Patent Application
20050122300
The present application claims priority from Japanese application JP 2003-378595 filed on Nov. 07, 2003 and Japanese application JP 2004-310341 filed on Oct. 26, 2004 the contents of which are hereby incorporated by reference into this application.
1. Field of the Invention
The present invention relates to a semiconductor device and a testing method thereof, and more particularly, it relates to a semiconductor device having a number of external terminals (output terminals) and a testing method for testing output voltage thereof.
2. Description of the Related Art
A semiconductor device provided with a driver circuit of a liquid crystal display (also referred to as a liquid crystal driver circuit, or LCD driver) drives the liquid crystal display (liquid crystal panel) by outputting multi-stage (multiple gray-scale) voltage from a number of external terminals (output pins).
Conventionally, a gray-scale voltage test of a semiconductor device provided with a liquid crystal driver circuit has been done by measuring voltage (e.g., analog voltage measurement) with using a tester. In the present specification, such a tester will be referred to as an Automatic Test Equipment by its abbreviation “ATE”, hereinafter. However, the tester should not be limited to the ATE.
However, with the increase of the number of output terminals in the semiconductor device resulting from the higher definition of the liquid crystal display and with the introduction of higher gray scale in the liquid crystal display in recent years, problems such as extended time required for a gray-scale voltage test and increased cost for testing or manufacturing the semiconductor device (liquid crystal driver circuit) have occurred.
As a method for reducing the time required for the gray-scale voltage test, Japanese Patent Application Laid-Open No. 2002-156412 describes the technique in which differential voltage between output terminal voltage of the liquid crystal driver circuit and reference voltage of an ATE (tester) is detected and then the variances of the gray-scale voltage among the terminals are tested in respective output terminals of the liquid crystal driver circuit.
However, the technique described in Japanese Patent Application Laid-Open No. 2002-156412 has the following problems:
(1) Since output voltage measurement (analog voltage measurement) is performed by the ATE (tester), it takes long until the output voltage is stabilized, and therefore, the testing time is increased.
(2) If the determination range of the output voltage becomes very narrow as a result of the miniaturization of gray-scale voltage steps caused by the introduction of higher gray scale into the liquid crystal display, differential voltage between the output terminal voltage of the liquid crystal driver circuit and reference voltage of the ATE must be subdivided, and therefore, the testing time is increased.
(3) In order to implement the technique described in Japanese Patent Application Laid-Open No. 2002-156412, it is necessary to newly add a gray-scale voltage measuring circuit to the ATE, and thus, the existing (conventional) ATE can no longer be used.
An object of the present invention is to provide the technique capable of solving the problems mentioned above and reducing the time required for the gray-scale voltage test of a semiconductor device provided with a driver circuit of a liquid crystal display. Also, another object thereof is to provide the technique that can reduce the cost of testing/manufacturing a semiconductor device provided with a driver circuit of a liquid crystal display.
The typical ones of the inventions disclosed in this application will be briefly described as follows.
In order to achieve the above-mentioned objects, the semiconductor device having a liquid crystal driver circuit according to the present invention is characterized in that a binarized gray-scale voltage test signal is output when the gray-scale voltage test is carried out.
For instance, the present invention provides a semiconductor device having a liquid crystal driver circuit wherein, in a gray-scale voltage test of the semiconductor device, gray-scale voltage generated in a gray-scale voltage generator circuit of the semiconductor device is compared with reference voltage generated for testing the gray-scale voltage, and the test result is output as binarized voltage from an external terminal of the semiconductor device.
Also, the present invention provides a semiconductor device having a liquid crystal driver circuit wherein the liquid crystal driver circuit comprises: a gray-scale voltage generator circuit; and a gray-scale voltage selector circuit which receives gray-scale voltage generated in the gray-scale voltage generator circuit and selects gray-scale voltage corresponding to gray scale, and in a gray-scale voltage test of the semiconductor device, the gray-scale voltage generated in the gray-scale voltage generator circuit is compared with reference voltage generated for testing the gray-scale voltage in the gray-scale voltage selector circuit, and the test result is output as binarized voltage from an external terminal of the semiconductor device.
