an electronic apparatus suitable for use in high-definition image display by a liquid crystal panel.

[0002]

2. Description of the Related Art A liquid crystal panel is used, for example, in a direct-view small monitor or a projection large monitor, and in either case, high definition is required in accordance with improvement in display capacity of personal computers and spread of high-definition. There is. Therefore, the operating frequency is inevitably increased, and it becomes difficult to secure a sufficient charging time for each liquid crystal cell. For this reason, there is known a technique for expanding a single-system digital image signal into an N-phase digital signal and ensuring a sufficient charging time for the liquid crystal cell. The number of phases N is about “6” in the SVGA mode (800 × 600 dots).

According to this technique, N D / A converters are provided corresponding to N-phase digital signals.
The liquid crystal cell is driven by the N-phase analog signal output from the / A converter. Where each D /
When the characteristics of the A converter vary, vertical stripe noise is generated on the screen, so the D / A converter is rotated (the D / A converter corresponding to the analog signal of each phase is appropriately switched to make the noise inconspicuous. ) Is common. Therefore, if the number of phases N is “6”, a switch of “6 inputs × 6 outputs = 36 contacts” is required. For these techniques, for example, Japanese Patent Laid-Open No. 8-22
No. 7065.

Furthermore, in recent years, XGA (1024 × 76
A display capability of about 8) is required. In order to obtain the operating frequency corresponding to this, it is necessary to increase the number of phases N to about "12". However, suppose that the D / A of the "12" phase
If you want to rotate the converter, select "12 x 12".
This requires a switch of “= 144 contacts”, which causes a problem that the circuit becomes large-scale. Furthermore, the phase number N is "1.
When it becomes about 2 ", there is a problem that rotation is likely to be conspicuous on the screen. Therefore, for XGA, it is common to eliminate the need for rotation by suppressing variations in the characteristics of the D / A converter as much as possible.

However, the D / A converter has various characteristics such as non-linearity, full-scale value and differential error.
In order to make all of these characteristics within the allowable range for the "12" phase D / A converter, extremely complicated adjustment work was required. For example, among the above characteristics, the “full scale value” refers to the output current value with respect to the maximum value of the digital signal, and the allowable range of the variation is about “± 0.1%”. As described above, the D / A converter of the high-definition liquid crystal panel is different from the circuit of general consumer equipment in that extremely high accuracy is required, and this adjustment work is required in order to popularize the high-definition liquid crystal panel. Simplification is essential.

A method of aligning the full scale values will be described here. A "current output type" is mainly used for the D / A converter for the liquid crystal panel. That is, the D / A converter becomes a constant current source that outputs a current according to the digital signal. When this output current is supplied to the load resistance, an output voltage equal to the product of the current and the resistance value is obtained. Then, finally, the liquid crystal cell is driven by the amplified voltage. Therefore, when the D / A converter has a variation in the full-scale value, the variation in the output voltage can be suppressed by increasing the resistance value of the load resistor connected to the D / A converter having a low full-scale value. .

[0007]

The present inventor has examined simplification of the adjustment work from the two aspects of "reexamining the adjustment method itself" and "reducing variations even before adjustment."

First, in the former case, it is possible to use a laser trimming resistor as a load resistor. The laser trimming resistor adjusts the resistance value by burning out a thin film or thick film rectangular resistor with a laser. This resistor may be formed by connecting a number of resistance elements in parallel. The adjustment of the resistance value is also to adjust the resistance value (composite resistance value) by burning off the resistance element with a laser as required. The laser trimming resistor is advantageous in that it has a simple structure and is inexpensive, and the adjustment can be automated, but it has a drawback that it cannot be adjusted in the direction of decreasing the resistance value. Therefore, it is necessary to consider that this defect does not hinder the adjustment work.

Next, regarding the latter, as described above, the D / A converter has various characteristics such as non-linearity, full-scale value, and differential error. The present inventor has predicted that the variation in these characteristics is caused by the manufacturing process of the integrated circuit having the D / A converter. Therefore, it seems that variations in characteristics can be suppressed by forming all required D / A converters on the same chip.

