JP2002072969A - Liquid crystal drive circuit and liquid crystal display device - Google Patents

Abstract

(57) [Problem] To reduce a decrease in brightness of a liquid crystal panel and a decrease in driving capability of a liquid crystal output amplifier. SOLUTION: Due to the nature of the liquid crystal panel, the reaction speed of the liquid crystal panel is lowered and the brightness is lowered by lowering the temperature, but the liquid crystal level reference voltage generating circuit (11).
Has a negative temperature characteristic, so that when the temperature is low, the reference voltage for the liquid crystal level is increased, thereby compensating for a decrease in the reaction speed of the liquid crystal panel, thereby stabilizing the liquid crystal brightness. As the temperature rises, the liquid crystal output amplifier (131
To 134), the driving capability of the liquid crystal output amplifier itself is reduced. However, since the liquid crystal output amplifier reference voltage generating circuit 12 has a positive temperature characteristic,
The bias current of the liquid crystal output amplifier is stabilized, and the driving capability of the amplifier is prevented from lowering.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal driving technique, particularly to a technique for improving the image quality of a liquid crystal panel, and more particularly to a technique effective when applied to a small liquid crystal control LSI.

[0002]

2. Description of the Related Art A liquid crystal display device, which is an example of a display device, includes a liquid crystal panel (LCD) and a liquid crystal controller LSI for driving the liquid crystal panel. The liquid crystal controller LSI includes a power supply circuit for supplying a voltage used for driving the liquid crystal panel, a liquid crystal driver for driving the liquid crystal panel based on an output voltage of the power supply circuit, and a liquid crystal driver and a power supply circuit. It comprises a controller for controlling the operation. The power supply circuit includes a reference voltage generation circuit for generating a reference voltage, and a liquid crystal output amplifier for forming a voltage used for driving a liquid crystal panel based on an output voltage of the reference voltage generation circuit. Become.

As an example of a document describing a liquid crystal display device, see “Electronic Communication Handbook (No. 473)” issued by Ohm Co., Ltd. on August 20, 1983.
Page)].

[0004]

SUMMARY OF THE INVENTION Liquid Crystal Control LS
I is formed on one semiconductor substrate such as a single crystal silicon substrate. The inventors of the present application have examined such a liquid crystal controller LSI, and found that the image quality of the liquid crystal panel deteriorates in relation to the temperature characteristics of the liquid crystal panel.

[0005] That is, when the liquid crystal panel is driven in a state where there is no voltage change, the reaction temperature of the liquid crystal panel is reduced due to a decrease in temperature, and the brightness is also reduced.

On the other hand, in a power supply circuit for outputting a voltage for driving a liquid crystal panel, the higher the temperature, the lower the performance of the liquid crystal output amplifier tends to be. This is because the rise in temperature reduces the bias current in the liquid crystal output amplifier, and reduces the drive capability of the liquid crystal output amplifier itself. The lowering of the liquid crystal output amplifier driving ability lowers the rising and falling of the liquid crystal output voltage, thereby lowering the image quality of the liquid crystal panel.

As described above, the brightness of the liquid crystal panel and the driving capability of the liquid crystal output amplifier are in a trade-off relationship as long as a power supply circuit having a constant temperature characteristic is used, so that it is difficult to improve both characteristics. .

An object of the present invention is to provide a technique for simultaneously reducing a decrease in brightness of a liquid crystal panel and a decrease in driving capability of a liquid crystal output amplifier.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0010]

The following is a brief description of an outline of a typical invention among the inventions disclosed in the present application.

That is, a power supply circuit capable of outputting a voltage used for driving a liquid crystal panel and a liquid crystal driver for driving the liquid crystal panel by supplying an output voltage of the power supply circuit to the liquid crystal panel are included. When a liquid crystal drive circuit is configured with a first reference voltage generation circuit having a negative temperature characteristic and generating a liquid crystal level reference voltage,
An output amplifier for forming a voltage used for driving the liquid crystal panel based on an output voltage of the first reference voltage generation circuit; and a bias voltage having a positive temperature characteristic and supplied to the output amplifier. And the second reference voltage generating circuit.

