JPS6267479A - Dot matrix system display unit - Google Patents

Abstract

PURPOSE:To enable selection at a high quality, by incorporating a decision circuit capable of varying a decision level by an external signal to permit the detection of difference and variations in the driving capacity of a transistor according to the results of responding to a plurality of decision levels. CONSTITUTION:A reference level for deciding on the quality of a circuit at a pixel section is applied to a set terminal 12 of a decision circuit 4 from an external terminal Vs and a test operation is started. In the operation, an input control transistor Trin, a train selection transistor Tr4 and a writing transistor Tr1 are closed and a signal is inputted from a terminal Vv to be stored into a storage capacitance Cv. The voltage level at an output terminal T' where the stored signal is read out is compared with the reference level by the decision circuit to decide on the driving capacity of a corresponding pixel. Upon the completion of testing over the entire surface, the reference level is altered several times as required and the same test is carried out. This enables the discrimination of variations in the driving capacity of a transistor at the pixel part.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention provides a testable dot matrix, which includes a display drive transistor, a write transistor, and a read transistor for each unit pixel arranged in a dot matrix. This invention relates to a method display device.

<Prior Art> Conventionally, in a matrix-type display device having a display drive transistor for each unit pixel, the means for determining whether each pixel is good or bad is as follows:
The method used to make a display device was to actually perform two displays and make a judgment, but electrical testing is now possible by providing a readout transistor for each pixel using the technique described in Japanese Patent Application Laid-Open No. 57-99688. It was. However, according to this method, data corresponding to "open" or "close" of the drive transistor is written in each pixel, and then an external determination circuit is driven through the readout transistor to detect the state of the drive transistor. Time,
The disadvantage is that the load such as the capacitance and resistance of the connection line with the outside is large, and it takes time to make a determination for each pixel.

Therefore, the same applicant as the author devised a dot matrix type display device that solved the above-mentioned drawbacks, and filed an application on July 5, 1985. This display device can be
To briefly explain the drawings, in a device in which display elements 3 arranged in a dot matrix are driven by a vertical scanning circuit 1 and a horizontal scanning circuit 2, each display element 3 has a write transistor Tr1. Display drive transistor Tr2. A readout transistor Tr3 and an input signal storage capacitor CV are provided, and a column selection transistor Tr3 is provided.
4 is selected. When testing a certain pixel, if we consider the case of testing the pixel in the first column and jth row, as shown in the example above, each transistor Tr2. Tr3. Tr4.
An inverter is formed by the control transistor Trsw and the load element Re. At this time, if the circuit is normal, the potential of the terminal T' of the inverter is determined according to the signal stored in the storage capacitor Cv. The terminal T′ determined in this way
A determination circuit 1nv consisting of an impark determines whether the potential of
Output through ut. At this time, by determining the constants that can sufficiently drive the external circuit in the design of the judgment circuit (nv), it is possible to easily drive the externally connected load, which speeds up the test. be.

<Problems to be Solved by the Invention> Although the display device has a remarkable effect of speeding up the determination of whether a unit pixel is good or bad, a few problems remain. That is, in the above device, although it is possible to determine whether the transistor constituting each pixel is short-circuited or disconnected, the determination circuit 1nv
Since the determination level of "good" and "bad" is always constant and cannot be changed, it is difficult to detect the difference in the driving ability of each transistor. By the way, in this type of display device, subtle differences in display brightness, reflectance, transmittance, etc. for each pixel impair the display quality and result in a defective product, but the difference in the driving ability of the transistors mentioned above This causes subtle differences in display. Therefore, in the test using the above-mentioned device, it is not possible to determine whether the display device is of high quality or has some quality defects.

The present invention has been made in view of the above-mentioned conventional problems and to solve the problems, and by externally varying the judgment level for determining whether the output signal of the inverter is high or low, It is an object of the present invention to provide a dot matrix display device that can detect differences and variations in driving ability of transistors and select high-quality display devices.

