Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
1998-09-25
2001-08-28
Karlsen, Ernest (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
Reexamination Certificate
active
06281700
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an active matrix substrate inspecting method, an active matrix substrate, a liquid crystal device and an electronic apparatus. In particular, the invention relates to techniques for inspecting a type of active matrix substrate in which a digital data-line driver, i.e., a driver in which a digital signal is input and converted from digital to analog form to output an analog signal for driving data lines, (hereinafter referred to as a “digital driver”) is formed on the substrate.
2. Description of the Related Art
In recent years, research has been conducted on an active matrix substrate with a built-in driver in which driving circuits (drivers) for scanning lines and data lines are formed on a substrate, and a liquid-crystal display device using the substrate. Such an active matrix substrate is produced using low-temperature polysilicon techniques, for example. In order to sell the products, which use the above active matrix substrate, on the market, it is necessary to accurately perform a testing of good or bad products from the perspective of guaranteeing reliability prior to the panel assembly after the substrate is formed.
According to a study conducted by the present inventor, the above-described inspection mainly requires basic inspections, such as checking the drivers' output ability and detecting a disconnection of the data lines, and inspections of the characteristics of switching devices (TFTs, MIMs, etc.) included in pixels as well as the leak characteristics of storage capacitors, which relate to an inspection on a point defect in an active matrix unit.
In the case of a digital driver for driving the data lines (namely, digital-data-line driver), a method for performing simultaneous driving at predetermined timing (line-at-a-time driving method) has been employed by paying attention to the ease of digital data storing.
A display device with such built-in digital-line-at-a-time-driving driver has not been realized, so that the manner in which the above-described highly reliable inspections are performed is not clear.
SUMMARY OF THE INVENTION
Therefore, one of the objects of the invention is to establish a testing technology of the active matrix substrate in which a digital driver is loaded and to sell substrates, display devices, or the like with high reliability on the market.
In order to accomplish this object, the invention has the following structures.
The invention includes:
a plurality of scanning lines and a plurality of data lines;
a digital driver that enables an output terminal to be in a high-impedance condition, the digital driver being provided for driving the plurality of data lines;
switching devices connected to each scanning line and each data line;
capacitors connected to the each of switching devices; and
an inspection circuit provided at ends of the data lines opposite to the digital driver, the inspection circuit including bi-directional switches provided for each of the plurality of data lines, and control means for controlling the switching of the switches.
Because the digital driver for the data lines has a D/A converter in an output unit, an active matrix unit testing (measurement of point defects) cannot be performed by reading the signal again which was once output through the common channel.
However, according to the invention, since the inspection circuit is provided at the opposite ends of the data lines to the digital driver, signals can be written in the capacitors (storage capacitors) in the active matrix unit by driving the data lines with the digital driver, and the written signals can be read out through the inspection circuit. Accordingly, determination of whether or not there is a point defect can be made.
In the case of the signal reading with the inspection circuit, when the output of the digital driver (A/D conversion output) is turned on, defect determination based on signals read out from the storage capacitors is not secured. Thus, in order to acquire a basic signal for point-defect determination, the output of the inspection circuit needs to be switched off (set to be in a high-impedance condition). Therefore, the digital driver includes the function of enabling the output to be in a high-impedance condition.
In addition, since the inspection circuit is provided as a circuit used for inspection, it does need to operate at high speed like the digital driver, and it only needs a minimum function, for example, being capable of performing inspection. Accordingly, in accordance with the invention, the digital driver has a structure including bi-directional switches, e.g., analog switches, and control means for controlling the switching of the switches. The digital driver's simplified circuit arrangement and the fact that it is not required to have advanced operating characteristics enables it to be a small transistor size, which provides the advantage of space reduction. Therefore, the inspection circuit can be mounted on the active matrix substrate easily.
The “inspection circuit” means a circuit that is mainly used for inspection and not having the function of driving the data lines like the digital driver. However, the “inspection circuit” can have another object which is different from inspection, and it can include a component that can be used to accomplish an object other than inspection.
Devices included in the inspection circuit are produced, together with devices included in the digital driver, by an identical production process.
On one active matrix substrate, a digital driver and an inspection circuit are produced by an identical process. For example, using low-temperature polysilicon-thin-film-transistor (TFT) techniques enables their production.
The digital driver includes a switch in its output unit, and opening the switch causes the output unit to be in a high-impedance condition.
The switch is provided in the output unit in order to make the output of the digital driver be in a high-impedance condition.
The digital driver includes any one of a switched capacitor D/A converter, a resistor ladder D/A converter and a PWM D/A converter.
Examples of a D/A converter that is mountable on an active matrix substrate in accordance with the invention are described below.
In a switched capacitor D/A converter, for example, switches are provided for each of the weighted capacitors, and the charge of each capacitor is combined with a coupling capacitor by control of the switching of the switches so as to generate a conversion voltage.
In a resistor ladder D/A converter, for example, a resistance-divided voltage is selectively extracted by control of the switching of the switches provided at the output channels so as to generate a conversion voltage.
In a PWM D/A converter, for example, the on-duration of a switch connected to a voltage source in which a voltage value varies with time (ramp-wave) is controlled in accordance with a digital data value so as to generate a conversion voltage.
The control means in the inspection circuit performs point-at-a-time scanning of the bi-directional switches.
The inspection circuit has, for example, a point-at-a-time scanning system of data lines using shift registers, etc. and performs inspection by the point-at-a-time reading of data.
When the number of the bi-directional switches is M, where M is a natural number not less than 2, the control means in the inspection circuit repeatedly performs the simultaneous driving of P, where P is a natural number, bi-directional switches Q, where Q is a natural number, times, whereby the driving M (M=P×Q) of bi-directional switches in total is realized.
The inspection circuit uses a method different from point-at-a-time scanning.
At least a part of the inspection circuit is disposed in a space, which is in the active matrix substrate and not contributing to the realization of substantial functions, such as displaying an image.
Since the inspection circuit only needs to be a small transistor size and thus only occupies a small area, at least a part o
Karlsen Ernest
Oliff & Berridge PLC.
Seiko Epson Corporation
Tang Minh
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