Therefore, an integrated circuit in which “2 rows × 6 columns = 12” D / A converters were actually formed on one chip was prepared. In this integrated circuit, the power supply line is extended to almost the central portion of "2 rows × 6 columns", and the integrated circuit is branched from this to suppress variation due to internal resistance of the power supply line. When the characteristics of the D / A converter manufactured in this manner were measured, it was confirmed that variations such as non-linearity and differential error could be suppressed to a satisfactory level.

However, it has been found that the variation of the full scale value exceeds the allowable range (± 0.1%). As the analysis progressed further, the full-scale values of the D / A converter in the central part of each "row" of "2 rows x 6 columns" were almost the same, whereas the closer to both ends of each "row", The full scale value tended to be smaller.

The present inventor believes that the reason why the above tendency occurs is due to the package stress caused by aging, that is, temperature change. This was discovered by an accelerated test (temperature cycle test) for considering the deterioration of the product due to aging. That is, when the integrated circuit is subjected to a temperature cycle test,
Since stress is applied to the chip by thermal expansion and contraction, the lead wire such as aluminum foil formed on the integrated circuit is deformed. Here, since this stress becomes stronger in the peripheral portion of the integrated circuit, the deformation of the lead wire becomes larger in the peripheral portion of the integrated circuit. Further, the longer the branch line of the power supply line, the greater the change in resistance value due to deformation. Therefore, it is considered that due to the synergistic effects of these causes, the internal resistance of the D / A converter becomes higher toward the peripheral portion, and as a result, the output current value decreases.

The present invention has been made in view of the above-described examination result, and provides a D / A converter adjusting method, a display device, and an electronic apparatus which can make the characteristics of the D / A converter uniform by simple adjustment. Is intended.

[0014]

A D / A converter adjusting method of the present invention is a D / A converter adjusting method for adjusting output voltages of a plurality of D / A converters arranged in a predetermined direction, A differential amplifier circuit that supplies the first D / A converter with a digital signal whose first output voltage, which is the maximum output voltage of the first D / A converter among the plurality of D / A converters, is supplied to the first D / A converter. The first input to each of the two input ends of
Input voltage and the reference output voltage of a reference D / A converter sandwiched between two D / A converters of the plurality of D / A converters are input, and the first output voltage and the reference output voltage are input. The resistance value of the resistor to which the output current of the first D / A converter is supplied is adjusted so that the difference between and is within a predetermined allowable range.

In the above D / A converter adjusting method, a laser trimming resistor may be used as the resistor.

In the above D / A converter adjusting method, a semi-fixed resistor or a variable resistor may be used as the resistor.

In the above D / A converter adjusting method, the resistance value of the resistor may be set using a digital potentiometer.

The data processing circuit of the present invention is a data processing circuit in which a plurality of D / A converters are arranged on a single chip along a predetermined direction, and is the first of the plurality of D / A converters. The D / A converter includes a first resistor to which an output current is supplied, and the resistance value of the first resistor is equal to that of the first D / A converter at each of two input ends of a differential amplifier circuit. The first output voltage, which is the maximum output voltage, and the reference output voltage of the reference D / A converter sandwiched between two D / A converters of the plurality of D / A converters are input, The difference between the first output voltage and the reference output voltage is adjusted to fall within a predetermined allowable range.

In the above data processing circuit, the first
The output voltage of the D / A converter may be input to an operational amplifier and amplified by an amplifier including the operational amplifier and the second resistor.

The display device of the present invention is characterized by including the above-mentioned data processing circuit.

The electronic equipment of the present invention is characterized by including the above display device.

The liquid crystal projector of the present invention is characterized by including the above-mentioned data processing circuit.

[0023]

DETAILED DESCRIPTION OF THE INVENTION

1. First Embodiment Next, a configuration of a liquid crystal display device according to a first embodiment of the present invention will be described with reference to FIG. The liquid crystal display device is used as a light valve of an electronic device such as a liquid crystal projector, and includes a liquid crystal panel 10 and a scanning side drive circuit 20.
And a data processing block 30. The liquid crystal panel 10 is composed of a plurality of lines of liquid crystal cells, and the scanning side drive circuit 20 makes the liquid crystal cells chargeable for each line. Then, the data processing block 30 supplies data (voltage) corresponding to each liquid crystal cell based on the image data D.

