JPH03155523A - Common driver circuit - Google Patents

Abstract

PURPOSE:To supply common output to which a stable bias is supplied by holding a preset common bias by using the detection output of DC level of an output circuit. CONSTITUTION:A control part 12 connected to a buffer amplifier 11 supplies a preset value set at an amplitude variable volume 13 to the buffer amplifier 11, and also, compares the bias set at a bias variable volume 14 wit a DC level fed back from an output circuit side with a comparator, and varies the bias with comparison output, and supplies it to the buffer amplifier 11. The output of an operational amplifier 15 connected to the buffer amplifier 11 is connected to transistors Q1, Q2 for buffer so as to sufficiently drive a load with heavy capacitance, and is voltage-fed back from its output point a to a (-) input terminal. Meanwhile, the output of a low-pass filter 16 consisting of a resistor R1 and a capacitor C1 is supplied to the control part 12 via a feedback circuit 17. Thereby, the fluctuation of a DC component applying an adverse effect to signal processing is suppressed, which improves reliability.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a common driver circuit for driving a heavy capacitive load such as a common electrode of a liquid crystal panel.

Conventional technique As shown in Figure 6, the common driver circuit incorporated in a conventional new type of liquid crystal display device biases the buffer amplifier (1) to which the common amplitude signal (frame pulse XFP) is input using a variable resistor (2). The amplitude of the common amplitude signal was adjusted by applying this bias and adjusting this bias. Then, the DC component of the output of the buffer amplifier (1) is removed by a DC cut capacitor (C), and a common bias is newly applied by a variable resistor (3). A common bias is applied to the common electrode of the liquid crystal panel by the common amplitude signal (FP) and the variable resistor (3).

Problems to be Solved by the Invention By the way, as mentioned above, in the conventional example, in order to obtain an amplitude signal to which a common bias is applied, the DC component of the output from the buffer amplifier must be cut with a capacitor (Cυ). Therefore, a large capacitor (C1) was required to switch the common for each field.In addition, a common bias was applied to the power supply voltages Vcc and -Vee applied to the variable resistor (3). Therefore, if these power supply voltages fluctuate, the common bias will also fluctuate, which will have an adverse effect on the liquid crystal panel.

As shown in Figure 2, the conventional common output method was to amplify the frame pulse, cut the DC component with (C1), and then apply bias again by resistor division, but the amplitude of the common output is limited to a maximum of 8 vpp. Also, depending on the bias applied, it may not be possible to adjust the voltage that is connected to the bias adjustment (VR) in step 3 with the same voltage as the panel's source power supply voltage.
For this reason, it was necessary to take -Vee from an even lower voltage (-21V). This voltage fluctuates independently of fluctuations in the panel's source power supply voltage, so if the power supply is not stable, direct current may be applied to the panel. If the voltage that determines this bias can be taken from the same power supply line as the panel's source power supply voltage, even if the source power supply voltage fluctuates, the bias set in step 3 will also fluctuate in the same direction according to the fluctuation, so the panel had the disadvantage that it was difficult to apply direct current. In addition, in terms of panel specifications, it was necessary to suppress both fluctuations in the center voltage of the video signal applied to the source driver and fluctuations in the center voltage of the common, even under conditions such as signal content and power supply fluctuations. The video signal has already undergone feedback and is stable, but the common specifications have not always been adhered to for the reasons mentioned above.

The present invention has been devised in view of these points, and eliminates the need for a large-capacity DC cut capacitor without causing fluctuations in the common bias. The object of the present invention is to provide a common driver circuit that can supply a common output with a stable bias.

Means for Solving the Problems In order to achieve the above object, the present invention provides a common driver circuit for driving a liquid crystal panel, which includes an output circuit consisting of a buffer amplifier or a voltage follower capable of sufficiently driving a capacitive load, and the output circuit. means for supplying a common signal and a common bias to a common bias; bias setting means for setting the common bias; detecting a DC level of the output circuit and using the detection output to always maintain the common bias set by the bias setting means; and control means for maintaining the position.

According to such a configuration, the common bias from the bias setting means is applied to the output circuit, and if the common bias fluctuates, the fluctuation is compensated for by the control means so that it is always kept constant. become.

FIG. 1 is a block diagram showing the overall configuration of a liquid crystal display device incorporating a common driver circuit, FIG. 2 is a block diagram of a common driver circuit shown as an embodiment of the present invention, and FIG. FIG. 2 is a circuit diagram showing a specific circuit configuration of each block, and FIG. 4 is a signal waveform diagram of signals in each part of FIGS. 1 and 3.

