JPH08272337A - Display control circuit - Google Patents

Abstract

PURPOSE: To continuously transfer a command from a CPU side without caring for a charge-up period of a capacitor for compensating a display limit due to power of an integrated power source circuit and to dissolve display malfunction immediately after a liquid crystal power source circuit is turned on. CONSTITUTION: In a display control circuit of an LCD driver IC incorporating the liquid crystal power source circuit, a liquid crystal driving voltage 15 and the grounded voltage 10 are divided into plural potential 11-14. Respective divided voltages are connected to V/F circuits 110, and their outputs are sent to a comparator circuit 103, and the output signal 204 of the circuit 103 and a display on-command signal sent from the CPU are ANDed. A voltage selection circuit 108 fixes respective supply potential to an output driver circuit to the grounded level while until a display on-signal is inputted when a liquid crystal power source on-command is executed, and supplies prescribed potential to the output driver circuit 109 simultaneously when the display on-signal 205 is inputted, and performs operation control of a liquid crystal display device 114.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display control circuit of an LCD driver IC containing a liquid crystal power supply circuit.

[0002]

2. Description of the Related Art As a recent trend, an LCD driver IC
Is a CR oscillator circuit and a display RA for added value.
M, a liquid crystal power supply circuit and other peripheral circuits are designed. Regarding the liquid crystal power supply circuit, conventionally, an external power supply was used, so that a power supply suitable for the liquid crystal display device could be selected. However, the LCD driver I incorporating the liquid crystal power supply circuit
In the case of C, the display capability is limited by the capability of the built-in power supply circuit, and therefore it may not always be possible to supply power suitable for the liquid crystal display device. To compensate for this, normally, as in the conventional example shown in FIG.
1), 22 (V2), 23 (V3), 24 (V4) and 1
Each 321 (capacitor C) is connected between 0 (VDD ground), and when the power exceeding the capacity of the liquid crystal power supply circuit built in the LCD driver IC is consumed, each potential is charged from the charged capacitor C. I am trying to supply it.

In the case of an LCD driver IC with a built-in liquid crystal power supply, since the liquid crystal power supply circuit for the capacitor C is turned on and charge-up is started at the same time, the charge-up period of the capacitor C is maintained for a certain period after the liquid crystal power supply circuit is turned on. As a result, the voltage values of V1, V2, V3 and V4 become unstable as shown in FIG. 7, for example. According to FIG. 7, a stabilization time is required until the output voltage stabilizes after the power supply circuit is turned on, and the relationship of V1>V2>V3> V4 does not hold in the initial state.

In the case of FIG. 7, 21 (V1), 22 (V
2), the period until the voltage of 23 (V3), 24 (V4) stabilizes is determined by the capability of 110 (V / F circuit) and 321 (external capacitor C), so The waveforms of V1, V2, V3 and V4 are not constant because they are affected by deviations, manufacturing variations, the capacitance value of the external capacitor C, and the usage environment.

Further, as shown in FIG. 1, 114 (liquid crystal display device) is 10 (VD) by 108 (voltage select circuit).
D), 21 (V1), 22 (V2), 23 (V3), 2
Since the blinking of the display data is controlled by selecting the potential of 4 (V4) and 15 (V5), when the display ON command is executed from the CPU during this charge-up period, it is supplied to the liquid crystal display device. V1, V2, V3, V4
Since the voltage is unstable, the output data is not normally displayed on the liquid crystal display device, and in general, the liquid crystal display device may not display a normal screen until the capacitor C is sufficiently charged up. is there.

As an example of conventional measures, the timing of the command transferred from the CPU side is set to be slightly longer than the charge-up period of the capacitor C from the execution of the liquid crystal power supply circuit ON command to the execution of the display ON command, so that the software is used. It corresponded.

[0007]

In the above-mentioned conventional method, the input delay timing of the power ON command and the display ON command fluctuates due to variations in the value of the capacitor C and manufacturing of the LCD driver IC. Since the timing must be set individually so that it does not feel uncomfortable with the operation delay (several hundreds of ms), it is necessary to pay attention to the command delay time setting and CPU There was a problem that commands could not be continuously transferred from the side and wasteful time was consumed.

