Patent Application
20080180418
The present invention relates to liquid crystal panel control circuits, and especially to a liquid crystal panel control circuit having a comparator and a reset circuit, and a liquid crystal display driving circuit including the control circuit.
A typical LCD has the advantages of portability, low power consumption, and low radiation. LCDs have been widely used in various portable information products, such as notebooks, personal digital assistants (PDAs), video cameras and the like. Furthermore, the LCD is considered by many to have the potential to completely replace CRT (cathode ray tube) monitors and televisions. Driving circuits are essential components for driving the LCDs.
Referring to
The system control circuit 19 includes a plurality of data signal output terminals 192 and a direct current voltage output terminal 191. The data signal output terminals 192 are connected to the timing control circuit 16 via a plurality of data signal lines 18. The direct current voltage output terminal 191 is connected to the timing control circuit 16 and the DC-to-DC converting circuit 13 respectively. And the timing control circuit 16 is connected to the DC-to-DC converting circuit 13.
The direct current voltage output terminal 191 outputs a direct current voltage Vc, and the data signal output terminals 192 output pulse voltages Vd. A value of the direct current voltage Vc is equal to a value of the pulse voltages Vd.
The timing control circuit 16 includes a plurality of electro static discharge (ESD) lines 161 in parallel. Each of the ESD lines 161 includes a first diode 162 and a second diode 163 connected in series. Negative electrodes of the first diodes 162 are connected to the direct current voltage output terminal 191 of the system control circuit 19. Positive electrodes of the second diodes 163 are connected to ground. Each of the data signal lines 18 is connected to a positive electrode of a corresponding first diode 162.
The DC-to-DC converting circuit 13 has a protection status. When the DC-to-DC converting circuit 13 receives a direct current voltage less than a direct current working voltage thereof, the DC-to-DC converting circuit 13 comes into the protection status from an initial status. In such a case, even a normal direct current working voltage is provided to the DC-to-DC converting circuit 13, the DC-to-DC converting circuit 13 is still in the protection status, and does not work.
At the instant of starting the an LCD, if the system control circuit 19 outputs direct current voltages to the liquid crystal panel control circuit 10 firstly, the direct current voltage converting circuit 13 can work normally. If the system control circuit 19 outputs data signals to the liquid crystal panel control circuit 10 firstly, the pulse voltage Vd of the data signals is dropped 0.7V by the first diode 162 of the timing control circuit 16. And the dropped pulse voltage Vd is transferred to the DC-to-DC converting circuit 13. Thus the DC-to-DC converting circuit 13 comes into a protection status, and does not work even the direct current voltage Vc is provided to the DC-to-DC converting circuit 13 after a short time. Thus, the DC-to-DC converting circuit 13 can not work normally. Therefore, the liquid crystal panel control circuit 10 can not work normally.
To make sure the direct current voltage is provided firstly, a design of the system control circuit 19 is complicated, and accordingly a cost is increased.
What is needed, therefore, is a liquid crystal panel control circuit that can overcome the above-described deficiencies.
In one preferred embodiment, a liquid crystal panel control circuit includes a direct current converting circuit. The direct current converting circuit includes a comparator, a reset circuit, and a DC-to-DC converting circuit connected in series.
Other novel features and advantages will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.
Reference will now be made to the drawing figures to describe various embodiments of the present invention in detail.
Referring to
The system control circuit 29 is configured for providing data signals for the timing control circuit 26, and providing direct current voltages for the timing control circuit 26 and the direct current converting circuit 23 respectively. The timing control circuit 26 is configured for providing the received data signals to a liquid crystal panel (not shown). The direct current converting circuit 23 is configured for providing the received direct current voltages to integrated circuits (ICs) (not shown) connected thereto.
The system control circuit 29 includes a plurality of data signal output terminals 292 and a direct current voltage output terminal 291. The data signal output terminals 292 are connected to the timing control circuit 26 via a plurality of data signal lines 28. The direct current voltage output terminal 291 is connected to the timing control circuit 26 and the direct current converting circuit 23 respectively. And the timing control circuit 26 is connected to the direct current converting circuit 23.
The direct current voltage output terminal 291 outputs a direct current voltage Vc, and the data signal terminals 292 output pulse voltages Vd. A value of the direct current voltage Vc is equal to a value of the pulse voltages Vd.
