JP3093685B2 - Integrated circuit and its function test method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an integrated circuit serving as a voltage generating circuit of an LCD (Liquid Crystal Display) and a method for testing its function .

[0002]

2. Description of the Related Art FIG. 3 is a diagram showing a configuration of a conventional voltage generating circuit for generating a voltage to be supplied to a segment driver or a common driver of an LCD. In this figure, resistors 1 to 3 are interposed in series between a power supply VDD and ground, and generate a plurality of reference levels VLC0, VLC1, VLC2 and Vss from each node where each resistor is connected to the other. The unit 10 is constituted.

[0003] Transistors 101 to 112 are connected in a tree shape as shown in the figure, and a voltage output circuit 100 for supplying a segment voltage and a common voltage to the LCD.
Is composed.

More specifically, the sources of the transistors 101 and 105 are connected to the reference level V of the reference power supply 10.
Transistor 1 is commonly connected to a node that generates LC0.
Sources 02 and 106 are commonly connected to a node of the reference power supply 10 that generates a reference level VLC1, and sources of transistors 103 and 107 are commonly connected to a node of the reference power supply 10 that generates a reference level VLC2. Sources 104 and 108 are commonly connected to a node of the reference power supply 10 that generates a reference level Vss.

[0005] The transistors 101 and 102
Are commonly connected to the source of the transistor 109, the drains of the transistors 103 and 104 are commonly connected to the source of the transistor 110, and the drains of the transistors 109 and 110 are commonly connected to the segment terminal 21. On the other hand, transistor 105
Each drain of transistors 106 and 106 is commonly connected to the source of transistor 111, each drain of transistors 107 and 108 is commonly connected to the source of transistor 112, and each drain of transistors 111 and 112 is commonly connected to common terminal 22.

The LCD controller 4 has a transistor 1
This is a means for generating a control signal for controlling ON / OFF of 01 to 112. More specifically, the LCD controller 4 supplies segment data to each gate of the transistors 101 to 104, supplies common data to each gate of the transistors 105 to 108,
The LCD clock is supplied to each of the gates .about.112. As a result, various paths are sequentially formed between each node of the reference power supply unit 10 and each of the segment terminal 21 and the common terminal 22, and each reference level is output in a predetermined pattern from each of the segment terminal 21 and the common terminal 22. Is done. Then, the voltages output to the segment terminal 21 and the common terminal 22 are supplied to the segment driver or the common driver of the LCD.

[0007]

Now, when an integrated circuit including this kind of voltage generating circuit is manufactured and mounted on an LCD or shipped, it is necessary to test whether or not the circuit functions properly. is there. Then, in this functional test, the reference power supply unit 10 supplies the segment terminal 21 and the common terminal 2.
It is necessary to perform a connection test to determine whether each of the paths up to 2 is formed normally.

Here, in the voltage generation circuit to be tested, four types of reference levels generated from four nodes of the reference power supply unit 10 are output from the segment terminal 21 and the common terminal 22. Therefore, in order to determine whether each path from the reference power supply unit 10 to the segment terminal 21 and the common terminal 22 is normally formed, four types of voltages are output from the segment terminal 21 and the common terminal 22. It is necessary to identify which of the reference levels applies.

However, a tester used for testing this kind of integrated circuit does not determine whether the output signal of the device under test is a high level or a low level when performing a function test of the device under test. Although it is possible, it generally does not have a function of identifying an intermediate level that is neither a high level nor a low level, that is, a level such as the reference levels VLC1 and VLC2 in FIG.

Therefore, in order to determine whether or not four types of reference levels are correctly output from the segment terminal 21 and the common terminal 22 by the tester, the running of the test pattern is stopped at an appropriate timing in the function test. At that time, a very troublesome procedure of measuring the DC voltage output to the segment terminal 21 and the common terminal 22 by a separately provided DC measuring unit has to be taken, and the test time becomes long.

To avoid this inconvenience, each node for generating an intermediate reference level (VLC1, VLC2 in the example of FIG. 3) is provided as a terminal in the integrated circuit, and this terminal is externally connected to a power supply potential or a ground potential. Is forcibly set and a functional test is performed by a tester. According to this method, since only the power supply potential or the ground potential is output from the segment terminal 21 and the common terminal 22, connection of each path from the reference power supply unit 10 to the segment terminal 21 and the common terminal 22 is performed by a function test performed by the tester. Testing can be performed.

