JP3448495B2 - LCD drive integrated circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal drive integrated circuit capable of adjusting display contrast. 2. Description of the Related Art FIG. 5 is a circuit block diagram showing a conventional display contrast adjusting method using a liquid crystal driving integrated circuit. In FIG. 5, a liquid crystal panel (101) has
It is formed by arranging a plurality of segment electrodes and a plurality of common electrodes in a matrix. LCD panel (10
The segment drive signal and the common drive signal are applied to the plurality of segment electrodes and the plurality of common electrodes in 1), respectively, and only the matrix intersection where the potential difference between the segment drive signal and the common drive signal is equal to or more than a specific value is lit. The liquid crystal driving integrated circuit (102) drives a liquid crystal panel (101) for display. In the liquid crystal drive integrated circuit (102), each connection point of the four series resistors R1 is connected to terminals (103) to (107). The terminal (103) is a terminal to which a reference voltage VLCD0 that determines the peak values of the segment drive signal and the common drive signal is applied, and the terminal (107) is a terminal for commonly grounding all the components of the liquid crystal drive integrated circuit (102). is there. Therefore, the space between the reference voltage VLCD0 and the ground voltage Vss is divided into four,
Terminals (103) (104) (105) (106) (10
The voltages of 7) are VLCD0, VLCD1, and VLCD, respectively.
2, VLCD3, and Vss. Common drive circuit (10
8) is the voltage VLCD0, VLCD1, VLCD3, Vs
s is applied to generate a common drive signal.
The common drive signal changes between the reference voltage VLCD0 and the ground voltage Vss when instructing to turn on the liquid crystal panel (101), and changes the voltages VLCD1 and VLCD3 when instructing to turn off the liquid crystal panel (101). Change between. That is, in this case, the common drive signal has a バ イ ア ス bias drive waveform. On the other hand, the segment drive circuit (109) generates a segment drive signal by applying the voltages VLCD0, VLCD2, and Vss. When instructing to turn on the liquid crystal panel (101), the segment drive signal changes between the reference voltage VLCD0 and the ground voltage Vss in a phase opposite to that of the lighting drive common drive signal, and the liquid crystal panel (10).
When the light-off instruction of 1) is instructed, the voltage VLCD2 remains unchanged. The reference voltage VLCD0 is applied to the liquid crystal panel (10
The display contrast (display difference between light-on and light-off) of 1) is determined. That is, the display contrast of the liquid crystal panel (101) can be optimized by varying the reference voltage VLCD0 and changing the amplitudes of the common drive signal and the segment drive signal. The reference voltage generation circuit (110) receives the reference voltage V
LCD0 is applied to the terminal (103). In the reference voltage generating circuit (110), the resistor (111) and the variable resistor (112) are connected in series between the power supply Vdd and the ground Vss. The operational amplifier (113) is connected to the resistor (11
1) and a reference voltage VLCD0 equal to the connection point voltage of the variable resistor (112) is output. If the impedance of the four series resistors R1 is larger than the load impedance of the liquid crystal panel (101), the voltages VLCD1, VLCD
2. There is a high possibility that the VLCD 3 will not be determined. Therefore, the operational amplifier (1) having a small output impedance
Use 13). Also, terminals (103) to (107)
A method of externally connecting a resistor between the resistors to form a parallel resistor with the four series resistors R1 to reduce the impedance on the series resistor R1 side is also applicable. Reference voltage generation circuit (1
In 10), a control signal for changing the value of the variable resistor (112) is supplied from an external controller. Therefore, the reference voltage VLCD0 is changed under the control of the external controller to adjust the display contrast of the liquid crystal panel (101). However, in the case of FIG. 5, it is necessary to externally connect the reference voltage generating circuit (110) to the liquid crystal driving integrated circuit (102). That is, since the reference voltage generating circuit (110) has a large number of elements, there is a problem that the cost of the electronic device is hindered. Furthermore, since a specific port of the external controller is occupied for outputting a control signal, there is a problem that the function of the electronic device is hindered. FIG. 6 is another circuit block diagram showing a display contrast adjusting method using a conventional liquid crystal driving integrated circuit, which is intended to solve the problem of FIG. . The liquid crystal panel (101) shown in FIG.
Common drive circuit (108), segment drive circuit (10
The description of 9) is omitted. In the liquid crystal driving integrated circuit (201), each connection point of the four series resistors R1 is connected to the terminals (202) to (206) for the same reason as in FIG. The terminal (202) is a power supply terminal to which the power supply Vdd is applied.
The regulator (207) is a constant voltage VR based on the power supply Vdd.