The object of the present invention is not to worry about the value of the capacitor C and the period of charge-up due to manufacturing variations,
It is an object of the present invention to provide a display control circuit of an LCD driver IC with a built-in liquid crystal power supply circuit, which can continuously transfer commands from the CPU side and eliminates a display malfunction of the liquid crystal display device immediately after the liquid crystal power supply circuit is turned on.

[0009]

In a display control circuit for displaying a liquid crystal display device, there is provided a power supply voltage generating circuit for supplying a plurality of potentials to the liquid crystal display device, and a detection circuit for detecting the plurality of potentials. And a logic circuit that takes the logic of the output of the detection circuit and a display permission signal that permits display of data on the liquid crystal display device, and supply of a potential to the liquid crystal display device by the output of the logic circuit. Is controlled.

Further, the detection circuit is characterized by having a comparison circuit for comparing a reference voltage with the plurality of potentials.

Alternatively, the detection circuit has a comparison circuit for comparing the potentials of the plurality of potentials.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of a display control circuit of an LCD driver IC of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the display control circuit of the LCD driver IC of the present invention. Liquid crystal power supply voltage 15 (V5) and 10 (ground level VDD) generated by an external power supply or a booster circuit, a voltage adjusting circuit, etc. inside the IC
Is divided by 301 and 302 (resistive elements R and R '),
11 (V1), 12 (V) that match the characteristics of the liquid crystal display device
2), voltage values of 13 (V3) and 14 (V4) are generated. Here, the resistance elements R and R'may use the on resistance of polysilicon or a transistor, and the display level is stabilized by matching the resistance values. 110 (V / F circuit) is provided for each of the V1, V2, V3 and V4 potentials divided by the resistance elements R and R'as reference voltages. Since the V / F circuit uses a display clock of about several tens of kHz, it does not have to have a fast response time, but a liquid crystal display device displays a liquid crystal display device having a larger allowable current and a larger display area. If the current supply capacity is high, the capacitance value of 321 (external capacitor C) can be small, so that the charge-up period of the capacitor C when the liquid crystal power supply circuit is ON can be short. However, since the current consumption increases, it is necessary to design the size for the target of each LCD driver IC.

One of the outputs of the 110 (V / F circuit) is to 108 (voltage select circuit), one is to 103 (comparator circuit), and the other is 209 (external output terminal).
Connect to each.

A reference numeral 321 (external capacitor C) is connected to 209 (external output terminal). The purpose of the 321 (external capacitor C) is to increase the power of the liquid crystal display device to the
It is provided to supplement the electric power when the capacity of 0 (V / F circuit) is exceeded, and the capacitance value is individually set by the capacitance of the liquid crystal display device. For small and medium capacity LCDs,
C = about 0.01 to 10 μF is selected.

The 103 (comparator circuit) is shown in FIG.
The first embodiment of the comparator circuit is shown in FIG. In FIG. 2, the resistance element 3 is provided between the 10 (VDD) and 15 (V5).
11 (r1), 312 (r2), 313 (r3), 31
4 (r4) and 315 (r5) are provided and the voltage is divided to 31 (V
1 '), 32 (V2'), 33 (V3 '), 34 (V
4 ') Each voltage value is obtained. Here, the resistance elements r1 and r
2, r3, r4, and r5 are resistance elements having the same structure as the resistance elements R and R'for matching with the resistance elements R and R '.

The V1 ', V2', V3 'and V4' potentials are 21 (V1), 22 (V2) and 23 (V, respectively).
3) and 24 (V4) potentials, a comparator circuit is provided for each of them, and V1 and V1 ′, V2 and V are provided.
2 ', V3 and V3', V4 and V4 'are compared, and (V1>
V1 ') * (V2>V2') * (V3> V3 ') * (V
The output of each comparator circuit is connected to each input terminal of 112 (four-input AND circuit) so that the logic becomes true when 4> V4 ′).