In the liquid crystal display device shown in Fig. 1, a TFT array (thin
The LCD panel 40 includes a gate driver 40a, a source driver 40b1, and a common driver 39, and a gate driver drive signal is sent from the liquid crystal panel controller 38 to the gate driver 40a, and the source driver 40b is sent to the source driver 40b. The drive signal and the common signal generation signal are respectively input to the common driver 39.

The video signal is transmitted by a sync separation circuit 31 and a Y/C separation circuit 3.
3 is input. The synchronization signal separated in synchronization by the synchronization separation circuit 31 is inputted to the liquid crystal panel controller 38 and the clamp pulse generator 32 in a sine waveform of 10MHz or higher, as shown in FIG. Y/C separation circuit 33
Then, the video signal is separated into a luminance signal and a cross signal, which are input to a video cross signal processing circuit 34. R, G, and B primary color signals are output from the video cross signal processing circuit 34 and input to the brightness, contrast, and gamma correction circuit 35. A clamp pulse from a clamp pulse generator 32 is input to a video cross signal processing circuit 34 and brightness, contrast, and gamma correction 35. The primary color signals R, G, and B from the brightness, contrast, and gamma correction circuit 35 are processed by an inverter circuit 36, and then input from a driver circuit 37 to a source driver circuit 40b as a video signal output. The liquid crystal panel controller 38 inputs the synchronization signal from the synchronization separation circuit 3t and the clock pulse ck, and outputs a gate driver drive signal and a source driver drive signal as panel control signals, and at the same time outputs a frame pulse (synchronized with the signal). FP) or the fourth pulse as an inverted pulse.
A signal for creating a common signal as a horizontal periodic signal of 15 MHz from 0 to 5 (2) as shown in Figure (2) is output. The inverted pulse outputted from the liquid crystal panel controller 38 is manually applied to the inverter 36 and the common driver 39.

15 having a DC level of 0 to 5V as shown in FIG.
The KHz horizontal periodic signal is sent to the terminal shown in Figure 2! 0 to the buffer amplifier 11 as a common amplitude signal.

A control section (12) for controlling bias and amplitude is connected to this buffer amplifier (11). This control section (12) has a variable amplitude volume (I
The set value set in step 3) is given to the buffer amplifier (11), and the bias set by the bias variable volume (14) is compared with the DC level fed back from the output circuit side using a comparator, and the bias is varied based on the comparison output. and provides it to a buffer amplifier (11). Buffer amplifier (11)
The operational amplifier (15) connected to the (+) input terminal has the output from the buffer amplifier (!l) as shown in FIG.
It is supplied as a pulse signal with a DC level of 7V, and the output of the operational amplifier (15) is connected to a buffer transistor (Q
υ(Q,) are connected as shown in the figure, and its output point (
The voltage is fed back from a) to the (=) input terminal. This results in an operational amplifier (15) and a buffer amplifier (Qυ(Q,
) constitutes a voltage follower 18. This voltage follower constitutes an output circuit (18), and the output point (
a) is connected to the common electrode of the liquid crystal panel and is supplied as a pulse signal having a DC level of 1 IV to 17 V with a center bias of 14 as shown in FIG. ) and a capacitor (C1). The output of the low-pass filter (]C6 is supplied to the control section (12) through the feedback circuit (17) as a 14V signal as shown in FIG. The output of the low-pass filter (I6) is applied to the positive input terminal, and 1/2 of the power supply voltage +Vcc is applied to the negative input terminal.
A divided voltage Vcc/2 is applied. The output of the feedback circuit (17) is a 14V signal as shown in FIG. It is coupled to one input terminal of a second comparator (20.degree. 21 in FIG. 3). Note that the other input terminal of this comparator is supplied with a DC voltage set by a variable bias volume (14). The output of this comparator is a pulse signal whose DC level and amplitude are varied by VRs (13) and (14) as shown in FIG.
The bias applied to the buffer amplifier (11) is controlled so that the DC voltage applied from 6) through the feedback circuit (17) and the DC voltage from the bias variable volume (14) match.

The block diagram in FIG. 2 is specifically constructed from the circuit diagram shown in FIG. 3. The buffer amplifier 2 is composed of a differential amplifier 19 and resistors R, , R, , R3, and R4. The voltage follower 18 is composed of an operational amplifier 15 and a pair of buffer transistors Q, , Q. The feedback circuit 17 is composed of a differential amplifier 17 and a resistor R8.

The low-pass filter circuit 16 includes a resistor R7 and a capacitor C1.
Therefore, the DC component is input to the operational amplifier 22 of the feedback circuit 17. The feedback circuit 17 consists of a differential amplifier 22 and a resistor R8, and its output is sent to the first comparator 20. of the control section (12). and second comparator 21
Enter. The control section 12 includes a first comparator 20.
Second comparator 21. Resistance R? , Rs, R@, R
It consists of LO and capacitor C3. 1st comparator 2
A variable amplitude volumetric volume (13) connected to the second comparator 20 is used to adjust the amplitude of the output signal from the control unit (12), and a variable bias volume volume 14 connected to the second comparator 20 is used to adjust the amplitude of the output signal from the control unit (12).
is for adjusting the center bias of the output signal from control 1 (12).