Inside the data processing block 30, the gamma correction circuit 31 compensates the gradation characteristic of the image data D and outputs the compensated image data D '. Polyphase expansion circuit 32
Is composed of a shift register 33 and a latch circuit 34, and converts the compensation image data D ′ into multi-phase (12-phase) data D1 to
Expand to D12. The polarity reversing circuit 35 is used for the liquid crystal panel 10.
The multi-phase data D for each dot
Invert the polarity of 1 to D12. The polarity here means the direction of the electric field finally applied to the liquid crystal cell, and reversing the polarity of the signal or data means that the direction of the electric field applied to the liquid crystal cell is reversed. Is to change.

Next, the D / A converters 101 to 112.
Converts the polarity-inverted multiphase data D1 to D12 into analog signals (current signals). Amplifier circuits 201 to 212
Outputs these current signals after converting them into voltage signals and amplifying them. Then, in the liquid crystal panel 10, the multiphase data D1 to D12 are supplied to the liquid crystal cells in the line selected by the scanning side drive circuit 20, and each liquid crystal cell is driven.

Here, the D / A converters 101 to 112 are provided.
2 and the details of the amplifier circuits 201 to 212 will be described with reference to FIG. In the figure, the integrated circuit chip 100 has a D
/ A converters 101 to 112 are arranged in “2 rows × 6 columns”. Inside the amplifier circuit 201, 201a is a laser trimming resistor, and the D / A converter 10
When the output current I1 of 1 is supplied to the laser trimming resistor 201a, an output voltage V1 equal to the product of the resistance value and the output current I1 appears.

The operational amplifier 201d and the resistor 201 are also provided.
An amplifier is formed by b and 201c, and the output voltage V1 is amplified and output. This amplified voltage V1
Is supplied to the liquid crystal panel 10 as the data D1. 201e is a voltage measuring terminal, which is provided to measure the output voltage V1 during laser trimming. The other amplifier circuits 202 to 212 are also configured similarly to the amplifier circuit 201.

Next, FIG. 3 shows a configuration of an adjusting circuit for adjusting the laser trimming resistors 201a to 212a provided in each of the amplifier circuits 201 to 212. 3 in the figure
Reference numeral 01 is a difference amplifier, which amplifies the difference between the voltages input to its two input terminals with a predetermined gain and outputs it. 302
Is a laser trimming device, which performs laser trimming on the laser trimming resistors 201a to 212a to be trimmed.

Next, a method of performing laser trimming using this circuit will be described.

First, each D / A converter 101-112.
, The digital signal whose D / A converter output has the maximum value (full scale value) is supplied. As a result, each D
/ A converter to full-scale output current I1 to I12
Is output. The output currents I1 to I12 should ideally be the same, but in reality, as described above, the chip 1
The closer the D / A converter is to the periphery of 00, the output current I1
~ I12 becomes low.

Next, one of the D / A converters 101 to 112 is defined as a reference D / A converter. A preferred standard D / A converter is a D / A converter other than the two ends, which has little secular change with temperature change.
D / A of A converters 102 to 105 and 108 to 111
The D / A converters 103, 104, 109, 110 located in the central portion are more preferable.

"D / A converter other than both ends" is, in other words, "D / A converter sandwiched between two other D / A converters".
It can be expressed as “A converter”, and “the D / A converter located in the central portion” means “the k / 2th or (K + 1) / 2th D / A of the k D / A converters from the end. It can be expressed as “A converter”. Where k
Is the number of D / A converters arranged in one row, and is “6” in the example of FIG.

Next, the input terminal 301a of the differential amplifier 301
And an amplifier circuit 204 connected to the reference D / A converter.
Of the amplifier circuit 201 is connected to the input terminal 301b. Then, based on the difference between the voltages appearing at the voltage measuring terminals 201e and 204e, that is, the difference between the output voltages of the D / A converters 101 and 104, the laser trimming resistor 201a is controlled so that this difference falls within a predetermined allowable range. Laser trimming will be performed.

Similarly, the other D / A converters 10 will be described below.
2, 103, 105 to 112, the output voltage is measured, the measured voltage is compared with the output voltage of the reference D / A converter 104, and each D is adjusted so that the difference between them is within a predetermined allowable range. The laser trimming resistor 201a corresponding to the / A converter is laser-trimmed.