Here, the resistance value of each of the resistance elements is not affected by manufacturing variations, and V1 ≧ V1 ′, V2 ≧ V2 ′, V
It is necessary to set so that the relationship of 3 ≧ V3 ′ and V4 ≧ V4 ′ can be maintained. For example, when R = R 'in FIG.
r1 <R, r2 = r3 = r4 = R, r5> R, r1 + r
It is sufficient to set 5 = 2 · R.

The difference between the resistance values of r1 and R is due to manufacturing variations. However, if the resistance elements are formed on the same chip with the same structure, it is easy to match the resistance values, and r1 is more than necessary. It is not necessary to have a difference between R and R.

V1, V2 due to the difference in the resistance value of r1 <R
Considering the influence of the comparator circuit of V3 and V4 on the judgment level, it is not necessary for each voltage value of V1, V2, V3 and V4 to rise 100%, and V1, V2, V3 and V4
If the order of the four potentials is substantially maintained, the liquid crystal display device does not cause malfunction display, and therefore the potentials of V1, V2, V3, and V4 may be about 90% of the final value. Therefore, r1 =
It can be set to about 0.9 · R.

Next, in FIG. 1, the display ON is transferred from 104 (CPU) via 201 (external data bus).
Commands are sent via 105 (CPU interface) and via internal data bus by 106 (decoder).
(Display ON command signal) is generated. The 203 (display ON command signal) and the output 204 generated by the 103 (comparator circuit) are logically ANDed by 107 (2-input AND circuit). After executing the liquid crystal power supply circuit ON command, 21 (V1), 22 (V2), 23 (V
3), When the potential level of 24 (V4) becomes true by 103 (comparator circuit), 205 (display ON signal level) is output from 107 (AND circuit) by the logical product with 203 (display ON command signal). 108 (voltage select circuit).

The 108 (voltage select circuit) has the voltage values 10 (VDD), 21 (V1) and 22 (V).
2), 23 (V3), 24 (V4), 15 (V5) 2
Each voltage level is selectively supplied to 109 (output driver circuit) in synchronization with 06 (display clock signal) and depending on the presence or absence of display data. In addition, in 108 (voltage select circuit), when the liquid crystal power ON command is executed, 2
Until the input of 05 (display ON signal), each potential supplied to the output driver circuit is set to 10 (VDD) level, and each potential is fixed so that the liquid crystal display device does not erroneously display. 1 when 205 (display ON signal) is input
09 (output driver circuit) is supplied with a predetermined potential,
4 (liquid crystal display device) can be operated.

In the first embodiment as described above, V1, V
Although a comparator circuit was provided at each V / F circuit output section of 2, V3 and V4 potentials, if the critical potential was clarified at the design stage, it would be compared to all V1, V2, V3 and V4 potentials. It is not necessary to provide a circuit, and the same effect can be obtained even if the V / F circuit output of the critical potential is provided at only one place, and the chip size can be reduced. In this case, the resistance elements r1, r2, r3 of the comparator circuit section
r4 and r5 are the same as in the first embodiment.

FIG. 4 shows a second embodiment of the comparator circuit in FIG.

In the first embodiment of the comparator circuit, V
1, V2, V3, V4 has been constructed by focusing on the fact that each voltage reaches the set voltage. In the second embodiment shown in FIG. 4, the potentials V1, V2 generated by the liquid crystal power supply circuit are set. , V3 and V4 are compared, V1>V2> V3
When the relationship of> V4 is established, it is in a displayable state.

FIG. 4 shows a second embodiment of the comparator circuit. In FIG. 4, one 111 (comparator circuit) has a reference potential of 21 (V1) and an input potential of 22 (V).
2), the H level is output when the relationship of V2> V1 is established, and the reference potential is 22 (V
2), the input potential is set to 23 (V3), the H level is output when V3> V2, the reference potential is set to 23 (V3) and the input potential is set to 24 (V4) for one comparator circuit, and V4>
In case of V3, H level is output and (V1> V2) * (V
The output of each comparator circuit is set to 113 (3 inputs A) so that the logic becomes true when 2> V3) * (V3> V4).
ND circuit) to each input terminal.