Output F. The operational amplifier (208) has a + terminal connected to the constant voltage VRF, a − terminal connected to the terminal (209), and an output terminal connected to the terminal (206). The value of the current IR flowing through the-terminal of the operational amplifier (208) can be adjusted under the control of the internal controller. Both ends of the three series resistors R2, R3 and R4 are externally connected to the terminals (202) and (206), and the resistor R3 is externally connected to the terminal (209). The voltage VLCD4 is expressed as ((Ra + Rb) / R
a) It is represented by VRF + IR · Rb. Therefore, the current IR is controlled by the control of the internal controller, and the voltage VLC
D4 was changed to adjust the display contrast of the liquid crystal panel (101). However, in the case of FIG. 5, the external elements of the liquid crystal driving integrated circuit (201) need only be the resistors R2, R3, and R4. However, due to the point that the resistance values of the resistors R2, R3, and R4 vary individually. There has been a problem that the ratio of the voltages Ra and Rb deviates from an expected value, so that an appropriate display contrast cannot be realized. Eventually, the resistance R is controlled by the external controller.
2, the variation of the resistance values of R3 and R4 must be corrected, and the same problem as that of FIG. SUMMARY OF THE INVENTION It is an object of the present invention to provide a liquid crystal driving integrated circuit which does not require external elements and can adjust display contrast. SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and is intended to display and drive a liquid crystal panel from each connection point of a plurality of first series resistors. An integrated circuit for generating a liquid crystal drive voltage, wherein said plurality of first
In a liquid crystal drive integrated circuit for adjusting a display contrast of the liquid crystal panel by varying a reference voltage applied to one end of the series resistor, a plurality of second series resistors connected to a power supply;
A reference voltage generating circuit that includes a selection circuit that derives any one of the connection point voltages of the plurality of second series resistors, and that generates the reference voltage based on an output of the selection circuit; A first switch circuit for selectively connecting one end of the series resistor to a power supply or the reference voltage generation circuit, a second switch circuit for connecting or disconnecting the plurality of second series resistors to or from a power supply, A circuit for permitting or stopping the operation, wherein when the reference voltage generation circuit is operated, the first switch circuit is turned off and the second switch circuit is turned on, and when the reference voltage generation circuit is turned off, The first switch circuit is turned on and the second switch circuit is turned off. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be specifically described with reference to the drawings. FIG. 1 is a circuit diagram showing a liquid crystal driving integrated circuit according to the present invention. In FIG. 1, a liquid crystal driving integrated circuit (1) shown by a broken line has a terminal (2) for applying a power supply voltage VLCD for driving the liquid crystal, a terminal (3) for applying a ground voltage Vss,
Connection point voltages VLCD0, VLC of four series resistors R1
Terminal for outputting D1, VLCD2 and VLCD3 (4)
(5) There are (6) and (7). The lower ends of the four series resistors are connected to a terminal (3) for commonly grounding the internal elements of the liquid crystal drive integrated circuit (1). In the liquid crystal driving integrated circuit (1), 1
The two series resistors R5, R6 and R7 are connected between the power supply terminal (2) and the ground terminal (3), and the twelve series resistors R5
5, each of the connection points of R6 and R7 is divided by each resistance value.
The voltages V0 to V10 are generated. 12 series resistors R
5, R6, R7 are integrated on a single semiconductor substrate,
The twelve resistance values vary at the same rate. That is, the voltage V0
To V10 does not change, and a stable reference voltage VLCD0 can be obtained. 11 transmission gates T
One end of G0 to TG10 has 12 series resistors R5, R6,
R7 is connected to each connection point, and control signals CA0 to CA10
To derive any one of the eleven voltages V0 to V10. The control signals CA0 to CA10 are high-level (logical value "1") or low-level (logical value "0") binary signals, and only one of the control signals is at the high level. The operational amplifier (8) has a + (non-inverting input) terminal commonly connected to the other ends of the transmission gates TG0 to TG10.
A reference voltage VLCD0 for liquid crystal display is output based on a voltage derived from any one of G10. Here, when the impedance of the four series resistors R1 is larger than the load impedance of the liquid crystal driving circuit, the liquid crystal panel, or the like in the subsequent stage, the voltage V is decreased with the decrease in the current flowing through the series resistor R1.