According to the above means, the first reference voltage generating circuit has a negative temperature characteristic. Due to the nature of the liquid crystal panel, the reaction speed of the liquid crystal panel decreases as the temperature decreases,
Although the brightness also decreases, since the first reference voltage generating circuit has a negative temperature characteristic as described above, when the temperature is low, the reference voltage for the liquid crystal level increases, and the reaction speed of the liquid crystal panel decreases. Thus, the brightness of the liquid crystal is stabilized.

Further, the second reference voltage generating circuit has a positive temperature characteristic. As the temperature rises, the bias current in the liquid crystal output amplifier decreases, and the driving capability of the liquid crystal output amplifier itself decreases. However, since the second reference voltage generation circuit has a positive temperature characteristic as described above, The bias current of the output amplifier is stabilized, and the reduction in the driving capability of the amplifier is reduced.

At this time, the first reference voltage generation circuit and the second reference voltage generation circuit correspond to a predetermined current mirror ratio based on a depletion type transistor and a current flowing through the depletion type transistor. A current mirror circuit for obtaining a current and a transistor for converting an output current of the current mirror circuit into a voltage can be provided.

In order to easily realize the negative temperature characteristic of the first reference voltage generation circuit and the positive temperature characteristic of the second reference voltage generation circuit, the current mirror circuit included in the first reference voltage generation circuit is used. And the current mirror ratio of the current mirror circuit included in the second reference voltage generating circuit may be adjusted.

Further, the current mirror circuit may include a switch capable of changing a current mirror ratio.

[0017]

FIG. 2 shows a configuration example of a liquid crystal display device according to the present invention.

The liquid crystal display device 20 shown in FIG. 2 is not particularly limited, but is mounted on a portable information terminal.
It comprises a liquid crystal display panel 21 and a small liquid crystal controller LSI 22 for driving it. Although not particularly limited, the small liquid crystal controller LSI 22 includes a power supply circuit 222 for supplying a voltage used for driving the liquid crystal panel 21 and a drive circuit for driving the liquid crystal panel 21 based on an output voltage of the power supply circuit 222. Liquid crystal driver 221 and the liquid crystal driver 221 and power supply circuit 222
And a controller 223 for controlling the operation of
For example, it is formed on one semiconductor substrate such as a single crystal silicon substrate by a known semiconductor integrated circuit manufacturing technique. The liquid crystal panel 21 has a plurality of liquid crystal elements arranged in a grid pattern, and enables image display based on the output of the liquid crystal driver 221.

FIG. 1 shows a configuration example of the power supply circuit 222.

As shown in FIG. 1, the power supply circuit 22
Reference numeral 2 denotes a liquid crystal level reference voltage generation circuit (first reference voltage generation circuit) for generating a liquid crystal level reference voltage.
A boosting amplifier 131 for boosting the output voltage of the liquid crystal level reference voltage generating circuit; a variable resistor VR1 for adjusting the gain of the boosting amplifier 131; and a resistor R1 connected in series to the variable resistor VR1. A variable resistor VR2 for enabling contrast adjustment of the panel 21, and ladder resistors R2, R3, R4 for dividing a voltage taken in through the variable resistor VR2 into a plurality of voltages having different levels. R6 and the ladder resistors R2 and R
3, liquid crystal output amplifiers 131, 132, 133, and 134 for forming voltages used for driving the liquid crystal panel 21 based on the divided output voltages of R3, R4, and R6. And a reference voltage generating circuit (second reference voltage generating circuit) 12 for a liquid crystal output amplifier for generating a bias voltage Vb supplied to 133 and 134.