However, if this method is adopted, terminals for setting the power supply potential or the ground potential from the outside are required by the number of intermediate reference levels, and unnecessary terminals which are only used for the connection test are not required for the integrated circuit. Must be provided.

The present invention has been made in view of the circumstances described above, and has an integrated circuit capable of performing a connection test without prolonging the test time and without providing extra terminals, and an integrated circuit therefor. It aims to provide a functional test method.

[0014]

Means for Solving the Problems To solve the above-mentioned object,
In order to achieve this, the first aspect of the present invention provides a method in which the power supply voltage and the ground voltage are
Reference power supply that divides voltage to generate multiple reference level voltages
The power supply voltage output from the reference power supply
Any one of the ground voltage and the plurality of reference level voltages.
And an output circuit for selecting and outputting one voltage.
An input terminal of the output circuit and the reference level.
A disconnection switch for controlling connection to the power supply voltage;
Connected between the switch and an input terminal of the output circuit,
Between the input terminal of the output circuit and the power supply voltage or the ground voltage.
And a clamp switch for controlling connection .

The invention according to claim 2 is the invention according to claim 1.
3. The integrated circuit of claim 2, wherein the disconnect switch and the clamp switch
It is characterized by using transistors as switches
You.

The third aspect of the present invention is the first or second aspect.
3. The method for testing the function of an integrated circuit according to claim 1, wherein
Turn off the disconnect switch when testing the road function.
And selectively turning on the clamp switch.
Sign .

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a configuration of an integrated circuit serving as a voltage generating circuit of an LCD according to an embodiment of the present invention. In this figure, parts corresponding to the respective parts shown in FIG. 3 are denoted by the same reference numerals, and description thereof will be omitted.

In this voltage generating circuit, the reference power supply 1
A node generating reference level VLC1 at 0 and transistors 102 and 106 in voltage output circuit 100
The transistor 5 is interposed between the common connection points of the respective sources. Further, a transistor 6 is interposed between a node of the reference power supply unit 10 that generates the reference level VLC2 and a common connection point of the sources of the transistors 103 and 107 in the voltage output circuit 100. These transistors are connected to the reference level VLC during the connection test.
1 and VLC2 generating node and voltage output circuit 10
This is a disconnect switch provided for disconnecting between 0.

Each of the nodes on the opposite side of the reference power supply unit 10 of these disconnect switches is provided with a clamp switch for fixing each of them to a power supply potential or a ground potential. That is, transistors 9 and 10 are clamp switches between the common connection point of each source of transistors 102 and 106 and the power supply line (potential VDD) and between the common connection point of each source of transistors 103 and 107 and the power supply line. Respectively. Further, between the common connection point of the sources of transistors 102 and 106 and the ground line, and between transistors 103 and 107
Transistors 7 and 8 are interposed as clamp switches between the common connection point of the respective sources and the ground line.

The test control register 30 holds control bits for turning on / off each of the disconnection switch and the clamp switch.

According to the present embodiment, a connection test can be easily performed by writing an appropriate control bit into the test control register 30. Hereinafter, a method of performing the connection test will be described with reference to FIG.

In the connection test, the transistors 5 and 6 are turned off by writing a predetermined control bit into the test control register 30, and the transistor 102
And the common connection point of each source of the transistors 103 and 107 is disconnected from the reference power supply unit 10.

In this state, by writing various control bits to the test control register 30, the on / off state of the transistors 7 to 10 as clamp switches is set according to each pattern shown in FIG. Judge the level and perform a connection test.
The details are as follows.

First, when testing whether or not the connection of the transistor whose reference level VLC0 is supplied to the source is performed normally, the transistors 7 and 8 are turned on.
The transistors 9 and 10 are turned off.

In the state where such ON / OFF setting is performed, the power supply potential VDD is set as the reference level VLC0.
However, the ground potential is supplied to the voltage output circuit 100 as the reference levels VLC1, VLC2, and Vss. And
If the connection state of the circuit is normal, the power supply potential VDD is output from each of the segment terminal 21 and the common terminal 22 instead of the reference level VLC1, and the reference level VLC
1, a ground potential is output instead of VLC2 and Vss. That is, although a quaternary signal should be output from each of the segment terminal 21 and the common terminal 22, it is output as a binary value.