Also, the present invention provides a semiconductor device having a liquid crystal driver circuit, wherein the liquid crystal driver circuit comprises: a gray-scale voltage generator circuit; a gray-scale voltage selector circuit which receives gray-scale voltage generated in the gray-scale voltage generator circuit and selects gray-scale voltage corresponding to gray scale; and a buffer which temporarily retains information regarding gray-scale voltage selected in the gray-scale voltage selector circuit and gives the retained information to the gray-scale voltage selector circuit, and the gray-scale voltage selector circuit further comprises: a selector circuit that selects gray-scale voltage generated in the gray-scale voltage generator circuit based on an output from the buffer; an amplifier circuit which, in a gray-scale voltage test of the semiconductor device, compares the gray-scale voltage selected in the selector circuit with reference voltage generated for testing the gray-scale voltage, amplifies differential voltage between those voltages, and outputs the comparison result as binarized voltage from an external terminal; and selection means which selects either the reference voltage or output of the amplifier circuit as information to be input into the amplifier circuit.
Also, the present invention provides a testing method of a semiconductor device having a liquid crystal driver circuit wherein, in a gray-scale voltage test of the semiconductor device, gray-scale voltage generated in a gray-scale voltage generator circuit of the semiconductor device is compared with reference voltage generated for testing the gray-scale voltage, and a test of the gray-scale voltage of the semiconductor device is carried out by using binarized voltage which is output as the test result from an external terminal of the semiconductor device.
Also, the present invention provides a testing method of a semiconductor device having a liquid crystal driver circuit, wherein the liquid crystal driver circuit comprises: a gray-scale voltage generator circuit; and a gray-scale voltage selector circuit which receives gray-scale voltage generated in the gray-scale voltage generator circuit, and the gray-scale voltage generated in the gray-scale voltage generator circuit is compared with reference voltage generated for testing the gray-scale voltage in the gray-scale voltage selector circuit, and the gray-scale voltage of the semiconductor device is tested by using binarized voltage which is output from the semiconductor device as the test result.
Also, the present invention provides a testing method of the semiconductor device wherein, in the gray-scale voltage test, an external terminal of the semiconductor device and a comparator of an ATE (tester) are electrically connected, and the gray-scale test is carried out at once in the comparator of the ATE by using the binarized voltage output from the external terminal.
According to the present invention, it is possible to reduce the time required for the gray-scale voltage test of the semiconductor device provided with a driver circuit of a liquid crystal display (liquid crystal driver circuit).
In addition, it is also possible to reduce the testing/manufacturing cost of the semiconductor device provided with a driver circuit of a liquid crystal display.
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment, and the repetitive description thereof will be omitted.
The gate driver 1 applies a gate signal to the liquid crystal display panel 5. The source driver 2 applies gray-scale output voltage to the liquid crystal display panel 5. The liquid crystal driving voltage generator circuit 3 generates driving voltage for the liquid crystal display panel 5. For example, the liquid crystal display panel 5 has structure in which TFTs are arranged in a matrix and brightness thereof is controlled by charging retention volume of each pixel. The MPU 6 controls operations/processes of the gate driver 1 and the source driver 2.
“The semiconductor device having a driver circuit of a liquid crystal display (liquid crystal driver circuit)” described below in the embodiments of the present invention may be (1) composed of the source driver 2, alternatively (2) composed of the gate driver 1, the source driver 2, and the liquid crystal driving voltage generator circuit 3.
In the case of the semiconductor device having the configuration (2) mentioned above, a unit containing the gate driver 1, the source driver 2, and the liquid crystal driving voltage generator circuit 3 may be referred to as a liquid crystal display controller 4 in some cases. In addition, it is also possible to configure one semiconductor device by adding the MPU 6 to the components described above.
The semiconductor device having the configuration (1) described above is mainly used for driving a large-size liquid crystal display, while the semiconductor device having the configuration (2) is used for driving, for example, a small-size color TFT liquid crystal display provided in a mobile phone.
In
In the following, the semiconductor device having a liquid crystal driver circuit according to the embodiments of the present invention and the testing method thereof will be described with reference to FIGS. 1 to 7.
In
In addition, S1 to Sn shown in
The gray-scale voltage selector circuit 14 includes a plurality of switch circuits 15 that are composed of a selector circuit 18, an amplifier circuit 20, and an operation changeover switch 19.
In addition, the semiconductor device can be configured without the display data RAM 12 if it is not necessary.
In the source driver 2, in normal operation, the test mode changeover circuit 21 controls the operation changeover switch 19 so that the output terminal of the amplifier circuit 20 is connected to the inverting input terminal denoted by the sign “−”. By doing so, the amplifier circuit 20 is placed in the operating state equivalent to the buffer circuit, and the gray-scale voltage selected via the selector circuit 18 is output to the output terminal.
On the one hand, in the source driver 2, during a gray-scale test, the external interface of the display controller (not shown) and an output terminal and a VTEST terminal of the gray-scale voltage selector circuit 14 (switch circuit 15) are connected to the ATE 35, respectively, and the gray-scale test is performed by a test signal from the ATE 35.