The liquid crystal level reference voltage Vref output from the liquid crystal level reference voltage generation circuit 11 is transmitted to the non-inverting input terminal (+) of the liquid crystal level boosting amplifier 121. A variable resistor VR1 is connected between the output terminal of the liquid crystal level boosting amplifier 121 and the inverting input terminal (-). The variable resistor VR1 is a liquid crystal level boosting amplifier 12
1 can be adjusted, and the variable resistor VR1
Liquid crystal level boosting amplifier 1 according to the relationship between
A gain of 21 is determined. LCD Level Boost Amplifier 1
21 is a variable resistor VR2 for contrast adjustment.
Are applied to the voltage dividing resistors R2 to R6. Voltage dividing resistor R
The output voltage from the series connection node of R2 and R3 is transmitted to the non-inverting input terminal of the liquid crystal output amplifier 131. Voltage dividing resistor R
The output voltage from the series connection node of R3 and R4 is transmitted to the non-inverting input terminal of the liquid crystal output amplifier 132. Voltage dividing resistor R
The output voltage from the series connection node of R4 and R5 is transmitted to the non-inverting input terminal of the liquid crystal output amplifier 133. Voltage dividing resistor R
The output voltage from the series connection node of R5 and R6 is transmitted to the non-inverting input terminal of the liquid crystal output amplifier 134. The liquid crystal output amplifiers 131 to 134 are voltage followers whose output terminals and inverting input terminals are coupled.

Here, the liquid crystal level reference voltage generating circuit 11 has a negative temperature characteristic, and the liquid crystal output amplifier reference voltage generating circuit 12 has a positive temperature characteristic. The negative temperature characteristic and the positive temperature characteristic are not particularly limited, but can be realized by adjusting the current mirror ratio of the current mirror circuit.

FIG. 3 shows a configuration example of the liquid crystal driver 22.

As shown in FIG. 3, the liquid crystal driver 22 includes a plurality of driving circuits 31-1, 31-2,.
1-X (X is a positive integer). Since the plurality of drive circuits 31-1, 31-2,..., 31-X have the same configuration, only the drive circuit 31-1 will be described in detail here.

The drive circuit 31-1 is an n-channel type MO
S transistors Q11, Q12 and p-channel type M
OS transistors Q13 and Q14 are included. The gate electrodes of the MOS transistors Q11 to Q14 have corresponding liquid crystal level selection signals IN11, IN12, IN respectively.
13, IN14 are transmitted. Liquid crystal level selection signals IN11, IN12, IN13, IN14
Is a signal output from the controller 223 shown in FIG. 2 in accordance with the display data.
The corresponding liquid crystal level is selectively supplied to the liquid crystal panel 21. For example, when the liquid crystal level selection signal IN11 is asserted to a high level, the n-channel MOS transistor Q11 is turned on, and the liquid crystal level V1 is selectively supplied to the liquid crystal panel 21. Liquid crystal level selection signal IN1
2 is asserted to a high level, the n-channel MOS transistor Q12 is turned on and the liquid crystal level V2 is turned on.
Is selectively supplied to the liquid crystal panel 21. When the liquid crystal level selection signal IN13 is asserted low, p
The channel type MOS transistor Q13 is turned on, and the liquid crystal level V3 is selectively supplied to the liquid crystal panel 21.
When the liquid crystal level selection signal IN14 is asserted to a low level, the p-channel MOS transistor Q14 is turned on, and the liquid crystal level V4 is selectively supplied to the liquid crystal panel 21.

FIG. 4 shows a reference voltage generating circuit 1 for a liquid crystal level.
1 is shown.