As described above, in the present embodiment, since the other D / A converters are adjusted with the D / A converter, which is relatively less affected by the package stress caused by the temperature change, as a reference, the characteristics of the D / A converters are adjusted. Can be aligned with high precision. Moreover, the D / A converter that is easily affected by the package stress caused by the temperature change is
Since the resistance value of the laser trimming resistor can be adjusted to increase the output voltage (direction to burn out the resistance element) in order to increase the output voltage, efficient adjustment work can be performed while fully utilizing the features of the laser trimming resistor. be able to. If the resistance value of the laser trimming resistor before trimming is made lower than the actually required resistance value, a desired resistance value can be obtained by trimming.

2. Second Embodiment Next, an example in which the liquid crystal display device of the first embodiment is applied to a liquid crystal projector will be described with reference to FIG.

In the figure, a light source lamp unit 1102 is provided inside a liquid crystal projector 1100.
The projection light emitted from the lamp unit 1102 is reflected by the plurality of mirrors 1106, 1106 in the light guide 1104.
... and two dichroic mirrors 1108 separate the RGB into three primary colors, and the light is emitted to the three liquid crystal display devices 1110R, 1110G, and 1110B associated with the respective primary colors.

The configurations of the liquid crystal display devices 1110R, 1110G and 1110B are as described in the first embodiment. The light modulated by these liquid crystal display devices enters the dichroic prism 1112 from three directions. In the dichroic prism 1112, red (R) and blue (B) lights are bent by “90 °”, and green (G) lights go straight. Therefore, the images of the respective colors are combined, and the color image is projected on the screen or the like via the projection lens 1114.

3. Third Embodiment Next, an example in which the liquid crystal display device of the first embodiment is applied to a personal computer will be described with reference to FIG.

In the figure, a personal computer 120
0 is a main body 1204 equipped with a keyboard 1202,
It is composed of a liquid crystal display 1206. The liquid crystal display 1206 is configured by adding a color filter and a backlight to the liquid crystal display device of the first embodiment.

4. Modifications The present invention is not limited to the above-mentioned embodiment,
For example, various modifications are possible as follows.

(1) In the second and third embodiments, the liquid crystal projector 1100 and the personal computer 1200 are mentioned as examples of the electronic device, but the liquid crystal panel may be applied to various electronic devices other than these. Needless to say. Furthermore, the present invention can be applied to various devices that use a plurality of D / A converters, even electronic devices that do not use a liquid crystal display device.

(2) In the first embodiment, one gamma correction circuit 31 is provided in the preceding stage of the polyphase expansion circuit 32. However, instead of the gamma correction circuit 31, the polyphase expansion circuit 32 and the polarity inversion circuit. An independent gamma correction circuit may be provided for each of the phases with respect to 35. According to this configuration, the gamma correction characteristics of each phase are adjusted to suppress variations in full-scale value and laser trimming can be omitted. However, since the gamma correction circuit requires a relatively large circuit area, there is a drawback that the circuit becomes large as a whole.

(3) In the first embodiment, the laser trimming resistor 2 is used to adjust the full scale value.
Although 01a to 212a are used, various semi-fixed resistors and variable resistors such as potentiometers may be used instead.

An example of this potentiometer is shown in FIG.
FIG. 6 shows an example of a digital potentiometer, and digital data (DATA) is first input to the decoder 601. The decoder 601 has a built-in non-volatile memory such as a flash memory, and can hold DATA once input inside. This DATA is decoded inside the decoder 601, and the switch control signal (SW
Only one of 1 to SW5 is High (Active), and the rest is L
ow (Non Active) Here, analog switch 6
02 connected resistors 603 to 608
The resistance value from the input (INPUT) to the analog ground of the resistor 608 can be varied.

This digital potentiometer does not require a circuit scale as large as that of the gamma correction circuit, and the resistance value can be easily changed by the digital input. In addition, it is impossible to change the resistance value once it is adjusted with the laser trimming resistor and installed in the device, but with this digital potentiometer, D
Even if the characteristics of the / A converter change, the resistance value can be easily changed by inputting DATA in the device installation state.