More specifically, during the gray-scale test (gray-scale test mode and test mode), the source driver 2 switches the operation changeover switch 19 by the ATE 35 via the test mode changeover circuit 21 so that the VTEST terminal is connected to the inverting input terminal denoted by the sign “−” of the amplifier circuit 20. Then, the source driver 2 compares the gray-scale voltage selected via the selector circuit 18 with the reference voltage applied via the VTEST terminal in the amplifier circuit 20, and outputs the comparison result to the output terminal.
Usually, the amplifier circuit 20 has a high amplification factor. Thus, during the gray-scale test, the amplifier circuit 20 amplifies differential voltage between the gray-scale voltage and the reference voltage, thereby outputting a voltage value in the vicinity of power supply voltage on either the positive side (H) or negative side (L) of the buffer circuit as the output terminal voltage.
Therefore, in the gray-scale test, the output voltage of the source driver 2 becomes any of the predetermined binarized voltages (“H” or “L”) by setting the given gray-scale data from the ATE 35 via the display data RAM 12 and the line buffer circuit 13 and applying the reference voltage onto the VTEST terminal in the ATE 35. Since the output of the gray-scale test signal is binarized voltage, the gray-scale voltage of a plurality of output terminals (output pins) of the source driver 2 can be simultaneously tested in a plurality of comparators CMP1 to CMPn provided in the ATE 35.
In the following, the outline of the operation of the switch circuit 15 shown in
On the one hand, during the gray-scale test of the semiconductor device, the logic state of the test mode changeover circuit 21 is set to “1”. In this manner, the transparent switch composed of the transistors 102a and 102b is in an ON state and the transparent switch composed of the transistors 103a and 103b is in an OFF state. Furthermore, the reference voltage Vcomp supplied from the ATE 35 or the reference voltage generator circuit 22 is applied to the gate of the transistor 101d through the operation changeover switch 19. Consequently, the voltage amplification factor of the amplifier circuit 20 becomes higher when compared with that in the case where the test mode changeover circuit 21 is normally operated, and thus it acts as, so to speak, the amplifier circuit having high amplification factor. Therefore, the amplifier circuit 20 amplifies the difference (differential voltage) between the gray-scale voltage selected by the selector circuit 18 and the reference voltage Vcomp with the voltage amplification factor mentioned above. When the level of the gray-scale voltage is higher than the reference voltage Vcomp, one Vdd of the power supply voltages of the amplifier circuit 20 or the voltage in the vicinity of the power supply voltages is output from the output terminal Vout thereof. In addition, when the level of the above gray-scale voltage is lower than the reference voltage Vcomp, other Vss of the power supply voltages of the amplifier circuit 20 or the voltage in the vicinity of the power supply voltages is output from the output terminal Vout of the amplifier circuit 20.
In the foregoing, one example of the switch circuit 15 has been described with reference to
Next,
If the source driver 2 is normal in this determination of the output voltage, a potential difference between input terminals of the amplifier circuit 20 is +ΔV, voltage corresponding to “H” is output to the output terminal voltage of the source driver 2, and the ATE 35 compares it with the expected value and makes a determination (S5—output voltage “H”). When the output voltage is “L”, the result to the corresponding output terminal will be FAIL (bad) (S10).
Then, the ATE 35 applies reference voltage having a voltage value of (Vx+ΔV) to the VTEST terminal (S6), and compares the output terminal voltage of the source driver 2 with an expected value and makes a determination (S7).
If the source driver 2 is normal in this determination of the output voltage, a potential difference between the input terminals of the amplifier circuit 20 is −ΔV, the voltage corresponding to “L” is output to the output terminal voltage of the source driver 2, and the ATE 35 compares it with the expected value and makes a determination (S7—output voltage “L”). When the output voltage is “H”, the result to the corresponding output terminal will be FAIL (bad) (S10).
Through the process steps of S3 to S7, by setting the reference voltage to (Vx±ΔV) relative to the gray-scale voltage Vx that the source driver 2 has internally selected, it will be tested whether or not the gray-scale voltage is in the predetermined voltage range. When it is normal, the result to the output terminal will be PASS (good) (S9).
It is obvious that, when a test is further done for another gray-scale voltage value Vx′, the process steps of S3 to S7 is similarly repeated with using the gray-scale voltage value (S8). In addition, for the purposes of illustration, the reference voltage herein is set to (Vx±ΔV). However, it is needless to say that the test can be carried out even by setting a given voltage range.