The inverted pulse inputted from the terminal (10) is amplified (or reduced) in the circuit 11 by a control signal from the control section (12), and at the same time, the bias is also controlled. The bias control signal generated by the amplifier circuit (12) is generated by comparing the reference level set by the bias variable volume (14) with the level of the signal generated by the low-pass filter (16) using the feedback circuit (17). , the amplifier (11) is controlled so that the output of the voltage follower (18) is always constant. The capacitor C3 and the resistor R6 are for smoothing.

The inverted pulse inputted to the common driver 39 is set to have a stable amplitude and bias in the specific circuit shown in FIG. 3, and is then applied to the liquid crystal panel LCD.

The common driver circuit according to the present invention consists of a block circuit as shown in FIG. 2, and in addition to the specific circuit shown in FIG. 3, it may be configured as a modified example as shown in the circuit diagram of FIG. 5. In the circuit shown in FIG. 5, an inverted pulse is input to (51) and is input to the operational amplifier (52). The amplitude of the input inverted pulse is adjusted in (53). (5
The output of 2) is input to the voltage follower (54) and taken out as a common output. Also, the common output is R
,7,C,.

It is taken out as a DC output by a low-pass filter consisting of , and is input to a comparator (56).

At (56), the level set at (57) and (58) is compared with the low-pass filter output level, and the comparator output is applied to the voltage follower at (55) through the low-pass filter of Rls and C13. This output is a direct current as shown in FIG. 4, and is added to (52) so that the output of the low-pass filter of R1?1clt is always at the level set at (58). The capacitor CI+ in Figure 5 is for bypassing high frequency components (especially when handling high frequencies). Capacitor CI3 suppresses output bound by smoothing the output of the comparator (56) and lowering it to the reference voltage (output of (57)). Capacitor C1
4 is for protection against noise.

In Figure 5, the common output is smoothed by R+y, C+t (5
6) is input to the comparator. Further, the bias setting VR (58) is taken from the same power supply line as the source power supply voltage of the panel for both Vcc and Vee.

The bias set in (58) not only sets the bias of the common output but also serves as a reference voltage for DC feedback, so that it can also follow fluctuations in the source power supply voltage. When the source power supply voltage fluctuates, it moves in response to fluctuations in the reference voltage, which reduces fluctuations in the voltage applied to the panel.

All circuits are directly connected, so there is no need for a DC cut capacitor. The modified example shown in Fig. 5 not only achieves the same effect as Fig. 4 compared to the one shown in Fig. 4, but also is stable because the feedback resistor (53) is varied with a volume control to adjust the amplitude. .

Effects of the Invention As detailed in the above embodiments, the common driver circuit according to the present invention includes a voltage follower.

It has a simple circuit configuration that includes a low-pass filter, feedback, and control circuits, and improves reliability by suppressing fluctuations in the DC component that adversely affect signal processing in this type of circuit. Furthermore, since the common bias is applied from the front stage of the output circuit, there is no need to cut off direct current, and therefore a large-capacity capacitor for cutting off direct current is not required.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the overall structure of a liquid crystal display device incorporating the common driver circuit of the present invention, FIG. 2 is a block diagram showing the general structure of an embodiment of the common driver circuit according to the present invention, Figure 3 is a circuit diagram showing the detailed circuit configuration of the block diagram in Figure 2, and Figure 4 is a circuit diagram showing the detailed circuit configuration of the block diagram in Figure 1.
Figure 5 is a circuit diagram showing a modification of the circuit diagram in Figure 3; Figure 6 is a circuit diagram showing a modification of the circuit diagram in Figure 3;
The figure is a circuit diagram showing a conventional example of this type of common driver circuit. (1)... Buffer amplifier, (2)... Control section, (3)... Variable amplitude volume, (4)... Variable bias volume, (5)... Operational amplifier, (6)... ...Low pass filter, (7)...Feedback circuit, (8)...Output circuit.

Claims (1)

[Claims] (1) In a common driver circuit for driving a liquid crystal panel, an output circuit consisting of a buffer amplifier or a voltage follower capable of sufficiently driving a capacitive load, and means for supplying a common signal and a common bias to the output circuit;
It consists of a bias setting means for setting the common bias, and a control means for detecting the DC level of the output circuit and using the detected output so that the common bias set by the bias setting means is always maintained. A common driver circuit characterized by: