JP2823384B2 - Liquid crystal display panel drive device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving device for a liquid crystal display panel, and more particularly to a power supply voltage boosting circuit mounted on a one-chip driver LSI.

[0002]

2. Description of the Related Art Conventionally, a driving device for a liquid crystal display panel includes a common signal driver for supplying a common signal to a common signal terminal of the liquid crystal display panel and a segment signal for supplying a segment signal to a segment signal terminal of the liquid crystal display panel. A driver composed of a plurality of driver LSIs is generally used. FIG. 3 shows a so-called three-chip driving device including three driver LSIs,
Wiring 24-digit 2-line STN type liquid crystal display panel of a diagram schematically showing the common signal terminal C ₁ -C common signal terminal C ₁ -C ₁₆ and the liquid crystal display panel 12 of the first driver LSI11 ₁₆ and are connected by 16 signal line group 13, the first segment signal of the driver LSI11 terminal S ₁ to S ₄₀ and the liquid crystal display panel 12 segment signal terminals S ₁ to S ₄₀ and 40 present the signal They are connected by a line group 14. Also, it is connected by a second driver LSI15 segment signal terminals S ₄₁ to S ₈₀ and the liquid crystal display panel 12 of the segment signal terminals S ₄₁ to S ₈₀ and 40 signal lines group 16, further, a third are connected by the segment signal terminals S ₈₁ to S ₁₂₀ and the liquid crystal display panel 12 of the segment signal terminals S ₈₁ to S ₁₂₀ and 40 pieces of the signal line group 18 of the driver LSI 17.

On the other hand, in order to reduce the cost of the liquid crystal display panel by reducing the number of components, a driving device for a liquid crystal display panel in which a common signal driver and a segment signal driver are integrated into one chip has been proposed. FIG. 4 is a diagram schematically showing wiring between a one-chip type driving device and an STN type liquid crystal display panel having 24 columns and 2 rows.
Is connected at one common signal terminal C ₁ -C ₁₆ and the liquid crystal display panel 12 of the common signal terminal C ₁ -C ₁₆ and the 16 signal line group 22, the common signal of the driver LSI21 terminal C ₁₇ -C ₃₂ And the common signal terminal C ₁₇ of the liquid crystal display panel 12
It is connected by -C ₃₂ and the 16 signal line group 23.
Also, the segment signal terminal S of the driver LSI 21
₁ splits the respective signal lines included in 60 pieces of signal lines 24 drawn out from to S ₆₀ to form a signal line group 24a and 24b, the signal line group 24a and the liquid crystal display panel 12
Segment signal terminals S _{1 to} S ₆₀ and the signal line group 24
b and the segment signal terminals S _{61 to} S of the liquid crystal display panel 12
₁₂₀ is connected.

[0004] By the way, a 24-digit, 2-line ST shown in FIG.
When the N-type liquid crystal display panel 12 is driven with a 1/16 duty and a 1/4 bias using a three-chip driving device, the display contrast setting voltage V _LCD becomes 4.5 volts (25 ° C.). Normally output voltage (power supply voltage) V
A power supply circuit 25 having a _DD of 5 volts is provided. Then, as shown in FIG. 5, the output terminals V _DD and V
By operating the knob of the variable resistor 26 connected in series between _SS , the display contrast setting voltage V _LCD
Is adjusted to a predetermined value, for example, 4.5 volts, the output voltage V _O of the variable resistor 26 is adjusted. As is clear from this figure, in the driving device of this example, the variable resistor 2
As the output voltage V _O of No. 6 is increased, the set voltage V _LCD of the display contrast can be reduced.

[0005] On the other hand, a 24-digit, 2-row S shown in FIG.
When the TN type liquid crystal display panel 22 is driven at 1/32 duty and 1 / 6.7 bias using a one-chip type driving device, the display contrast setting voltage V _LCD is 8.5.
Volts (25 ° C). In this case, the power supply voltage V _DD is 9
If a power supply circuit of volts is provided, the set voltage V _LCD of the display contrast can be adjusted in the same manner as described above. However, it is costly to prepare various power supply circuits according to the type and driving method of the liquid crystal display panel. For this reason, a power supply circuit 25 whose power supply voltage V _DD is usually 5 volts is connected to the driver LSI 21 and the driver LS as shown in FIG.
DC / DC converter 27 integrated in I21
Thus, the voltage is increased to a desired set voltage _VLCD . That is, the output voltage V _O of the variable resistor 26 is converted to −V _O by the DC / DC converter 27 and the power supply voltage V _DD is boosted by the potential difference V _O to obtain the display contrast setting voltage V _LCD .

