# Patent

## Title
Driving apparatus, driving apparatus operating method, and self-judgement slew rate enhancing amplifier

## Abstract

A driving apparatus applied in a liquid crystal display is disclosed. The driving apparatus at least includes a first latch, a second latch, an output buffer, and a slew rate enhancing module. The first latch is used to store a second data signal. The second latch is used to store a first data signal. The first data signal is previous to the second data signal. The slew rate enhancing module is used to compare the first data signal and the second data signal to generate a compared result, and correspondingly output a control signal to the output buffer according to the compared result to control a driving current of the output buffer.

## Background
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a liquid crystal display; in particular, to a driving apparatus, a driving apparatus operating method, and a self-judgment slew rate enhancing amplifier applied in the liquid crystal display.
2. Description of the Related Art
In recent years, with the development of display technology, various novel types of display apparatus having different functions and advantages are shown in the market to replace the conventional cathode ray tube (CRT) monitor. Among them, the liquid crystal display (LCD) having advantages of saving power and small size is very popular and becomes a mainstream of the display market.
In general, the driving circuit in the LCD includes a timing controller (TCON), a source driver, and a gate driver. The timing controller is a control IC used for generating and outputting a control timing to control the timings of the source driver and the gate driver of the LCD panel.
Please refer to FIG. 1. FIG. 1 shows a conventional source driver. As shown in FIG. 1, the source driver 1 includes first latches 10a and 10b, second latches 12a and 12b, level shifters 14a and 14b, a N-type digital-analog converter 16a, a P-type digital-analog converter 16b, an exchanging switch 18, output buffers 19a and 19b, and output pads 20a and 20b. After a timing controller (not shown in FIG. 1) transmits digital input data to the source driver 1, the digital input data will be orderly stored in the first latches 10a and 10b corresponding to the first channel and the second channel respectively. When a STB signal is received, the digital input data will be stored in the second latches 12a and 12b respectively. Then, the digital input data with low level will be converted into the digital input data with high level by the level shifters 14a and 14b respectively, and then converted into analog input data by the N-type digital-analog converter 16a and the P-type digital-analog converter 16b respectively. Then, the exchanging switch 18 will selectively transmit the analog voltage to the output buffer 19a and 19b respectively and output the analog voltage to a display panel (not shown in FIG. 1) through the output pads 20a and 20b respectively to drive pixels on the display panel.
It should be noticed that the slew rate is defined as the rising or the falling of voltage in 1 msec. As to square wave, the conversion time needed for the output voltage to rise from wave trough to wave crest or fall from wave crest to wave trough is determined by the output current and the conversion voltage of the output voltage between the wave crest and wave trough. Every time when the digital input data that the timing controller inputs into the source driver 1 is changed, the analog voltage that the source driver 1 outputs to the display panel will be changed correspondingly. Different output voltage differences will make the output converting time also different. This will result in different voltage converting rates and affect the charging/discharging time of the panel pixels and limit its reaction time, so that the display quality of the display panel will be seriously damaged. Therefore, the above-mentioned problems occurred in the prior arts should be solved.
SUMMARY OF THE INVENTION
Therefore, the invention provides a driving apparatus, a driving apparatus operating method, and a self-judgment slew rate enhancing amplifier applied in the liquid crystal display to solve the above-mentioned problems occurred in the prior arts.
An embodiment of the invention is a driving apparatus. In this embodiment, the driving apparatus is applied to a liquid crystal display. The driving apparatus includes a first latch, a second latch, an output buffer, and a slew rate enhancing module. The first latch is used for storing a second data signal. The second latch is coupled to the first latch and used for storing a first data signal, wherein the first data signal is previous to the second data signal. The slew rate enhancing module is coupled to the first latch, the second latch, and the output buffer respectively and used for comparing the first data signal and the second data signal to generate a compared result and correspondingly output a control signal to the output buffer according to the compared result to control a driving current of the output buffer.