An n-channel type MOS transistor Q4
5, Q46 are connected in series, and a p-channel type MO
S transistor Q41 is connected in series. 50 p-channel MOS transistors Q42-1 to Q42-5
The current mirror circuit 40 is formed by 0 being current mirror-coupled to the p-channel MOS transistor Q41. p-channel type MOS transistor Q
41 and the gate sizes of Q42-1 to Q42-50 are made equal to each other, and the current mirror ratio (this is indicated by M).
Is set to 1/50. In addition, the above-mentioned p-channel type MOS
A p-channel MOS transistor Q43 is connected in series to the transistors Q42-1 to Q42-50, and a gate electrode of the p-channel MOS transistor Q43 is supplied with a voltage of a series connection node of the MOS transistors Q41 and Q45. The bias voltage Vr
The power supply voltage dependence of ef is reduced. An n-channel MOS transistor Q44 for current-voltage conversion is connected in series to the p-channel MOS transistor Q43. p-channel type MOS transistor Q4
The reference voltage Vref for the liquid crystal level is obtained from a series connection node of the third transistor 3 and the n-channel MOS transistor Q44. The liquid crystal level reference voltage Vref is transmitted to the liquid crystal level boosting amplifier 121 as shown in FIG.

In FIG. 4, an n-channel MOS
Only the transistors Q45 and Q46 are of the depletion type, and the others are of the enhancement type.

FIG. 5 shows a configuration example of the reference voltage generating circuit 12 for the liquid crystal output amplifier.

An n-channel MOS transistor Q5
5, Q56 are connected in series, and a p-channel type MO
S transistor Q51 is connected in series. The p-channel MOS transistor Q52 is connected to the p-channel MO
A current mirror circuit 50 is formed by current mirror coupling to S transistor Q51. The gate sizes of the p-channel MOS transistors Q51 and Q52 are made equal to each other, and the current mirror ratio (shown by M) due to the current mirror coupling is set to 1/1. Further, the p-channel MOS transistor Q5
2, a p-channel MOS transistor Q53 is connected in series, and MOS transistors Q51, Q51 are connected to the gate electrode of the p-channel MOS transistor Q53.
By supplying the voltage of 55 series connection nodes,
The power supply voltage dependency of the liquid crystal level reference voltage Vref is reduced. p-channel type MOS transistor Q53
Is connected in series with an n-channel MOS transistor Q54 for current-voltage conversion. p-channel type M
A liquid crystal output amplifier bias voltage Vb is obtained from a series connection node of the OS transistor Q53 and the n-channel MOS transistor Q54. The liquid crystal output amplifier bias voltage Vb is transmitted to the liquid crystal output amplifiers 131 to 134 as shown in FIG.

In FIG. 5, an n-channel MOS
Only the transistors Q55 and Q56 are of the depletion type, and the others are of the enhancement type.

Here, the operation principle of the liquid crystal level reference voltage generation circuit 11 shown in FIG. 4 will be described.

The output voltage Vref of the liquid crystal level reference voltage generation circuit 11 is expressed by the following equation.

[0034]

(Equation 1)

In equation (1), Vthne is the threshold value of the enhancement type n-channel MOS transistor, βne is the transconductance of the enhancement type n-channel MOS transistor, M is the current mirror ratio, and Vthnd is the depletion type n-channel MOS transistor. Threshold value of the type MOS transistor, βnd
Is the transconductance of the depletion type n-channel MOS transistor. Here, the transconductance β is expressed by an enhancement type n-channel MOS transistor and a depletion type n-channel MOS
It is determined by the gate size of the transistor. Note that μ
Is the mobility, Cox is the gate capacitance, W is the gate width, and L is the gate length.

[0036]

(Equation 2)

[0037]

(Equation 3)

The liquid crystal level reference voltage generating circuit 1
The temperature characteristic of No. 1 is expressed by the following equation.

[0039]

(Equation 4)

Actually, both βnd and βne have a predetermined temperature characteristic, but when (βnd / βne) is set, it is a sufficiently small value with respect to equation (4). From Equation 4, the temperature characteristic of the liquid crystal level reference voltage generating circuit 11 can be adjusted by changing the current mirror ratio M which is a coefficient relating to the temperature characteristic of Vthnd.

The same applies to the liquid crystal output reference voltage generating circuit 12 shown in FIG. 5, and the temperature characteristic of the liquid crystal output reference voltage generating circuit 12 is a current mirror ratio which is a coefficient related to the temperature characteristic of Vthnd. By adjusting M, adjustment becomes possible.