[0006]

However, the DC /
According to the booster circuit using the DC converter, as the output voltage V _O of the variable resistor 26 increases, the display contrast setting voltage V _LCD also increases. Therefore, when driving the STN type liquid crystal display panel 12 having 24 columns and 2 rows using a three-chip type driving device (as described above, as the output voltage V _O of the variable resistor 26 increases, the display contrast increases. “The set voltage V _LCD becomes smaller” means that the relationship between the operation direction of the knob of the variable resistor 26 and the contrast of the liquid crystal display panel is reversed, and it is inconvenient for a user using both types of devices.

[0007] In the above, the ST of 24 columns and 2 lines is used.
The drive device of the N-type liquid crystal display panel has been described as an example. However, regardless of the size and type of the liquid crystal display panel, a drive device of a liquid crystal display panel without a booster circuit and a DC / DC
A liquid crystal display panel driving device provided with a converter as a booster circuit has the same disadvantages as described above.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned disadvantages, and has as its object to provide a user-friendly liquid crystal display panel driving apparatus without changing the configuration of a power supply circuit. It is.

[0009]

In order to achieve the above object, the present invention provides a common signal driver for supplying a common signal to at least a common signal terminal of a liquid crystal display panel, and a segment signal for a segment signal terminal of the liquid crystal display panel. Driver comprising a segment signal driver for supplying a voltage and a booster circuit for boosting a power supply voltage (V _DD ) supplied from an external power supply circuit to obtain a set voltage (V _LCD ) for a desired display contrast. It includes a LSI, apparatus for driving a liquid crystal display panel to be adjusted by the variable resistor input voltage (V _O) is provided in the power supply circuit to the booster circuit, a differential amplifier circuit and the difference the booster circuit configured to include a plurality of external resistors determining the reference voltage (Vi ₁₎ and the gain of the dynamic amplifier, the input to be adjusted by the variable resistor Adjust the value of the external resistor so that the output voltage of the differential amplifier circuit (V _OUT) rises from the negative voltage according to increasing pressure of (V _O) from zero, the supply voltage and (V _DD) The display contrast setting voltage (V _LCD ) is obtained from the difference from the output voltage (V _OUT ) of the differential amplifier circuit.

[0010]

[Action] According to the configuration, the variable resistor the output voltage V _OUT of the differential amplifier circuit according to raise the input voltage V _O to the booster circuit is adjusted from zero by the rising As the external resistance from the negative voltage Is adjusted to obtain the display contrast setting voltage V _LCD from the difference between the power supply voltage V _DD and the output voltage V _OUT of the differential amplifier circuit. Is the same as the case of using a driving device without a booster circuit. Therefore, a user who uses both a liquid crystal display device without a booster circuit and a liquid crystal display device with a booster circuit has the same feeling of use, and is easy to use.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a circuit diagram of a liquid crystal display panel driving device according to the present invention, and FIG. 2 is an input / output characteristic diagram of a booster circuit. The liquid crystal display panel driving device of the present invention is integrally mounted in the driver LSI integrated into one chip shown in FIG.

As shown in FIG. 1, the liquid crystal display panel driving device of the present invention comprises an operational amplifier 1 which is a differential amplifier circuit and external resistors R ₁ , R ₂ , which determine the gain of the operational amplifier 1.
R ₃ and R ₄ , external resistors R ₅ and R ₆ for determining the reference voltage Vi ₁ of the operational amplifier 1, and a DC / DC converter 2 for generating a negative drive voltage of the operational amplifier 1. Then, a reference voltage V _i1 [= {R ₆ / (R ₅ + R ₆ )} V _DD ] obtained by dividing the power supply voltage V _DD by the external resistors R ₅ and R _{6 is supplied} to the operational amplifier via the external resistor R _1. The output voltage V _O of the variable resistor 26 provided in the power supply circuit 25 is connected to the positive input terminal of the operational amplifier 1 via the external resistor R ₂ . The power supply circuit 25
Power supply voltage V _DD supplied from is connected to the positive power supply terminal of the operational amplifier 1, -V _DD operational amplifier 1 obtained by polarity converting the power supply voltage V _DD at the DC / DC converter 2
Is connected to the minus power supply terminal.