[0047]

[0048]

[0049]

[0050]

[0051]

As described above, according to the present invention,
A plurality of D / A's formed along a predetermined direction on one chip
One of the converters sandwiched between the other two D / A converters is used as the reference D / A converter, and the characteristics of the other D / A converters are adjusted based on the characteristics of the reference D / A converter. The characteristics of the D / A converter can be made uniform by simple adjustment.

By using a laser trimming resistor to adjust the characteristics (full scale value) of this D / A converter, it is possible to make extremely industrial adjustment, and there is an advantage that mass production is possible.

In addition, by using a digital potentiometer to adjust the characteristics (full scale value) of the D / A converter, the characteristics of the D / A converter can be changed due to secular changes after assembling equipment such as a liquid crystal projector. Even if it changes, there is an advantage that it can be readjusted.

Further, by adjusting the current value of the reference current source in order to adjust the characteristics (full scale value) of the D / A converter, the current value of the reference current source is higher than that of the D / A converter output. Since it is small, the resistor used for the adjustment can be made small, so that it can be built in one IC and can be made into one package, so that there is an advantage that the environment resistance can be made inexpensive and strong.

[Brief description of drawings]

FIG. 1 is a block diagram of a liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a main part of the liquid crystal display device.

FIG. 3 is a block diagram of an adjusting circuit of the liquid crystal display device.

FIG. 4 is a plan view of a liquid crystal projector 1100 according to a second embodiment.

FIG. 5 is a personal computer 12 of a third embodiment.
It is a front view of 00.

FIG. 6 is an explanatory diagram of a digital potentiometer.

FIG. 7 is a diagram illustrating that a reference current source is provided in each D / A converter.

[Explanation of symbols]

10 LCD panel 20 Scanning side drive circuit 30 data processing blocks 31 Gamma correction circuit 32 Polyphase expansion circuit 33 shift register 34 Latch circuit 100 chips 101-112 D / A converter 201-212 amplifier circuit 201a-212a Laser trimming resistor 201b, 201c resistors 201d operational amplifier 201e Voltage measurement terminal 204 amplifier circuit 204e Voltage measurement terminal 301 Differential amplifier 301a input end 301b Input end 302 Laser trimming device 601 decoder 602 analog switch 603 to 608 resistors 701 to 712 current source

Continuation of the front page (56) Reference JP-A-5-191287 (JP, A) JP-A-3-88427 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H03M 1 / 00-1/88

Claims (9)

(57) [Claims] 1. A D / A converter adjusting method for adjusting an output voltage of a plurality of D / A converters arranged in a predetermined direction, the first D / A converter among the plurality of D / A converters. A digital signal whose output is the maximum output voltage, which is the first output voltage, is supplied to the first D / A converter, and the first output voltage and the digital signal are supplied to each of the two input terminals of the differential amplifier circuit. A reference output voltage of a reference D / A converter arranged between two D / A converters of a plurality of D / A converters is input, and a difference between the first output voltage and the reference output voltage is predetermined. Adjusting the resistance value of the resistor to which the output current of the first D / A converter is supplied so as to be within the allowable range of. 2. The method for adjusting a D / A converter according to claim 1, wherein a laser trimming resistor is used as the resistor. 3. The method of adjusting a D / A converter according to claim 1, wherein a semi-fixed resistor or a variable resistor is used as the resistor. 4. The D / A converter adjusting method according to claim 1, wherein the resistance value of the resistor is set by using a digital potentiometer. How to adjust the converter. 5. A data processing circuit in which a plurality of D / A converters are arranged on a single chip along a predetermined direction, wherein a first D / A converter of the plurality of D / A converters outputs A first resistor supplied with a current, wherein the resistance value of the first resistor is:
A first output voltage, which is the maximum output voltage of the A / A converter, and a reference output voltage of a reference D / A converter sandwiched between two D / A converters of the plurality of D / A converters. A data processing circuit, wherein the data processing circuit is input and adjusted so that a difference between the first output voltage and the reference output voltage is within a predetermined allowable range. 6. The data processing circuit according to claim 5, wherein the output voltage of the first D / A converter is input to an operational amplifier and amplified by an amplifier including the operational amplifier and a second resistor. A data processing circuit characterized by: 7. A display device provided with the data processing circuit according to claim 5. 8. An electronic device comprising the display device according to claim 7. 9. A liquid crystal projector comprising the data processing circuit according to claim 5.