There is a high possibility that LCD1, VLCD2, and VLCD3 will not be determined. Therefore, the operational amplifier (8) having a low output impedance is used in consideration of the load impedance. Further, an external resistor is connected between any combination of the terminals (3), (4), (5), (6), and (7) to form a parallel resistor with the four series resistors R1, and the series resistor R1 May be used. 5 appearing at each connection point of the four series resistors R1
Voltage VLCD0, VLCD1, VLCD2, VLC
D3 and Vss are applied to the common drive circuit and the segment drive circuit as in FIG. The liquid crystal panel is supplied with a common drive signal and a segment drive signal, and displays characters and the like. Note that the subsequent stage of the four series resistors R1 is the same as that of FIG. 5, and the description and description thereof in FIG. 1 are omitted. A transmission gate TG11 (corresponding to a first switch circuit according to claim 1) is connected between the power supply terminal (2) and the output terminal of the operational amplifier (8), and has four series resistors R1. One of the power supply VLCD and the reference voltage (V0 to V10) is applied to one end. The transmission gate TG12 (corresponding to a second switch circuit according to claim 1) is connected to a power supply terminal (2).
And one end of the resistor R5 to apply or cut off the power supply voltage VLCD to the 12 series resistors R5, R6, and R7. Transmission gate TG11,
The TG 12 performs a complementary operation with a signal L4 based on control data D4 described later. The operation of the operational amplifier (8) is controlled by the signal L4. For example, the level of the control electrode of the current source transistor constituting the operational amplifier (8) may be controlled by the signal L4. Specifically, the operational amplifier (8) outputs the signal L4
When the signal L4 has one logical value, the current source transistor is turned on to perform the operation, and when the signal L4 has the other logical value, the current source transistor is turned off and the operation is stopped. When the operational amplifier (8) is operating, the transmission gate T
G11 and TG12 turn off and on, respectively, and when the operational amplifier (8) stops operating, the transmission gates TG11 and TG12 turn on and off, respectively. FIG. 2 is a circuit block diagram showing a part of a liquid crystal driving integrated circuit for generating control signals CA0 to CA10. In the embodiment of the present invention, the liquid crystal driving integrated circuit (1) has an interface function between integrated circuits that permits only specific input data. The three terminals (9), (10), and (11) are external input terminals for determining the control signals CA0 to CA10. The operation enable signal CE, the clock signal CL, and the serial Data DI is supplied. More specifically, the serial data DI is a serial connection of unique address data for identifying the liquid crystal driving integrated circuit (1) and control data for determining the control signals CA0 to CA10. The interface circuit (12) detects the states of the operation permission signal CE, the clock signal CL, and the serial data DI, and outputs the control data SDI and the clock signal SCL.
More specifically, the interface circuit (12) detects address data coincidence when the operation permission signal CE is at a low level, and outputs control data when the operation permission signal CE changes to a high level. The operation of the interface circuit (12) will be described with reference to the time chart of FIG. First, when the operation permission signal CE is at a low level, the interface circuit (1
2) It is detected whether or not the address data B0 to B3 and A0 to A3 supplied in synchronization with the clock signal CL are unique values predetermined in the liquid crystal driving integrated circuit (1). Next, the address data B0 to B3, A0 to A3
Coincides with the eigenvalue of the liquid crystal driving integrated circuit (1), and when the operation permission signal CE changes to a high level, the interface circuit (12) outputs the clock signal CL and the control data D0 to D0.
D7 is output as a clock signal SCL and control data SDI, respectively. The shift register (13) is a cascade connection of eight D-type flip-flops, and shifts 8-bit control data D0 to D7 sequentially to the right in synchronization with the clock signal SCL. The instruction decoder (14)
3 bits D5 to D7 of control data corresponding to the instruction code
Outputs a latch clock signal LCK when it is detected that is a unique value predetermined in the liquid crystal driving integrated circuit (1). Latch circuits (15) (16) (17) (1
8) The other four bits D0 to D3 of the control data for defining the control signals CA0 to CA10 are latched by the latch clock signal L
It latches in synchronization with CK. Similarly, the latch circuit (24) latches one bit D4 of the control data in synchronization with the latch clock signal LCK. The output signal L4 from the Q terminal of the latch circuit (24) is supplied to the transmission gates TG11, TG12 and the operational amplifier (8). That is, when the control data D4 has the logical value "0", the transmission gate TG11 is turned on, the transmission gate TG12 is turned off, and the operational amplifier (8) stops operating. Thus, the liquid crystal driving voltage V
LCD0 to VLCD3 are fixed at the power supply voltage VLCD,
The display contrast of the liquid crystal panel can be fixed or adjusted by external resistance. On the other hand, when the control data D4 has the logical value "1", the transmission gate TG11 is turned off, the transmission gate TG12 is turned on, and the operational amplifier (8) operates. From this, the liquid crystal drive voltage VLC
D0 to VLCD3 are varied in the range of voltages V0 to V10 according to control signals CA0 to CA10, and the display contrast of the liquid crystal panel can be adjusted. The decoder (19) comprises a latch circuit (15)
(16) The output signal from the Q terminal of (17) and (18) and the output signal are converted into inverters (20), (21) and (22).