In the circuit of FIG. 1, the output voltage V _OUT of the operational amplifier 1 is V _OUT = − (R ₃ / R ₁ ) Vi ₁ + {(R ₁ + R ₃ ) / R ₁ ｝ {R ₄ / (R
₂ + R ₄ )｝ V _O, and by appropriately selecting the external resistors R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , and R ₆ , as shown in FIG. When the voltage V _O is zero, the output voltage V _{OUT of the} operational amplifier 1 becomes a negative voltage, and the variable resistor 26
, The absolute value of the output voltage V _OUT of the operational amplifier 1 can be reduced as the output voltage V _O increases from zero. On the other hand, the display contrast setting voltage V _LCD is obtained by taking the potential difference (V _LCD = V _DD −V _OUT ) between the power supply voltage V _DD and the output voltage V _OUT of the operational amplifier 1, so that the driving without the booster circuit is performed. Similarly to the device (see FIG. 5), when the knob of the variable resistor 26 is operated in the direction in which the output voltage V _O increases, the display contrast setting voltage V
_{The LCD} will drop.

As described above, according to the liquid crystal display panel driving device of the embodiment, the relationship between the operation direction of the knob of the variable resistor 26 and the contrast of the liquid crystal display panel is different from the case where the driving device without a booster circuit is used. Since they are the same, usability is improved. Further, the driving voltage of the operational amplifier 1 −V _DD
Is a DC / DC mounted on the driver LSI 21 in advance.
Since the power is generated by the converter 2, there is no need to separately provide a power supply circuit for driving the operational amplifier, and the operation can be performed at low cost.

In the above embodiment, the operational amplifier is used as the differential amplifier circuit. However, the differential amplifier circuit can be configured using another device.

[0016]

As described above, according to the liquid crystal display panel driving device of the present invention, as the input voltage V _O to the booster circuit adjusted by the variable resistor increases from zero, the output voltage of the differential amplifier circuit increases. The value of the external resistor was adjusted so that V _OUT increased from a negative voltage, and the display contrast setting voltage V _LCD was obtained from the difference between the power supply voltage V _DD and the output voltage V _OUT of the differential amplifier circuit. In addition, the relationship between the operation direction of the knob of the variable resistor and the contrast of the liquid crystal display panel becomes the same as in the case where a driving device without a booster circuit is used, and the usability is improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a booster circuit according to the present invention.

FIG. 2 is an output characteristic diagram of the booster circuit according to the present invention.

FIG. 3 shows a first example of a liquid crystal display panel driving device according to the related art.
It is a block diagram showing an example.

FIG. 4 shows a second example of a conventional liquid crystal display panel driving device.
It is a block diagram showing an example.

FIG. 5 is an explanatory diagram of a power supply unit of a liquid crystal display panel driving device according to the related art.

FIG. 6 is an explanatory diagram of a booster circuit according to the related art.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 operational amplifier (differential amplifier circuit) 2 DC / DC converter 12 liquid crystal display panel 21 driver LSI 26 variable resistor V _DD power supply voltage V _O input voltage to boost circuit (output voltage of variable resistor) Vi ₁ reference voltage V _OUT Output voltage of differential amplifier circuit V Setting voltage for _LCD display contrast R _{1 to} R ₆ External resistance

Claims (1)

(57) [Claims] 1. A common signal driver for supplying a common signal to at least a common signal terminal of a liquid crystal display panel, a segment signal driver for supplying a segment signal to a segment signal terminal of the liquid crystal display panel, and an external power supply circuit. A driver LSI integrated on a single chip including a booster circuit for boosting a power supply voltage (V _DD ) to obtain a desired display contrast set voltage (V _LCD ) is provided. The input voltage (V _O ) to the booster circuit is increased. In a liquid crystal display panel driving device adjusted by a variable resistor provided in the power supply circuit, the booster circuit includes a differential amplifier circuit and a plurality of circuits for determining a reference voltage (Vi ₁ ) and a gain of the differential amplifier circuit. And an external resistor, and the differential voltage is increased as the input voltage (V _O ) adjusted by the variable resistor increases from zero. The value of the external resistor is adjusted so that the output voltage (V _OUT ) of the width circuit rises from a negative voltage, and the difference between the power supply voltage (V _DD ) and the output voltage (V _OUT ) of the differential amplifier circuit is calculated. A driving device for a liquid crystal display panel, wherein a set voltage ( _VLCD ) of the display contrast is obtained.