The connection and operation other than 103 (comparator circuit block) are the same as those in the first embodiment of the comparator circuit.

In a second embodiment of the comparator circuit, V
When the relationship of 1>V2>V3> V4 is established, the display malfunction is less likely to occur, and the circuit is configured with a focus on it.

In this case, each V / F output voltage is equal to the set voltage V
The display becomes possible without reaching 1, V2, V3, V4, but this does not cause a problem because a display malfunction does not actually occur.

[0030]

As described above, according to the present invention,
Regardless of the capacitance value of the capacitor C connected between the plurality of potentials for driving the liquid crystal, the liquid crystal display device becomes ready for display in the shortest time after execution of the display ON command. Further, since the comparator circuit is formed on the same chip, it can operate reliably without being affected by manufacturing variations and environmental changes, and display malfunctions can be eliminated.

In the interface with the CPU, C
This has the effect of eliminating wasted time due to the command output waiting state on the PU side and being able to transfer commands continuously.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a liquid crystal power supply circuit and a display control circuit of an LCD driver IC that is an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a first embodiment of a comparator circuit.

FIG. 3 is a potential transition diagram of V1, V2, V3, and V4 after the liquid crystal power supply circuit is turned on in the first embodiment of the comparator circuit.

FIG. 4 is a circuit diagram showing a second embodiment of a comparator circuit.

FIG. 5 is a potential transition diagram of V1, V2, V3, and V4 after the liquid crystal power supply circuit is turned on in the second embodiment of the comparator circuit.

FIG. 6 is a circuit diagram of a conventional liquid crystal power supply circuit.

FIG. 7 shows V1, V2, V3 and V4 after the liquid crystal power supply circuit is turned on.
Potential transition diagram.

[Explanation of symbols]

10 is VDD (ground), 11 is divided potential V1, 12
Is a divided potential V2, 13 is a divided potential V3, 14 is a divided potential V4, 15 is V5 (liquid crystal power supply voltage), 21 is a V / F circuit output potential V1, 22 is a V / F circuit output potential V2, 23 Is V / F circuit output potential V3, 24 is V / F circuit output potential V
4, 31 are comparator reference potentials V1, 32 are comparator reference potentials V2, 33 are comparator reference potentials V3,
34 is a comparator reference potential V4, 101 is a voltage dividing circuit,
102 is a V / F circuit block, 103 is a comparator circuit block, 104 is a CPU, 105 is a CPU interface, 106 is a command decoder, and 107 is a 2-input A.
ND, 108 is a voltage select circuit block, 109 is an output driver circuit block, 110 is a V / F circuit, 111
Is a comparator circuit, 112 is a 4-input AND, 113 is a 3-input AND, 114 is a liquid crystal display device, 115 is a reference voltage circuit, 201 is an external data bus, 202 is an internal data bus, 203 is a display ON command signal, and 204 is Comparator circuit output signal, 205 is a display ON / OFF signal,
Reference numeral 206 is a display timing clock signal, 207 is an output driver supply potential, 208 is a liquid crystal display drive voltage, 209
Is an external output terminal, 301 is a dividing resistor R, 302 is a dividing resistor R ', 311 is a dividing resistor r1, 312 is a dividing resistor r.
2, 313 are division resistors r3, 314 are division resistors r4, 3
Reference numeral 15 is a dividing resistor r5, and 321 is an external capacitor C.

Claims (3)

[Claims] 1. A display control circuit for displaying a liquid crystal display device, comprising a power supply voltage generation circuit for supplying a plurality of potentials to the liquid crystal display device, a detection circuit for detecting the plurality of potentials, and the detection circuit. A logic circuit that takes the logic of an output of the circuit and a display permission signal that permits display of data on the liquid crystal display device is provided, and supply of a potential to the liquid crystal display device is controlled by the output of the logic circuit. A display control circuit characterized by the above. 2. The display control circuit according to claim 1, wherein the detection circuit has a comparison circuit that compares a reference voltage with the plurality of potentials. 3. The display control circuit according to claim 1, wherein the detection circuit has a comparison circuit for comparing the potentials of the plurality of potentials.