FIG. 6 shows the temperature characteristics of the reference voltage generating circuit as shown in FIGS.

As is apparent from FIG. 6, the temperature characteristics of the current mirror circuit vary depending on the current mirror ratio (M). For example, as shown in FIG.
50 p-channel MOS transistors Q42-1 through Q42 are added to p-channel MOS transistor Q41.
When the current mirror ratio becomes M = 1/50 by the current mirror coupling of −50, a negative temperature characteristic is realized. Also, as shown in FIG. 5, when the p-channel MOS transistor Q51 is current-mirror-coupled to the p-channel MOS transistor Q51, the current mirror ratio becomes positive when M = 1/1. Temperature characteristics can be obtained.

FIG. 7 shows a configuration example of the liquid crystal output amplifier 131.

N-channel type MOS transistor Q7
2 and Q73 are differentially coupled by their source electrodes being coupled to ground GND via an n-channel MOS transistor Q71. The n-channel MOS transistor Q71 functions as a constant current source when a predetermined bias voltage Vb is supplied to the gate electrode. The bias voltage Vb is supplied by the liquid crystal output amplifier reference voltage generation circuit 12. In addition, the n-channel type M
The drain electrodes of the OS transistors Q72 and Q73 are connected to the corresponding p-channel type MOS transistor Q7.
4, Q75 to the high potential side power supply Vdd.
The p-channel MOS transistor Q74 is mirror-coupled to the p-channel MOS transistor Q75. A non-inverting input terminal (+) is extracted from the gate electrode of the n-channel MOS transistor Q72, and an inverting input terminal (-) is extracted from the gate electrode of the n-channel MOS transistor Q73. p-channel type MOS
An output of a differential pair is obtained from a series connection node of the transistor Q74 and the n-channel MOS transistor Q72.
It is transmitted to the gate electrode of 76. p-channel type MOS
The source electrode of transistor 76 is coupled to high potential side power supply Vdd. p-channel type MOS transistor Q76
Is coupled to ground GND via an n-channel MOS transistor Q77. The n-channel MOS transistor Q77 functions as a constant current source when a predetermined bias voltage Vb is supplied to the gate electrode. p-channel type MOS transistor Q
An output voltage V1 of the liquid crystal output amplifier 131 is obtained from a series connection node of the MOS transistor 76 and the n-channel MOS transistor Q77. Further, a p-channel MOS transistor Q76 and an n-channel MOS transistor Q7
7, a capacitor C1 for stabilizing the level of the output voltage V1 is provided.

The other liquid crystal output amplifiers 132 to 134 have the same configuration as the liquid crystal output amplifier 131.

FIG. 9 shows the power supply circuit 222 shown in FIG.
The circuit to be compared is shown.

The power supply circuit 90 shown in FIG. 9 is greatly different from the power supply circuit 222 shown in FIG. 1 in that the liquid crystal level reference voltage Vref and the bias voltage Vb are formed by a common reference voltage generation circuit 91. It is a point. The temperature characteristic of the reference voltage generating circuit 91 is almost constant (0% /
° C).

As shown in FIG. 10, the liquid crystal panel 21 has such characteristics that the lower the temperature is, the lower the brightness of the liquid crystal is. In other words, even if the liquid crystal panel 21 is driven with the same voltage, the reaction speed of the liquid crystal panel 21 is reduced due to a decrease in temperature, thereby lowering the brightness of the liquid crystal.

The liquid crystal output amplifiers 131 to 134 are
As shown in FIG. 11, as the temperature rises, the driving capability of the liquid crystal output amplifier decreases. This is because the rise in temperature decreases the bias current used in the liquid crystal output amplifier, thereby lowering the drive capability of the amplifier itself. A decrease in the driving capability of the liquid crystal output amplifier slows down the rise and fall of the liquid crystal output voltage and also slows down the response to noise, resulting in deterioration of the image quality of the liquid crystal panel.

