KR100701084B1 - Common voltage modulation circuit for LCD - Google Patents

Abstract

The present invention relates to a common voltage modulation circuit for a liquid crystal display, and more particularly to a circuit for modulating a common voltage used in a liquid crystal display using an OSD (On Screen Display) menu.

The common voltage modulation circuit for a liquid crystal display according to the present invention includes a scaler for generating a pulse wave, a duty ratio adjusting unit for adjusting a duty ratio of the pulse, and converting a pulse output from the duty ratio adjusting unit into a DC voltage. A RC circuit, a controller configured to receive and modulate the DC voltage output from an output terminal of the RC circuit, and receive an output signal of the controller to a non-inverting terminal and output a common voltage through an output terminal connected to an inverting terminal.

In the case of using the circuit of the present invention, the flicker level can be adjusted by finely adjusting the variable width of the common voltage to 10 mV to 20 mV.

Description

Common voltage modulation circuit for liquid crystal display

1 is a circuit diagram of a conventional common voltage generator

2 and 3 illustrate PWM pulse generation.

4 is a common voltage modulation circuit diagram in accordance with the present invention.

The present invention relates to a common voltage modulation circuit for a liquid crystal display, and more particularly to a circuit for modulating a common voltage used in a liquid crystal display using an OSD (On Screen Display) menu.

In general, the common voltage Vcom used in the liquid crystal display device refers to a variable voltage used to cancel a flicker generated on the screen due to a gate line delay.

1 shows a circuit diagram of a conventional common voltage generator.

In FIG. 1, the scaler 10 and the duty ratio controller 11 are coupled to a general purpose input output (GPIO) inside the scaler, and the voltage VcomCT of the node a is a non-inverting terminal of the amplifier 12. Node b represents a terminal for outputting a common voltage Vcom.

The duty ratio of the pulse signal output from the scaler is adjusted by the duty ratio adjusting unit 11. Here, the scaler converts the analog data (R, G, B) generated from the PC into the digital through the ADC block, and in the PLL block inside the scaler, the input frequency obtained by receiving the horizontal signal Hsync is calculated by the internal scaler algorithm. Next, frequency and data and signals are sent to the timing controller (T-com) block to be displayed on the screen.

A general method of duty ratio adjustment is shown in FIGS. 2 and 3.

That is, as is well known, as shown in FIG. 2, a PWM waveform is generated by comparing the sawtooth wave output from the sawtooth generator 20 with a reference DC voltage, or as shown in FIG. 3, the PWM waveform generated in FIG. By adjusting the common voltage variable range (82% ~ 100%) by firmware, adjust the common voltage level (see Table 1-1, 1-2).

TABLE 1-1

Before change after change comment R502 174 174 Resistance unit (Ohms) R503 357 866 Resistance unit (Ohms) Duty ratio (actual value) 81% 81% Duty range 100% 100% Duty range Av (calculated value) 1.49 1.20 Amplification factor (V) VCOMCT (actual value) 1.936 1.936 at least 3.25 3.25 maximum VCOM (Calculated Value) 2.88 2.32 at least 4.83 3.90 maximum VCOM (actual value) 2.898 2.333 at least 4.88 3.92 maximum VCOM_range (actual value) 1.982 1.587 VCOM OSD Range 32 32 Step size = 2 V / step (mV) 61.94 49.59 VCOM OSD 1 Step Voltage

Table 1-2

VCOM Menu Step V / step V / diff Duty / Step Duty / diff 0 0x40 3.19 81.25 0 0x40 3.245 0.055 82.49 1.24 2 0x41 3.3 0.055 83.75 1.26 4 0x42 3.353 0.053 85.00 1.25 6 0x43 3.4 0.047 86.24 1.24 8 0x44 3.45 0.050 87.50 1.26 10 0x45 3.5 0.050 88.74 1.24 12 0x46 3.54 0.040 89.99 1.25 14 0x47 3.59 0.050 91.25 1.26 16 0x48 3.64 0.050 92.49 1.24 18 0x49 3.69 0.050 93.75 1.26 20 0x4A 3.74 0.050 95.00 1.25 22 0x4B 3.79 0.050 96.25 1.25 24 0x4C 3.85 0.060 97.50 1.25 26 0x4D 3.9 0.050 98.76 1.26 28 0x4E 3.94 0.040 100.00 1.24 31 0x4F 3.94 0 100.00 0

In Table 1-2, V / step means common voltage step, and V / diff indicates difference of common voltage step (e.g., 3.245-3.15 = 0.05). Also, the duty / step represents the step of the duty ratio at 81.25% to 100%, and the duty / diff represents the difference of the step of the duty ratio.