In an embodiment, the slew rate enhancing module includes a comparing unit and a level shifting unit. The comparing unit has two input terminals and an output terminal. The two input terminals are coupled to the first latch and the second latch respectively and receive the second data signal and the first data signal. The comparing unit compares the first data signal and the second data signal to generate the compared result and the output terminal outputs the compared result. The level shifting unit is coupled to the output terminal of the comparing unit and the output buffer. The level shifting unit correspondingly converts the compared result with low level into the control signal with high level and outputs the control signal to the output buffer.
In an embodiment, the comparing unit is a logical judgment circuit.
In an embodiment, the driving apparatus further includes a level shifter and a digital-analog converter. The level shifter is coupled to the second latch and used for converting the first data signal and the second data signal from low level to high level respectively. The digital-analog converter is coupled to the level shifter and used for converting the first data signal and the second data signal from digital voltage to analog voltage respectively.
In an embodiment, the digital-analog converter is an N-type digital-analog converter or a P-type digital-analog converter used for outputting a negative analog voltage or a positive analog voltage.
In an embodiment, the driving apparatus further includes an exchanging switch coupled between the digital-analog converter and the output buffer. The exchanging switch is used for selectively transmitting the negative analog voltage or the positive analog voltage outputted by the digital-analog converter to the output buffer.
Another embodiment of the invention is a driving apparatus operating method. In this embodiment, the driving apparatus operating method is used for operating a driving apparatus applied to a liquid crystal display. The driving apparatus includes a first latch, a second latch, and an output buffer. A first data signal stored in the second latch is previous to a second data signal stored in the first latch. The method includes steps of: (a) comparing the first data signal with the second data signal to generate a compared result; (b) correspondingly output a control signal to the output buffer according to the compared result to dynamically adjust a driving current of the output buffer.
Another embodiment of the invention is a self-judgment slew rate enhancing amplifier. The self-judgment slew rate enhancing amplifier is applied to a driving apparatus of a liquid crystal display. The driving apparatus includes a first latch, a second latch, and an output buffer. The self-judgment slew rate enhancing amplifier includes two input terminals, a comparing unit, and an output terminal. The two input terminals is coupled to the first latch and the second latch respectively and receive the second data signal and the first data signal from the first latch and the second latch respectively. The comparing unit is coupled to the two input terminals and used for comparing the first data signal and the second data signal to generate a compared result. The output terminal is coupled to the comparing unit and used for outputting the compared result.
Compared to the prior art, the driving apparatus of the invention compares the current data and the previous data stored in the first latch and the second latch respectively to generate a compared result, and then correspondingly controls the driving current of the output buffer according to the compared result. With appropriate design, all voltage conversions under different conditions can be adjusted to have the same rate to keep the same slew rate of the source driver to further maintain the display quality of the display panel.
The advantage and spirit of the invention may be understood by the following detailed descriptions together with the appended drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a schematic diagram of the conventional source driver.
FIG. 2 illustrates a function block diagram of the driving apparatus in an embodiment of the invention.
FIG. 3 illustrates an embodiment of the slew rate enhancing circuit.
FIG. 4 illustrates a flow chart of the driving apparatus operating method in another embodiment of the invention.