For example, if the reference voltage generating circuit 91 has a negative temperature characteristic, the reference voltage for the liquid crystal level increases when the temperature is low, thereby compensating for a decrease in the reaction speed of the liquid crystal panel and keeping the liquid crystal brightness constant. However, this is not preferable because when the temperature is low, the bias voltage undesirably increases. When the reference voltage has a positive temperature characteristic, the bias currents of the liquid crystal output amplifiers 131 to 134 can be kept constant to prevent a decrease in the driving capability of the amplifiers. This is not preferable because the level reference voltage becomes high.

As described above, for example, the reference voltage generation circuit 91
If the temperature is low, the reference voltage for the liquid crystal level will increase when the temperature is low, compensating for the decrease in the reaction speed of the liquid crystal panel, keeping the liquid crystal brightness constant, and allowing the reference voltage to be positive. When the temperature characteristic is provided, the bias current of the liquid crystal output amplifier can be kept constant and the driving capability of the amplifier can be prevented from being reduced. However, in the single reference voltage generation circuit 91, the negative temperature characteristic and the positive temperature characteristic Cannot be realized.

On the other hand, the power supply circuit 2 shown in FIG.
Reference numeral 22 denotes a liquid crystal level reference voltage generating circuit 11 having a negative temperature characteristic and generating a liquid crystal level reference voltage, and a bias voltage Vb having a positive temperature characteristic and supplied to the liquid crystal output amplifier. And a liquid crystal output amplifier reference voltage generating circuit 12 for obtaining the temperature characteristics of the liquid crystal panel 21 and the liquid crystal output amplifiers 131 to 13.
4 are simultaneously canceled with each other, whereby both the reduction in the brightness of the liquid crystal and the deterioration in the image quality are improved.

According to the above example, the following functions and effects can be obtained.

(1) Due to the nature of the liquid crystal panel 21, the reaction speed of the liquid crystal panel 21 is reduced by lowering the temperature,
Although the brightness is also reduced, since the liquid crystal level reference voltage generating circuit 11 has a negative temperature characteristic, when the temperature is low, the liquid crystal level reference voltage is increased to compensate for the decrease in the reaction speed of the liquid crystal panel. , Thereby keeping the liquid crystal brightness constant.

(2) When the temperature rises, the bias current in the liquid crystal output amplifiers 131 to 134 is reduced, and the driving capability of the liquid crystal output amplifier itself is reduced. Because of the temperature characteristics, the bias current of the liquid crystal output amplifier is kept constant, and the driving capability of the amplifiers 131 to 134 is prevented from being reduced.

(3) As described above, the liquid crystal brightness of the liquid crystal panel 21 is kept constant, and the liquid crystal output amplifiers 131 to 1
The image quality of the liquid crystal panel 21 can be improved by maintaining the bias current at 34 constant.

(4) Liquid crystal level reference voltage generating circuit 11
, And the positive temperature characteristic of the liquid crystal output amplifier reference voltage generating circuit 12 can be easily realized by adjusting the current mirror ratio of the current mirror circuit.

Although the invention made by the present inventor has been specifically described above, the present invention is not limited to this, and it goes without saying that various modifications can be made without departing from the gist of the invention.

For example, a liquid crystal level reference voltage generating circuit 1
1 and the reference voltage generating circuit 12 for the liquid crystal output amplifier,
A switch capable of changing the current mirror ratio can be provided. FIG. 8 shows a configuration example in that case.

