Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
2002-01-02
2004-01-06
Cuneo, Kamand (Department: 2829)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
Reexamination Certificate
active
06674299
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a semiconductor tester, semiconductor integrated circuit and semiconductor testing method for checking the output voltages from a semiconductor integrated circuit.
(2) Description of the Prior Art
With the development of liquid crystal display panels (to be referred to hereinbelow as LCD panels) into high definition, liquid crystal display driver ICs (to be referred to hereinbelow as LCD driver ICs) tend to have a greater number of outputs with a greater number of tonal voltage levels. In general, the tonal voltage levels for a LCD driver IC are determined based on the resistive division ratios or capacitive division ratios to the voltage applied from the reference power input terminal of a gamma control resistive circuit and gamma control capacitive circuit incorporated in the device as a reference voltage generating circuit, and the more the tonal levels there are, the more division ratios are broken down into smaller sections.
In order to achieve display of multi-leveled tones, LCD drivers incorporate digital/analog converters (to be referred to hereinbelow as D/A converters) for converting the input digital image data corresponding to the number of tonal voltage levels into analog tonal voltage outputs and output the tonal voltages. For example, a LCD driver IC for 256 tones of display incorporates 8-bit D/A converters.
In the testing of such a multi-output, multi-tonal LCD driver IC, it is normally checked whether each D/A converter converts all the tones of digital input image data into correct levels of voltage and whether the tonal voltages corresponding to an individual tone are converted equally between all the D/A converters.
The checkout of the IC drivers in this case is generally based on three criteria, namely, the maximum positive and negative deviations of the tonal output voltages from all the output terminals with respect to the ideal voltage for each tonal output voltage level, and the variation of the tonal output voltages from all the output terminals (the sum of the maximum positive and negative deviations among all the output voltage terminals). For example, a device of which the maximum positive deviation and maximum negative deviation of actual tonal output voltages from the ideal tonal output voltage fall outside of ±30 mV and the variation among all the output terminals falls outside of about 35 mV should be rejected as a defective. Thus, the checkout demands a markedly high precision of measurement.
FIG. 1
is a chart showing one example of the tonal voltage output test result. In the example shown in this chart, a product is determined to be non-defective if the absolute values of the maximum positive and negative deviations are equal to or lower than 30 mV and the variation among all the output terminals is equal to or lower than 35 mV.
In the testing of LCD driver ICs, input terminal leakage test, functional operation test, electric current consumption test, etc., are also implemented other than the above-described tonal voltage output test. However, the tonal voltage test takes up to about 80% of the total testing time of all these test items. Further, the trend toward increased number of outputs and tones of LCD driver ICs tends to further increases the time required for tonal voltage output test.
This means that reduction of the testing time taken for the tonal voltage output test is the most critical factor in reducing the testing time and cost of LCD driver ICs.
In order to measure the tonal output voltages accurately, it is preferred that the semiconductor tester should have as many voltmeters of a high precision as the number of the tonal output terminals. But if the device is so configured, it becomes too expensive and large-sized. Therefore, from economic and other view points, the number of voltmeters incorporated in a semiconductor tester has been limited to one to a few.
In order to implement the tonal voltage output test with high accuracy in a short time, various methods have been proposed in consideration of economy.
For example, according to the invention of Japanese Patent Application Laid-Open Hei 10 No. 2935, a semiconductor tester is disclosed which comprises: a multiple number of sample hold circuits for sampling the multiple voltages to be tested from a test specimen such as an LCD driver IC or the like, at the same time, in a single operation; a multiplexer for sequentially selecting the multiple sample hold circuits, one by one, so as to output the selected output; and a checkout circuit for checking whether the voltage to be tested, sequentially output from the multiplexer circuit, is suitable based on the associated upper and lower limit voltages.
This disclosure claims that it is possible to reduce the time taken for tonal voltage output test while keeping the precision of measurement since all the tonal output terminals can be checked by using a limited number of voltmeters of high precision and rapidly switching them.
However, this disclosure does not mention the testing of the variation among output terminals. In this case if the test of the variation among output terminals is implemented, this would be performed by storing the voltages from all the output terminals, extracting the maximum and minimum values among the output terminals, calculating the difference between the extracted maximum and minimum values, and comparing the result with the associated reference value.
However, according to the invention described in Japanese Patent Application Laid-Open Hei 10 No. 2935, since the voltages output from the device to be tested are measured terminal by terminal, the upper and lower limit voltages as the reference values need to be reset for every tone or every test voltage level.
The number of voltage measurements is the product of the number of voltage output terminals of the device to be tested and the number of output voltage tones. That is, a device with many tones and many outputs needs an enormous time for testing, resulting in unfeasibility. For an LCD driver IC having 480 outputs and 256 tones, for example, because two output voltages, positive and negative, are needed for each tone, the number of measurements is calculated as the product of the number of outputs, 480, the number of tones, 256, and 2 for positive and negative, which amounts to about 250,000 checks. If one measurement needs about 0.1 millisecond, the test will take up to 25 seconds for each device.
Other than the time for switching the high-precision voltmeter to each tonal voltage terminal, the time needed for one measurement is also largely dependent on the voltage measurement time for actually measuring each tonal voltage and the calculation time for calculating the amount of output variation from terminals. Therefore, even if the switching time of the high-precision voltmeter to each tonal voltage terminal can be made short, it is impossible to sharply reduce the time of measurement. So there remains the problem of reducing the measurement time as long as the test is performed by measuring all the output voltages.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a simple and low-cost semiconductor tester, semiconductor integrated circuit and semiconductor testing method, which make it possible to perform rapid check of output voltages from a multiple number of output terminals of a semiconductor integrated circuit.
In order to achieve the above object, the present invention is configured as follows:
In accordance with the first aspect of the present invention, a semiconductor tester for checking the output voltages of a semiconductor integrated circuit having a multiple number of output terminals which output predetermined voltages, includes: a judgement means which, with reference to the mean voltage value of the voltages output from all the output terminals of the semiconductor integrated circuit, judges the suitability of the output voltage from each of the output terminals.
In accordance with the second
Birch & Stewart Kolasch & Birch, LLP
Cuneo Kamand
Nguyen Trung
Sharp Kabushiki Kaisha
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