DETAILED DESCRIPTION
An embodiment of the invention is a driving apparatus. In this embodiment, the driving apparatus can be a source driver applied in a liquid crystal display, but not limited to this. Please refer to FIG. 2. FIG. 2 illustrates a function block diagram of the driving apparatus in this embodiment.
As shown in FIG. 2, the driving apparatus 3 includes first latches 30a and 30b, second latches 32a and 32b, level shifters 34a and 34b, a N-type digital-analog converter 36a, a P-type digital-analog converter 36b, an exchanging switch 38, output buffers 39a and 39b, output pads 40a and 40b, and slew rate enhancing modules E1 and E2. The slew rate enhancing module E1 includes a comparing unit C1 and a level shifting unit LS1; the slew rate enhancing module E2 includes a comparing unit C2 and a level shifting unit LS2. In fact, the comparing units C1 and C2 can be a logical judgment circuit, for example, an exclusive-OR gate (XOR gate) or an inverse of the XOR gate (XNOR gate), but not limited to this.
The first latch 30a, the second latch 32a, the level shifter 34a, and the N-type digital-analog converter 36a are belong to a first channel; the first latch 30b, the second latch 32b, the level shifter 34b, and the P-type digital-analog converter 36b are belong to a second channel. Wherein, the first channel and the second channel are adjacent channels.
The first latch 30a is coupled to the second latch 32a; the second latch 32a is coupled to the level shifter 34a; the level shifter 34a is coupled to the N-type digital-analog converter 36a; the N-type digital-analog converter 36a is coupled to the exchanging switch 38; the exchanging switch 38 is coupled to the output buffers 39a and 39b; the output buffer 39a is coupled to the output pad 40a. The comparing unit C1 of the slew rate enhancing module E1 has two input terminals T1 and T2 and an output terminal T3, wherein the two input terminals T1 and T2 are coupled to the first latch 30a and the second latch 32a respectively, and the output terminal T3 is coupled to the level shifting unit LS1. The level shifting unit LS1 is coupled to the output buffers 39a. 
The first latch 30b is coupled to the second latch 32b; the second latch 32b is coupled to the level shifter 34b; the level shifter 34b is coupled to the P-type digital-analog converter 36b; the P-type digital-analog converter 36b is coupled to the exchanging switch 38; the exchanging switch 38 is coupled to the output buffers 39a and 39b; the output buffer 39b is coupled to the output pad 40b. The comparing unit C2 of the slew rate enhancing module E2 has two input terminals T4 and T5 and an output terminal T6, wherein the two input terminals T4 and T5 are coupled to the first latch 30b and the second latch 32b respectively, and the output terminal T6 is coupled to the level shifting unit LS2. The level shifting unit LS2 is coupled to the output buffers 39b. 
In this embodiment, after a timing controller (not shown in FIG. 1) transmits digital input data to the source driver 3, the digital input data will be orderly stored in the first latches 30a and 30b corresponding to the first channel and the second channel respectively. When a STB signal is received, the digital input data will be stored in the second latches 32a and 32b respectively. Then, the digital input data with low level will be converted into the digital input data with high level by the level shifters 34a and 34b respectively, and then the digital input data (voltage) is converted into analog input data (voltage) by the N-type digital-analog converter 36a and the P-type digital-analog converter 36b respectively. Then, the exchanging switch 38 will selectively transmit the analog voltage to the output buffers 39a or 39b respectively and output the analog voltage to a display panel (not shown in FIG. 2) through the output pads 40a and 40b respectively to drive pixels on the display panel.
It is assumed that the data signals stored in the first latch 30a and the second latch 32a corresponding to the first channel are a first data signal and a second data signal respectively, and the first data signal is previous to the second data signal. That is to say, if the second data signal is a current data signal, the first data signal will be a previous data signal.
It should be noticed that the two input terminals T1 and T2 of the comparing unit C1 of the slew rate enhancing module E1 will receive the first data signal and the second data signal from the first latch 30a and the second latch 32a respectively, and then the comparing unit C1 will compare the first data signal and the second data signal to generate a compared result CR1, and the output terminal T3 will output the compared result CR1 to the level shifting unit LS1. In fact, the comparing unit C1 can do a subtraction on the first data signal and the second data signal to obtain the compared result CR1, but not limited to this.
For example, if the first data signal (previous data signal) stored in the first latch 30a is 0000_0000 and the second data signal (current data signal) stored in the second latch 32b is 1111_0000, the comparing unit C1 can subtract the first data signal (previous data signal) from the second data signal (current data signal) to obtain the compared result CR1 of 1111_0000.
After the level shifting unit LS1 receives the compared result CR1 from the comparing unit C1, the level shifting unit LS1 will correspondingly convert the low-level compared result CR1 into a high-level control signal CS1, and output the control signal CS1 to the output buffer 39a to control the driving current of the output buffers 39a. For example, if the compared result CR1 is 0, it means that the second data signal (current data signal) is equivalent to the first data signal (previous data signal). Therefore, it is unnecessary to adjust the driving current of the output buffer 39a to keep the same slew rate.