In relation to the operation of FIG. 1, the PWM pulse generated by the operation principle as shown in FIGS. 2 and 3 is converted into a DC voltage through the resistance component R501 and the capacitor C501. In FIG. 1, the voltage before amplification is represented by VCOMCT, and the voltage after amplification is represented by VCOM.

Here, VCOM = VCOMCT (1 + R502 / R503). As can be seen from Table 1-1, when the value of the resistance component (R502) is left at 174Ω and the value of the resistance component (R503) is changed from 357Ω to 866Ω, the amplification factor is lowered from 1.49V to 1.20V. have.

The reason for this is that the VCOM variable interval is so large that the amplification factor is lowered. As can be seen from Table 1-1, the V / step becomes smaller from 61.94 to 49.59. Here, V / step means a common voltage step.

However, despite these results, there is a problem that it is difficult to match the flicker level with a V / step of about 49.59. Moreover, unlike the above calculation, the actual measurement has a constant voltage difference as shown in V / diff of Table 1-2. It can be seen.

Therefore, there is a problem that it is difficult to match the flicker level with the conventional common voltage modulation circuit.

The present invention has been proposed to solve the above-described problem, and to provide a common voltage modulation device in which a variable width of a common voltage is reduced to match a flicker level.

The common voltage modulation circuit for a liquid crystal display according to the present invention receives a sawtooth wave generated by the sawtooth generator 20 and a DC voltage 21 that can be adjusted by firmware, and generates a PWM pulse through the comparator 22. An RC circuit for converting a pulse output from a duty ratio adjusting unit for adjusting a duty ratio of a PWM pulse into a DC voltage, a controller for receiving a voltage drop by receiving the DC voltage output from an output terminal of the RC circuit; An amplifier for receiving the output signal to the non-inverting terminal and outputs a common voltage through the output terminal connected to the inverting terminal.

The common voltage modulation circuit for a liquid crystal display according to the present invention includes a comparator 22 for generating a pulse wave, a duty ratio adjusting unit for adjusting a duty ratio of the pulse, and a pulse output from the duty ratio adjusting unit. A RC circuit for converting the circuit into a second circuit; a controller configured to receive the DC voltage outputted from the output terminal of the RC circuit; and a voltage drop; Output

The control unit may include a first resistor connected to one end of the RC circuit unit and a second resistor connected to a non-inverting terminal of the amplifier, a second resistor connected between a power supply voltage and a non-inverting terminal of the amplifier, and And a third resistor coupled between the non-inverting terminal and ground.

(Example)

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Fig. 2 generates a PWM pulse used in the common voltage modulation circuit for the liquid crystal display device according to the present invention, and is composed of a sawtooth wave generator 20, a DC voltage 21, and a comparator 22. The scaler 40 may adjust the flicker level by changing the common voltage using a PWM pulse.

The PWM pulse is input to the non-inverting terminal and the inverting terminal of the comparator 22 and the triangular wave from the sawtooth generator and the DC voltage that can be adjusted by firmware are compared with the sawtooth wave and the DC voltage, respectively. Assuming that 5V and a smaller voltage of 0V are assumed, a PWM pulse is generated. With the PWM pulses generated in this way, the common voltage can be changed in software through the scaler's GPIO port.

4 is a common voltage modulation circuit for a liquid crystal display according to the present invention, and includes a scaler 40, a duty ratio adjusting unit 41, a control unit 43, and an amplifier 42.

The duty ratio of the pulse signal output from the scaler 40 is adjusted by the duty ratio adjusting unit 41. Here, the scaler converts the analog data (R, G, B) generated from the PC into the digital through the ADC block, and in the PLL block inside the scaler, the input frequency obtained by receiving the horizontal signal Hsync is calculated by the internal scaler algorithm. Next, frequency and data and signals are sent to the timing controller (T-com) block to be displayed on the screen.

The output terminal of the duty ratio adjusting unit 41 is connected to a resistance component R18 having a resistance value of 18 KΩ, and a capacitor C43 of 1 ㎌ is connected between the other terminal of the resistance component R18 and ground.

The input terminal of the control unit 43 is connected to the other terminal of the resistance component R18, and the input terminal voltage is represented by VBR (= VCOMCT). The control unit is composed of resistance components R1, R2, and R3, and the resistance components R1 and R3 are connected in series between the power supply voltage VCC = 9.2V and ground, and the intermediate node of the amplifier 42 It is connected to the inverting terminal. In addition, the resistance component R2 is connected to the input terminal of the controller and the non-inverting terminal of the amplifier 42.