N channel type MOS transistor Q8
5, Q86 are connected in series, and a current mirror circuit 80 is coupled thereto. This current mirror circuit 80 has p
Channel type MOS transistors Q81-1, Q81-
2, Q81-3, Q82-1, Q82-2, Q82-
3, and switches 88-1, 88-2, 87-1, 87
-2 are combined. The source electrodes of the p-channel MOS transistors Q81-2 and Q81-3 are coupled to the high-potential power supply Vdd via the corresponding switches 88-1 and 88-2, respectively. The p-channel MOS transistors Q82-2 and Q82-3 are connected to the high-potential-side power supply Vdd via the corresponding switches 87-1 and 87-2, respectively.
Is combined with The switches 88-1, 88-2, 87
-1 and 87-2 are driven and controlled by the output signal of the decoder 80. The decoder 80 decodes the output signal of the register 81. Further, p-channel MOS transistors Q83 and Q84 are connected in series, and an output voltage is obtained from this series connection node. The above switches 88-1,
The current mirror ratio in the current mirror circuit 80 is controlled by the states of 88-2, 87-1, and 87-2. For example, the switches 88-1 and 99-2 are turned off by the output signal of the decoder 80, and the switches 87-1 and 87-2 are turned off.
When 7-2 is turned on, the current mirror ratio is M = 1
/ 3. A negative temperature characteristic or a positive temperature characteristic can be obtained by the current mirror ratio.
, The temperature characteristic of the reference voltage generating circuit is determined. The information held in the register 81 is stored in the controller 2
23 can be changed. When the liquid crystal level reference voltage generation circuit 11 and the liquid crystal output amplifier reference voltage generation circuit 12 shown in FIG. 1 adopt a configuration that allows the current mirror ratio to be changed as shown in FIG. In accordance with the temperature characteristics of the liquid crystal panel 21 and the liquid crystal panel 21,
In addition, the temperature characteristics of the reference voltage generating circuit 12 for the liquid crystal output amplifier can be optimized.

In FIG. 8, an n-channel MOS
Only the transistors Q85 and Q86 are of the depletion type, and the others are of the enhancement type.

The liquid crystal level reference voltage generation circuit 11
Alternatively, the reference voltage generating circuit 12 for the liquid crystal output amplifier may be arranged outside the small liquid crystal controller LSI22.

In the above description, mainly the case where the invention made by the present inventor is applied to a small liquid crystal control LSI, which is a field of application as the background, has been described. However, the present invention is not limited to this. Can be widely applied to a circuit for driving.

The present invention can be applied on the condition that a power supply circuit capable of outputting at least a voltage used for driving a liquid crystal panel is included.

[0066]

The effects obtained by typical ones of the inventions disclosed in the present application will be briefly described as follows.

That is, due to the nature of the liquid crystal panel, the reaction temperature of the liquid crystal panel is reduced and the brightness is reduced by lowering the temperature. However, since the first reference voltage generating circuit has a negative temperature characteristic, the temperature is lowered. When it is low, the reference voltage for the liquid crystal level becomes high to compensate for the decrease in the reaction speed of the liquid crystal panel, thereby stabilizing the brightness of the liquid crystal. In addition, as the temperature rises, the bias current in the liquid crystal output amplifier decreases, and the driving capability of the liquid crystal output amplifier itself decreases. However, since the second reference voltage generating circuit has a positive temperature characteristic, the liquid crystal output amplifier has a positive temperature characteristic. , The bias current is stabilized, and the driving capability of the amplifier is prevented from lowering.
Thereby, the image quality of the liquid crystal panel can be improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating a configuration example of a power supply circuit included in a small liquid crystal controller LSI in a liquid crystal display device according to the present invention.

FIG. 2 is a block diagram illustrating an overall configuration example of the liquid crystal display device.

FIG. 3 is a circuit diagram illustrating a configuration example of a liquid crystal driver included in the small liquid crystal controller LSI.

FIG. 4 is a circuit diagram illustrating a configuration example of a liquid crystal level reference voltage generation circuit included in the power supply circuit.

FIG. 5 is a circuit diagram illustrating a configuration example of a reference voltage generation circuit for a liquid crystal output amplifier included in the power supply circuit.

FIG. 6 is a temperature characteristic diagram of a reference voltage generation circuit.

FIG. 7 is a circuit diagram illustrating a configuration example of a liquid crystal output amplifier included in the power supply circuit.

FIG. 8 is a circuit diagram of another configuration example of the liquid crystal level reference voltage generation circuit and the liquid crystal output amplifier reference voltage generation circuit.