Means for Solving Problems> In order to achieve the above object, the present invention arranges unit pixels in a matrix, and for each pixel, a drive transistor for driving a display body and a video signal for driving are provided. In a dot matrix type display device, which has a write transistor for supplying the signal and a read transistor for extracting the output level of the drive transistor to the outside, and is capable of electrically testing the circuit constituting each pixel for each pixel. The gist of the present invention is to have a configuration including a determination circuit that determines whether the circuit is good or bad, and whose signal level is externally variable.

<Example> Hereinafter, one embodiment of the present invention will be explained in detail.

In FIG. 1, the same reference numerals are given to the same or equivalent components as in FIG. This differs from the one shown in FIG. 3 in that it is replaced with a determination circuit 4 consisting of a comparison circuit with the signal at the output terminal T of the circuit. Details of the determination circuit 4 are illustrated in FIG. 2, and MOS-FETs Tr13 to Tr1
6 is configured as a differential amplifier circuit.

The operation of the embodiment apparatus configured as described above will be explained. As shown in FIG. 1, consider the case where a pixel in the i-th column and j-th row is tested. First, a reference level for determining whether the circuit in the pixel section is "good" or "defective" is applied to the setting terminal 12 of the determination circuit 4 from the external terminal Vs, and then a test operation begins. Input control transistor Trin, column selection transistor Tr4. The write transistor Trl is closed, a signal is input from the terminal Vv, and the signal is stored in the M product capacitor CV. At this time, output control transistor TrOutl load control transistor Trsw
, the read transistor Tr3 is left open. After that, each transistor Trin, Tr4 . Trl
Transistor Tr3. Tro
By closing ut and Trsw, each transistor T
r2.

Tr3. Tr4. An inverter is formed by Trsw and load element Re. At this time, if the circuit is normal, M
The potential level of the output terminal T' is determined according to the time since the start of reading out the signals accumulated in the customer service MCv. The determination circuit 4 compares the level of the output terminal T' thus determined with the reference level, and outputs the result from the output terminal VV.

Next, the operation of the determination circuit 4 will be explained. When the signal level of the output terminal T' is determined, the MOS-FETTrll, Tr
i2 is closed, and the reference level and the signal level at the output terminal T' are taken into both input terminals 11 and 12 of the determination circuit, respectively.

At this time, MOS-FETTr13. Tri4. Tri7
Leave it open. Next, MOS-FET Trll, T
At the same time as opening ri2, MOS-FET Tr13. T
When ri4°Tri7 is closed, the difference between the signal level at the output terminal T' and the reference level is amplified, and this output is output from the output terminal Vv terminal as a test result through the output control transistor "l" r out. Note that the clock φ, 7 is externally applied so that each transistor of the determination circuit operates as described above. In this way, the input signal and output signal are compared to determine the driving ability of that pixel. When the test for one pixel is completed, the next pixel is sequentially selected and the same test is performed.

Once the overall test is complete, repeat the same test by changing the reference level several times as necessary to determine variations in the driving ability of the transistors in the pixel area, and create a device with uniform driving ability. It is possible to select display devices with good display quality.

<Effects of the Invention> As is clear from the above description, the dot matrix display device of the present invention has a built-in determination circuit that can vary the determination level by an external signal.
Differences and variations in the driving ability of transistors can be detected based on the response results for a plurality of determination levels, and high-quality display devices can be selected.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the dot matrix type display device of the present invention, FIG. 2 is an electric circuit diagram of the determination circuit shown in FIG. 1, and FIG. 3 is a block diagram of a conventional device. Tri...-Write transistor Tr2--Drive transistor Tr 3-Read transistor 4-Judgment circuit Vs-External terminal

Claims (1)

[Claims] (1) Unit pixels are arranged in a matrix, and each pixel has a drive transistor that drives the display, a write transistor that supplies video signals for drive, and a drive transistor that extracts the output level of the drive transistor to the outside. In a dot matrix display device having a readout transistor and capable of electrically testing a circuit constituting each pixel, a signal for determining whether the circuit is good or bad. A dot matrix display device characterized by comprising a determination circuit whose level can be changed externally.