The direct current converting circuit 23 includes a DC-to-DC converting circuit 233, a comparator 231, and a reset circuit 232. A first input terminal 235 of the DC-to-DC converting circuit 233 and a second input terminal 236 of the comparator 231 are both connected to the direct current voltage output terminal 291 of the system control circuit 29. An output terminal of the comparator 231 is connected to an input terminal of the reset circuit 232. An output terminal of the reset circuit 232 is connected to a reset control terminal of the DC-to-DC converting circuit 233.
The DC-to-DC converting circuit 233 has a protection status. When the DC-to-DC converting circuit 233 receives a direct current voltage less than a direct current working voltage thereof, the DC-to-DC converting circuit 233 comes into the protection status from an initial status. In such a case, even a normal direct current working voltage is provided to the DC-to-DC converting circuit 233, the DC-to-DC converting circuit 233 is still in the protection status, and does not work normally.
The timing control circuit 26 includes a plurality of electro static discharge (ESD) lines 261 in parallel. Each of the ESD lines 261 includes a first diode 262 and a second diode 263 connected in series. Negative electrodes of the first diodes 262 are connected to the direct current voltage output terminal 291 of the system control circuit 29. Positive electrodes of the second diodes 263 are connected to ground. Each of the data signal lines 28 is connected to a positive electrode of a corresponding first diode 262.
The comparator 231 has a predetermined reference voltage Vr, and the reference voltage Vr satisfies a relationship: Vc-0.7V<Vr<Vc, wherein 0.7V is a voltage drop when the first diodes 262 are turned on. And preferably, the reference voltage Vr is in the range from (Vc-0.5V) to (Vc-0.2V). When the first input terminal 235 of the comparator 231 receives a direct current voltage less than the reference voltage Vr, the comparator 231 outputs a low level voltage to the reset circuit 232. The reset circuit 232 does not work at the low level voltage. When the first input terminal 235 of the comparator 231 receives a direct current voltage greater than the reference voltage Vr, the comparator 231 outputs a high level voltage to the reset circuit 232. In such a case, the reset circuit 232 outputs a high level voltage to the reset control terminal of the DC-to-DC converting circuit 233. Then the DC-to-DC converting circuit 233 is returned to the initial status.
At the instant of starting the LCD, if the system control circuit 29 outputs direct current voltages to the liquid crystal panel control circuit 20 firstly, the direct current voltage converting circuit 23 can work normally. If the system control circuit 29 outputs data signals to the liquid crystal panel control circuit 20 firstly, the pulse voltage Vd of the data signals is dropped 0.7V by the first diode 262 of the timing control circuit 26. The dropped pulse voltage Vd is transferred to the DC-to-DC converting circuit 233. Thus the DC-to-DC converting circuit 233 comes into the protection status, and does not work normally. That is, the DC-to-DC converting circuit 233 can not output desired direct current voltages to the ICs connected thereto.
However, after a short time, when the direct current voltage output terminal 291 starts to output the direct current voltage Vc to the direct current converting circuit 23, the comparator 231 receives the direct current voltage Vc, and then outputs a high level voltage to the reset circuit 232. The reset circuit outputs a high level voltage to the reset control terminal of the DC-to-DC converting circuit 233. Thus, the DC-to-DC converting circuit 233 returns to the initial status. When the second input terminal 236 receives the delayed direct current voltage Vc, the DC-to-DC converting circuit 233 works normally, and outputs desired direct current voltages to the ICs connected thereto.
Because the direct current converting circuit 23 includes the reset circuit 232, when the DC-to-DC converting circuit 233 comes into the protection status at the startup of the LCD, the reset circuit 232 can output a high level voltage for returning the DC-to-DC converting circuit 233 to the initial status. After that, when the delayed direct current voltage is provided to the DC-to-DC converting circuit 233, the DC-to-DC converting circuit 233 can work normally.
Unlike a conventional liquid crystal panel control circuit, the direct current converting circuit 23 can return to the initial status from the protection status by the reset circuit 232. Thus, even data signals are provided firstly, the direct current converting circuit 23 can work normally without restarting an LCD. What is more, when an LCD driving circuit uses the liquid crystal panel control circuit 20, the system control circuit 29 can be designed freely. That is, when the system control circuit 29 is designed, the designer needs not to make sure that the direct current voltage is outputted firstly. Even data signals are provided firstly, the liquid crystal panel control circuit 20 can work normally. Therefore, the design of the system control circuit 29 is simplified. Accordingly, a cost of the LCD driving circuit 2 is reduced.
It is to be understood, however, that even though numerous characteristics and advantages of the present embodiments have been set out in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 200710073125.7 | Jan 2007 | CN | national |