9 is a circuit diagram showing a configuration example of a power supply circuit to be compared with the power supply circuit shown in FIG. 1;

FIG. 10 is a temperature characteristic diagram of a liquid crystal panel.

FIG. 11 is a temperature characteristic diagram of the liquid crystal output amplifier.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Reference voltage for liquid crystal level 12 Reference voltage generation circuit for liquid crystal output amplifier 21 Liquid crystal panel 22 Small liquid crystal control LSI 40, 50, 80 Current mirror circuit 121 Liquid crystal level boosting amplifier 131-134 Liquid crystal output amplifier 221 Liquid crystal driver 222 Power supply circuit 223 controller

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Naoki Miyamoto 3681 Hayano Mobara-shi, Chiba Hitachi Device Engineering Co., Ltd. (72) Inventor Katsuhiko Yamamoto 3681 Hayano Mobara-shi Chiba Prefecture Hitachi Device Engineering Co., Ltd. (72) Inventor Kazuya Endo 3681 Hayano, Mobara-shi, Chiba Pref. Hitachi Device Engineering Co., Ltd. (72) Inventor Kazuo Daimon 5-2-1, Josuihoncho, Kodaira-shi, Tokyo F-term in the semiconductor group of Hitachi, Ltd. (Reference) 2H093 NC01 NC03 NC57 ND44 5C006 AF50 BB11 BC03 BC12 BC20 BF25 BF27 BF34 BF38 BF43 EB05 FA19 5C080 AA10 BB05 DD20 FF03 JJ02 JJ03 JJ05 KK07

Claims (5)

[Claims] 1. A power supply circuit capable of outputting a voltage used for driving a liquid crystal panel, and a liquid crystal driver for driving the liquid crystal panel by supplying an output voltage of the power supply circuit to the liquid crystal panel. A liquid crystal driving circuit, wherein the power supply circuit has a negative temperature characteristic, a first reference voltage generation circuit for generating a liquid crystal level reference voltage, and a liquid crystal generated by the first reference voltage generation circuit. An output amplifier that forms a voltage used for driving the liquid crystal panel based on a level reference voltage; and a second reference voltage generator that has a positive temperature characteristic and obtains a bias voltage supplied to the output amplifier. And a circuit. 2. A power supply circuit capable of outputting a voltage used for driving a liquid crystal panel, and a liquid crystal driver for driving the liquid crystal panel by supplying an output voltage of the power supply circuit to the liquid crystal panel. A liquid crystal driving circuit, wherein the power supply circuit has a negative temperature characteristic, a first reference voltage generation circuit for generating a liquid crystal level reference voltage, and a liquid crystal generated by the first reference voltage generation circuit. A booster amplifier for boosting the level reference voltage, a ladder resistor for dividing the output voltage of the booster amplifier into a plurality of voltages having different levels, and a voltage divided by the ladder resistor. A plurality of output amplifiers for forming voltages used for driving the liquid crystal panel; and a bias voltage having a positive temperature characteristic and supplied to the plurality of output amplifiers. Liquid crystal drive circuit, wherein the second reference voltage generating circuit, that comprises a. 3. The first reference voltage generation circuit and the second reference voltage generation circuit.
A reference voltage generating circuit, a depletion type transistor, a current mirror circuit for obtaining a current corresponding to a predetermined current mirror ratio based on a current flowing through the depletion type transistor, and an output current of the current mirror circuit. And a transistor for converting a current mirror voltage into a voltage. A current mirror ratio of a current mirror circuit included in the first reference voltage generation circuit and a current mirror ratio of a current mirror circuit included in the second reference voltage generation circuit are included. 3. The liquid crystal driving circuit according to claim 1, wherein the values are set to different values. 4. The liquid crystal drive circuit according to claim 3, wherein said current mirror circuit includes a switch capable of changing a current mirror ratio. 5. A liquid crystal display device comprising the liquid crystal driving circuit according to claim 1, and a liquid crystal panel driven by the liquid crystal driving circuit.