In addition, a liquid crystal display has the characteristic that the display brightness is increased in a curve along with the increase of the input voltage. And when a relation between the gray-scale voltage Vx and the gray-scale value is set to have the nonlinear characteristic as shown in
In addition,
In addition, by adopting the configuration in which a plurality of reference voltage setting units are arranged in the ATE 35 or the configuration in which a plurality of reference voltage input terminals corresponding to the VTEST terminal are arranged, different reference voltages can be applied to each of a plurality of switch circuits 15. Therefore, the different gray-scale voltage test can be carried out for each switch circuit (each output terminal).
For instance, when (Vx+ΔV) is applied to one group of output terminals and (Vx−Δx) is applied to another group of output terminals, “H” and “L” are mixed in the output from the source driver 2. By applying this, “H” and “L” are alternately output from the output terminals (if they are normal) when (Vx+ΔV) is applied to the output terminals of odd number and (Vx−ΔV) is applied to the output terminals of even number. In this manner, a short among output terminals can be detected, thus improving the reliability of the gray-scale test.
The testing methods and configuration in which reference voltages of different voltage values are applied are also available, for example, (Vx+Δ1) is applied to one group of output terminals, while (Vx+ΔV2) is applied to another group of output terminals, alternatively, (Vx1+ΔV) is applied to one group of output terminals, while (Vx2+ΔV) is applied to another group of output terminals, etc.
In addition, it is obvious that the present invention is not limited to the gray-scale test described above, and the present invention can be used in a functional test of, for example, a liquid crystal display controller by adjusting the combination of the gray-scale setting data and the reference voltages.
Subsequently, as a semiconductor device having a liquid crystal driver circuit in the second embodiment of the present invention, configuration and one example of the operation in the case where a reference voltage generator circuit is arranged within a display controller will be described.
The liquid crystal driver circuit in the semiconductor device of the second embodiment is applied to, for example, the source driver 2 shown in
The liquid crystal display controller 4 including this source driver 2 is composed of a display data RAM 12 that stores data written or read through an external interface, a line buffer circuit 13 that retains data written to the display data RAM 12, a gray-scale voltage generator circuit 16 that generates gray-scale voltage at a predetermined level, a gray-scale voltage selector circuit 14 that outputs gray-scale voltage according to the gray-scale setting data retained in the line buffer circuit 13 based on the predetermined gray-scale voltage generated in the gray-scale voltage generator circuit 16, a test mode changeover circuit 21 that switches the operation mode between normal operation and a gray-scale test, and a reference voltage generator circuit 22 that generates the reference voltage based on the gray-scale voltage generated in the gray-scale voltage generator circuit 16.
The gray-scale voltage selector circuit 14 includes plurality of switch circuits 15 composed of a selector circuit 18, an amplifier circuit 20, and an operation changeover switch 19.
In normal operation, the source driver 2 performs the operations equivalent to those of the source driver in the first embodiment described with reference to
Usually, the amplifier circuit has a high amplification factor. Thus, during the gray-scale test, the amplifier circuit 20 amplifies differential voltage between the gray-scale voltage and the reference voltage, thereby outputting a voltage value in the vicinity of power supply voltages either on the positive side (H) or negative side (L) of the buffer circuit as the output terminal voltage.
In the second embodiment, since the reference voltage in the gray-scale test is generated inside the circuit of the source driver 2, the gray-scale test can be carried out relatively within the circuit, and thus, it is possible to reduce the test time. More specifically, in the second embodiment, the test time can be reduced because the rising edge of the reference voltage generated when reference voltage is applied from outside of the semiconductor device shown in
In addition, in order to improve the precision of the gray-scale voltage test of the source driver 2, though not shown in
Next, the circuit configuration and one example of operation of the reference voltage generator circuit 22 of the semiconductor device in the second embodiment will be described with reference to
The reference voltage generator circuit 22 in the second embodiment is composed of a reference voltage resistor 23 that generates reference voltage for each gray-scale voltage based on the gray-scale voltage generated in the gray-scale voltage generator circuit 16, a plurality of buffer circuits 24 that amplify each divided voltage by the reference voltage resistors 23 with the amplification factor of 1, a plurality of switches 25 that switch the output of the buffer circuit 24 and connect it to the gray-scale voltage selector circuit 14 as reference voltage, and a decoder circuit 26 that controls ON/OFF of a plurality of switches 25 based on gray-scale setting data and reference voltage selection signal.
Data identical to the gray-scale setting data to be set to the gray-scale voltage selector circuit 14 is set as the gray-scale setting data that is the control input of the decoder circuit 26, and as shown in
While we have shown and described several embodiments in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of numerous changes and modifications as known to those skilled in the art, and we therefore do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-378595 | Nov 2003 | JP | national |
| 2004-310341 | Oct 2004 | JP | national |