Similarly, it is assumed that the data signals stored in the first latch 30b and the second latch 32b corresponding to the second channel are a third data signal and a fourth data signal respectively, and the third data signal is previous to the fourth data signal. That is to say, if the fourth data signal is a current data signal, the third data signal will be a previous data signal. The two input terminals T4 and T5 of the comparing unit C2 of the slew rate enhancing module E2 will receive the third data signal and the fourth data signal from the first latch 30b and the second latch 32b respectively, and then the comparing unit C2 will compare the third data signal and the fourth data signal to generate a compared result CR2, and the output terminal T6 will output the compared result CR2 to the level shifting unit LS2. In fact, the comparing unit C2 can do a subtraction on the third data signal and the fourth data signal to obtain the compared result CR2, but not limited to this. After the level shifting unit LS2 receives the compared result CR2 from the comparing unit C2, the level shifting unit LS2 will correspondingly convert the low-level compared result CR2 into a high-level control signal CS2, and output the control signal CS2 to the output buffer 39b to control the driving current of the output buffers 39b. 
Please refer to FIG. 3. FIG. 3 shows an embodiment of the slew rate enhancing circuit. As shown in FIG. 3, the slew rate enhancing circuit includes P-type transistor switches MP1 ̃MP10, N-type transistor switches MN1 ̃MN10, an output terminal INN and INP, and an output terminal OUT. After the compared voltage signal is inputted into the slew rate enhancing circuit, the slew rate enhancing circuit will correspondingly control the driving current according to the compared voltage signal to increase the slew rate. When the conversion voltage of the output voltage between the wave crest and wave trough is large, the slew rate enhancing circuit can be used to reduce the conversion time needed for the output voltage to rise from wave trough to wave crest or fall from wave crest to wave trough, so that the slew rate can be keep the same without any variation under different conditions.
Another embodiment of the invention is a self-judgment slew rate enhancing amplifier. In this embodiment, the self-judgment slew rate enhancing amplifier is applied to a driving apparatus of a liquid crystal display. The driving apparatus includes a first latch, a second latch, and an output buffer. The self-judgment slew rate enhancing amplifier includes two input terminals, a comparing unit, and an output terminal. The two input terminals is coupled to the first latch and the second latch respectively and receive the second data signal and the first data signal from the first latch and the second latch respectively. The comparing unit is coupled to the two input terminals and used for comparing the first data signal and the second data signal to generate a compared result. The output terminal is coupled to the comparing unit and used for outputting the compared result. Since the self-judgment slew rate enhancing amplifier is disclosed in the above-mentioned embodiments, it is not mentioned again.
Another embodiment of the invention is a driving apparatus operating method. In this embodiment, the driving apparatus operating method is used for operating a driving apparatus applied to a liquid crystal display. The driving apparatus includes a first latch, a second latch, and an output buffer. A first data signal stored in the second latch is previous to a second data signal stored in the first latch. Please refer to FIG. 4. FIG. 4 illustrates a flow chart of the driving apparatus operating method in another embodiment of the invention.
As shown in FIG. 4, in the step S14, the method converts the first data signal from low level to high level. In the step S16, the method converts the first data signal from digital voltage to analog voltage (negative analog voltage or positive analog voltage). In the step S18, the method selectively transmits negative analog voltage or positive analog voltage to the output buffer. In fact, the step S14 will also convert the second data signal from low level to high level. The step S16 will also convert the second data signal from digital voltage to analog voltage (negative analog voltage or positive analog voltage).
In the step S20, the method compares the first data signal and the second data signal to generate a compared result. In the step S22, the method correspondingly outputs a control signal to the output buffer according to the compared result to dynamically adjust a driving current of the output buffer. In fact, the step S22 correspondingly converts the low-level compared result into the high-level compared result and outputs it to the output buffer.
Compared to the prior art, the driving apparatus of the invention compares the current data and the previous data stored in the first latch and the second latch respectively to generate a compared result, and then correspondingly controls the driving current of the output buffer according to the compared result. With appropriate design, all voltage conversions under different conditions can be adjusted to have the same rate to keep the same slew rate of the source driver to further maintain the display quality of the display panel.
With the example and explanations above, the features and spirits of the invention will be hopefully well described. Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teaching of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.

## Claims

1. A self-judgment slew rate enhancing amplifier, applied to a driving apparatus of a liquid crystal display, the driving apparatus comprising a first latch, a second latch, and an output buffer, the self-judgment slew rate enhancing amplifier comprising:
10 P-type transistor switches;
10 N-type transistor switches;
two input terminals, coupled to the first latch and the second latch respectively and
receiving the second data signal and the first data signal from the first latch and the second latch respectively;
a comparing unit, coupled to the two input terminals, for comparing the first data signal and the second data signal to generate a compared result; and
an output terminal, coupled to the comparing unit, for outputting the compared result;
wherein the driving apparatus further comprises a level shifting unit coupling to the output terminal and the output buffer, the level shifting unit correspondingly converts the compared result with low level into the control signal with high level and outputs the control signal to the output buffer according to the compared result to control a driving current of the output buffer to increase a slew rate.

2. The self-judgment slew rate enhancing amplifier of claim 1, wherein the comparing unit is a logical judgment circuit.