The output terminal of the amplifier 42 is connected to the inverting terminal of the amplifier, as shown.

In connection with the circuit of Fig. 4, the current flowing through the resistive component R1, resistive component R2, and resistive component R3 is as follows.

1. The current IR1 flowing through the resistance component R1 is

2. Current (IR2) flowing through resistance component (R2)

3. Current (IR3) flowing through the resistance component (R3)

to be.

Therefore, the voltage drop in the resistance component R1 is R1 * IR1, the voltage drop in the resistance component R2 is R2 * IR2, and the voltage drop in the resistance component R3 is R3 * IR3.

As can be seen in FIG. 4, it can be seen that the moon, in contrast to the prior art, bypasses the VCOMCT voltage in the amplifier and bypasses the VCOMCT voltage to obtain a voltage suitable for the flicker level.

Experimental data relating to the circuit of FIG. 4 is shown in Table 3.

Table 2 below shows the experimental results in consideration of the VBR deviation and the resistance error.

TABLE 2

division Resistance electric current Voltage division Resistance electric current Voltage R1 110000 4.786E05 5.265 R1 110000 4.544E05 4.999 R2 100000 -1.374E05 -1.374 R2 100000 -8.814E05 -0.881 R3 110000 3.577E05 3.395 R3 110000 3.819E05 4.201 VBR 2.726 VBR 3.48 VCC 9.20 VCC 9.20 R1 + R2 8.364E05 9.200 R1 + R2 8.364E05 9.200

When the numerical values of Table 2 are used in the circuit of FIG. 4, it can be seen from Table 3 that the V / step (mV) is between 10 mV and 20 mV.

TABLE 3

VCOMCT / step V / diff (1) VCOM / Step V / diff (2) 1.936 3.655 1.991 0.055 3.674 0.019 2.046 0.055 3.694 0.020 2.099 0.053 3.713 0.019 2.146 0.047 3.729 0.016 2.196 0.050 3.747 0.018 2.246 0.050 3.765 0.018 2.286 0.040 3.779 0.014 2.336 0.050 3.797 0.018 2.386 0.050 3.814 0.017 2.436 0.050 3.832 0.018 2.486 0.050 3.85 0.018 2.536 0.050 3.868 0.018 2.596 0.060 3.889 0.021 2.646 0.050 3.907 0.018 2.686 0.040 3.921 0.014 2.726 0.040 3.935 0.014

In Table 3, V / diff (1) represents the voltage difference between VCOMCT / steps, and V / diff (2) represents the voltage difference between VCOM / steps.

The common voltage modulator of the present invention shown in FIG. 4 can be applied to an LCD monitor, an LCD TV, a digital CNS, and the like having a remote controller using a remote controller. Therefore, the user can easily adjust the common voltage to adjust the flicker level while viewing the OSD menu using the remote controller.

As can be seen from the above, in the conventional case, when the common voltage is applied by software, the variable voltage of the common voltage is too large to be 40 mV to 60 mV, so that the best flicker level cannot be achieved. By adjusting the variable width of the common voltage to 10 mV to 20 mV, the flicker level can be adjusted.

Claims (3)

In the common voltage modulation circuit for liquid crystal display device, From the duty ratio adjusting unit for receiving the sawtooth wave generated by the sawtooth wave generator 20 and the DC voltage 21 that can be adjusted by the firmware as an input to generate a PWM pulse through the comparator 22 and adjust the duty ratio of the PWM pulse RC circuit for converting the output pulse into DC voltage, A control unit which receives the DC voltage output from the output terminal of the RC circuit and drops the voltage; And an amplifier receiving the output signal of the controller to a non-inverting terminal and outputting a common voltage through an output terminal connected to the inverting terminal. In a common voltage modulation circuit for a liquid crystal display device, A comparator for generating a pulse wave, A duty ratio controller for adjusting a duty ratio of the pulse; An RC circuit for converting a pulse output from the duty ratio controller into a DC voltage; A control unit which receives the DC voltage output from the output terminal of the RC circuit and drops the voltage; And an amplifier receiving the output signal of the controller to a non-inverting terminal and outputting a common voltage through an output terminal connected to the inverting terminal. According to claim 1 or claim 2, wherein the control unit is connected between the output terminal of the RC circuit and one end and the first resistor connected to the other terminal of the non-inverting terminal of the amplifier, between the power supply voltage and the non-inverting terminal of the amplifier And a second resistor connected between the non-inverting terminal of the amplifier and the ground, thereby dropping the voltage of the output signal of the RC circuit unit and applying the voltage to the non-inverting terminal of the amplifier. Common voltage modulation circuit.

Images