BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an abbreviated diagram of a gamma voltage output circuit according to an exemplary embodiment of the present invention, which includes a switching circuit, a first resistors string, a second resistors string.
FIG. 2 is a abbreviated diagram of the switching circuit of the gamma voltage output circuit of FIG. 1.
FIG. 3 is an abbreviated diagram showing the parallel connection between the first resistors string and the second resistors string of the gamma voltage output circuit of FIG. 1.
FIG. 4 is an abbreviated equivalent circuitry of the parallel connection between the first resistors string and the second resistors string of the gamma voltage output circuit of FIG. 3.
FIG. 5 is a diagram showing the transmittance of the liquid crystal versus the applied driving voltage.
FIG. 6 is a diagram showing the transmittance of the liquid crystal versus the gray level.
FIG. 7 is a schematic diagram, showing a conventional gamma voltage output circuit.
FIG. 8 is a diagram, showing three gamma curves of transmittance of the liquid crystals versus the gray level, having gamma values of 1.0, 2.0, 3.0.
FIG. 9 is a schematic diagram, showing an another conventional gamma voltage output circuit.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Reference will now be made to the drawings to describe preferred and exemplary embodiments in detail.
Referring to FIG. 1, a gamma voltage output circuit of a liquid crystal display according to an embodiment of the present invention is shown. The liquid crystal display includes a printed circuit board (not shown), which has a driving IC (not shown) and a gamma voltage output circuit 3. The gamma voltage output circuit 3 includes a first resistor string 31, a second resistor string 32, a third resistor string 33 and a fourth resistor string 34, respectively connecting in series between the power source AVDD and ground, and a plurality of switching circuits 35. The first resistor string 31 is disposed in the driving IC, named as internal resistor strings, which includes sixty-five resistors R′0˜R′64 and sixty-four nodes, the sixty-four nodes corresponding to sixty-four gamma voltages V′1˜V′64. The second, third and fourth resistor strings 32, 33, 34 and the plurality of switching circuits 35 are formed out of the driving IC, named as external resistor string. The second resistor string 32 includes fifteen resistors R′0_1˜R′14_1 and fourteen nodes; the third resistor string 33 includes fifteen resistors R′0_2˜R′14_2 and fourteen nodes; and the fourth resistor string 34 includes fifteen resistors R′0_3˜R′14_3 and fourteen nodes. The number of the plurality of switching circuit 35 is fourteen.
The circuit configuration of each switching circuit 35 is shown in FIG. 2, which has an enabling signal input end (EN) 350, a first controlling signal input end (A0) 351, a second controlling signal input end (A1) 352, a first input end (S1) 353, a second input end (S2) 354, a third input end (S3) 353, and an output end (OUT) 356. The switching circuit 35 in the embodiment employs analog switch AD7502. The first input ends (S1) 353 of the fourteen switching circuits 35 respectively electrically connect with the fourteen nodes of the second resistor string 32. The second input ends (S2) 354 of the fourteen switching circuits 35 respectively electrically connect with the fourteen nodes of the third resistor string 33. The third input ends (S3) 355 of the fourteen switching circuits 35 respectively electrically connect with the fourteen nodes of the fourth resistor string 34. The output ends (OUT) 356 of the fourteen switching circuits 35 respectively electrically connect with fourteen nodes of the sixty-four nodes of the first resistor string 31. For different gamma voltage output circuits, the fourteen nodes can be chosen according to different needs. But, for a certain gamma voltage output circuit, the fourteen nodes are changeless.
In operation, when the driving IC sends a high level signal to the enabling signal input end (EN) 350 of the switching circuit 35, the switching circuit 35 starts to work. When the first and the second controlling signal input ends (A0, A1) 351, 352 respectively receive a low level signal, the first input end (S1) 353 electrically connects with the output end (OUT) 356. That is, the resistors of the first resistor string 31 parallel connect to the corresponding resistor of the second resistors string 32. The corresponding resistor of the second resistors string 32 can be chosen according to different needs. FIG. 3 provides one parallel connecting circuitry 41. In FIG. 3, the resistor R′0 parallel connects to the resistor R′0_1; the resistor R′1 parallel connects to the resistor R′1_1; the resistor R′2 parallel connects to the resistor R′2_1; the resistor R′63 parallel connects to the resistor R′13_1; the resistor R′34 parallel connects to the resistor R′14_1. In addition, each six continuous resistors of resistor R′3˜R′62 parallel connect to one resistor of R′3_1˜R′12_1, such as resistors R′(3+6n)˜R′(8+6n) (0≦n≦9) parallel connect to R′(3+n)_1. The sixty-four nodes of the first resistor string 31 respectively output gamma voltages V″1˜V″64.
FIG. 4 shows the equivalent scheme 51 of the parallel circuitry 41 of FIG. 3, the equivalent scheme 51 has sixty-five equivalent resistance R″0˜R″64 and sixty-four nodes. Each node output one gamma voltage. A serial voltages V″1˜V″64 of the equivalent scheme 51 correspond to one gamma curve.
When the driving IC sends a high level signal to the enabling signal input end (EN) 350 of the switching circuit 35, and the first and the second controlling signal input ends (A0, A1) 351, 352 of the switching circuit 35 respectively receive a high level signal and a low level signal, the second input end (S2) 354 electrically connects with the output end (OUT) 356. That is, the resistors of the first resistor string 31 parallel connect to the corresponding resistor of the third resistors string 33, similar to the second resistors string 32. when the driving IC sends a high level signal to the enabling signal input end (EN) 350 of the switching circuit 35, and the first and the second controlling signal input ends (A0, A1) 351, 352 of the switching circuit 35 respectively receive a low level signal and a high level signal, the second input end (S3) 355 electrically connects with the output end (OUT) 356. That is, the resistors of the first resistor string 31 parallel connect to the corresponding resistor of the fourth resistors string 34, similar to the second resistors string 32. When the driving IC sends a low level signal to the enabling signal input end (EN) 350 of the switching circuit 35, the switching circuit 35 turns off.
In the gamma voltage output circuit 3, the numbers of the second, third, fourth resistors strings 32, 33, 34 can also be others. And, the number of the plurality of switching circuits 35 can be determined according to the numbers of the second, third, fourth resistors strings 32, 33, 34.
Comparing to prior arts, the gamma voltage output circuit 3 does not need change the internal circuit configuration of the driving IC, which just add a quantity of resistors at an external peripheral region of the driving IC to realize gamma voltages adjusting according to different needs. Thus, a good displaying characteristics can be attained even in different external environments.
When the LCD needs to be operated in more different external environments, the number of the external resistors string needs to be added. However, the internal circuitry configuration does not need to be changed.
When the driving IC of the LCD is eight bit or ten bit, the number of the internal resistors string is two hundred fifty-six or one thousand twenty-four. However, the number of each external resistors string does not need to be changed or just change a small quantities, such as add to twenty or thirty.
It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.
Patent Application
20080049008