Therefore, the four-valued expected value pattern of each output signal of the segment terminal 21 and the common terminal 22 used for the function test is converted into a two-valued expected value pattern.
Perform a functional test using the expected value pattern. That is, in the original expected value pattern, the reference level VLC
A high level is set as an expected value instead of 0, a low level is set as an expected value instead of the reference level VLC1, VLC2 or Vss, and a functional test is performed using a binary expected value pattern obtained by such an operation. It does. By this function test, the reference level VLC0
Can perform a connection test on a transistor supplied to the source.

Next, when performing a connection test of a transistor whose reference level VLC1 is supplied to the source, the transistors 8 and 9 are turned on and the transistors 7 and 10 are turned off.

In the state where such ON / OFF setting is performed, power supply potential VDD is supplied to voltage output circuit 100 as reference levels VLC0 and VLC1, and ground potential is supplied as reference levels VLC2 and Vss. If the connection state of the circuit is normal, the segment terminal 2
1 and the common terminal 22, the reference level VLC
Power supply potential VDD is output instead of 0 and VLC1, and ground potential is output instead of reference levels VLC2 and Vss.

Therefore, in the original expected value pattern used for the function test, the reference level VLC0 or VLC1 is used.
, A high level is set as an expected value, a low level is set as an expected value instead of the reference level VLC2 or Vss, and a functional test is performed using a binary expected value pattern obtained by such an operation. By this functional test, a connection test for the transistors 102 and 106 to which the reference level VLC1 is originally supplied to the source can be performed.

Next, when conducting a connection test of a transistor whose reference level VLC2 is supplied to the source, the transistors 7 and 8 are turned off and the transistors 7 and 10 are turned on.

In the state where such ON / OFF setting is performed, reference levels VLC0, VLC1 and VL
The power supply potential VDD is supplied to the voltage output circuit 100 as C2, and the ground potential is supplied as the reference level Vss. And
If the connection state of the circuit is normal, the reference level VLC0,
Power supply potential VDD is output instead of VLC1 and VLC2, and ground potential is output instead of reference level Vss.

Therefore, in the original expected value pattern used for the function test, a high level is set as an expected value instead of the reference level VLC0, VLC1, or VLC2, and a low level is set as an expected value instead of the reference level Vss. A functional test is performed using a binary expected value pattern obtained by such an operation. By this functional test, a connection test can be performed on the transistors 103 and 107 to which the reference level VLC2 is originally supplied to the source.

As described above, according to the present embodiment, a connection test can be performed by a functional test using only binary determination without determining an intermediate level.

Although the above embodiment has been described by taking as an example a voltage generating circuit that uses three divided resistors and generates four types of reference levels, the scope of the present invention is not limited to this. Rather than using more than three split resistors and
It goes without saying that the present invention can be applied to a voltage generating circuit that generates more types of reference levels than types. In this case, a disconnection switch and a clamp switch may be provided on a path for outputting an intermediate reference level, and the test control register may be configured to control these switches.

[0035]

As described above, according to the present invention, the connection test of the LCD voltage generation circuit can be performed without prolonging the test time and without providing extra terminals. effective.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of an integrated circuit serving as a voltage generating circuit of an LCD according to an embodiment of the present invention.

FIG. 2 is a diagram showing an operation of the embodiment.

FIG. 3 is a circuit diagram showing a configuration of a conventional LCD voltage generating circuit.

[Explanation of symbols]

 10 Reference power supply unit 100 Voltage output circuit 5, 6 Transistor (disconnect switch) 7 to 10 Transistor (clamp switch)

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02F 1/133 G09G 3/36

Claims (3)

(57) [Claims] 1. A method for dividing a voltage between a power supply voltage and a ground voltage into a plurality of
A built-in reference power supply that generates a reference level voltage,
The power supply voltage output from the reference power supply, the ground voltage, and the
One of the reference level voltages
Integrated circuit having an output circuit for selecting and outputting
Te, the connection between the reference level voltage and the input terminal of said output circuit
A disconnecting switch to be controlled, and inserted between the disconnecting switch and an input terminal of the output circuit.
The input terminal of the output circuit and the power supply voltage or the connection.
An integrated circuit, comprising: a clamp switch for controlling connection to a ground voltage . 2. The integrated circuit according to claim 1, wherein a transistor is used as the disconnection switch and the clamp switch. 3. The integrated circuit device according to claim 1 or 2.
A function test method, wherein a function test of the integrated circuit is performed.
Turn off the disconnection switch and turn on the clamp switch.
A function test method characterized by selectively turning on a switch .