Based on a total of eight inverted output signals inverted in (23),
Control signals CA0-C in which only one of them becomes high level
A10 is output. Specifically, the decoder (1
9) has 11 AND gates, and the control signal CA in which only one of the 11 AND gates becomes high level
The eight signals are matrix-wired to eleven AND gate inputs inside the decoder (19) so that 0 to CA10 can be output. FIG. 3 shows control data D0 to D3,
FIG. 4 is a diagram illustrating a relationship between control signals CA0 to CA10 and a reference voltage VLCD0. That is, when the control data D0 to D3 have the values shown in FIG. 3, any one of the control signals CA0 to CA10 becomes high level, and the reference voltage VLCD0 is set to any one of V0 to V10. From the above, the value of the reference voltage VLCD0 for liquid crystal display can be changed to 1 by simply changing the control data D0 to D3 to the value specified by the user.
It can be set in one stage (voltages V0 to V10). That is, the display contrast can be adjusted without providing any external components in the liquid crystal drive integrated circuit (1). Therefore, it is possible to reduce the price of an electronic device using the liquid crystal driving integrated circuit (1). Since the serial output port of the external controller is used, it is not necessary to occupy a specific port. Therefore, as the specific port of the external controller can be used for other purposes, the electronic device using the liquid crystal driving integrated circuit (1) can be enhanced in function. The user can adjust the display contrast with an external resistor only when it is determined that the set intervals of the reference voltages V0 to V10 for adjusting the display contrast are not appropriate.
The range of voltage selection for adjusting the display contrast by the user is widened. The operation and effect described above are achieved. In the embodiment of the present invention, the series resistance R
Although 1 is divided into four and the series resistors R5, R6, and R7 are divided into 11, the number of divisions other than this may be selected. According to the present invention, the value of the reference voltage for the liquid crystal display can be set in a plurality of steps simply by changing the control data to the value specified by the user. That is, the display contrast can be adjusted without providing any external components in the liquid crystal drive integrated circuit.
Therefore, it is possible to reduce the price of an electronic device using the liquid crystal driving integrated circuit. Further, since the serial output port of the external controller is used, it is not necessary to occupy a specific port. Therefore, as the specific port of the external controller can be used for another purpose, the electronic device using the liquid crystal driving integrated circuit can be enhanced in function. Further, the display contrast can be adjusted by the external resistor only when the user determines that the setting interval of the reference voltage for adjusting the display contrast obtained from the plurality of second series resistors is inappropriate. There is an advantage that the range of choices is expanded and versatility is expanded.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing a liquid crystal driving integrated circuit of the present invention. FIG. 2 is a circuit diagram showing a part of a liquid crystal driving integrated circuit that outputs a control signal. FIG. 3 is a relationship diagram showing a relationship among control data, a control signal, and a reference voltage. FIG. 4 is a time chart of an external input signal. FIG. 5 is a circuit block diagram showing a conventional liquid crystal driving integrated circuit. FIG. 6 is another circuit block diagram showing a conventional liquid crystal driving integrated circuit. [Description of Signs] (1) Liquid crystal drive integrated circuit (8) Operational amplifier (24) Latch circuit R1 First series resistor R5, R6, R7 Second series resistor TG11, TG12 Transmission gate

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-127618 (JP, A) JP-A-4-237091 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G09G 3/00-3/38 G02F 1/133

Claims (1)

(57) An integrated circuit for generating a liquid crystal driving voltage for driving a liquid crystal panel from each connection point of a plurality of first series resistors, wherein the plurality of first series resistors are connected to each other. In a liquid crystal driving integrated circuit for adjusting a display contrast of the liquid crystal panel by varying a reference voltage applied to one end of a series resistor, a plurality of second series resistors connected to a power supply; A reference voltage generation circuit for generating the reference voltage based on an output of the selection circuit, including a selection circuit for deriving any one of the connection point voltages, and one ends of the plurality of first series resistors connected to a power supply Or cut off
A first switch circuit, a second switch circuit for connecting or disconnecting the plurality of second series resistors to or from a power supply, and a circuit for permitting or stopping the operation of the reference voltage generation circuit. When operating, the first switch circuit is turned off and the second switch circuit is turned on, and when the reference voltage generation circuit is turned off, the first switch circuit is turned on and the second switch circuit is turned off. A liquid crystal driving integrated circuit characterized by the following.