Method and apparatus for testing a video display chip
First Claim
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1. In a circuit having a plurality of signal lines, a method for testing the electrical integrity of said signal lines, the method comprising:
- applying a first voltage potential to a first end of each signal line;
in a chain of series-connected transistors, biasing each transistor thereof with the potential at a second end of each signal line, said chain of transistors having a first end terminal and a second end terminal, said second end terminal capable of being in a high-impedance state or a conductive state;
applying a second voltage potential to said first end terminal of said chain of transistors; and
detecting a potential at said second end terminal of said chain of transistors;
whereby an open in one of said signal lines is indicated by said second end terminal being in a high-impedance state, and the absence of an open in any of said signal lines is indicated by said second end terminal having a potential between ground potential and said second voltage potential.
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Abstract
A video chip includes test circuitry for detecting opens and shorts. The circuitry includes a series-connected chain of transistors and a test register. There is a circuit for the column lines and for the row lines. A bit pattern is driven onto the column or the row lines and received in the corresponding test circuitry. The pattern is read out and compared against the input pattern to detect faulty lines.
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Citations
20 Claims
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1. In a circuit having a plurality of signal lines, a method for testing the electrical integrity of said signal lines, the method comprising:
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applying a first voltage potential to a first end of each signal line; in a chain of series-connected transistors, biasing each transistor thereof with the potential at a second end of each signal line, said chain of transistors having a first end terminal and a second end terminal, said second end terminal capable of being in a high-impedance state or a conductive state; applying a second voltage potential to said first end terminal of said chain of transistors; and detecting a potential at said second end terminal of said chain of transistors; whereby an open in one of said signal lines is indicated by said second end terminal being in a high-impedance state, and the absence of an open in any of said signal lines is indicated by said second end terminal having a potential between ground potential and said second voltage potential. - View Dependent Claims (2, 3, 4, 5)
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6. In a memory circuit having a matrix of data lines and word lines, a method of testing the electrical integrity of said data lines and said word lines comprising:
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driving a first test pattern onto said data lines at a first end thereof; storing data signals appearing at a second end of said data lines into a first register; comparing said first test pattern against data latched into said first register; driving a second test pattern onto said word lines at a first end thereof; storing data signals appearing at a second end of said word lines into a second register; and comparing said second test pattern against data latched into said second register. - View Dependent Claims (7, 8, 9)
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10. A memory circuit comprising:
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a plurality of storage elements arranged in row and column fashion; a column data register having a plurality of outputs coupled to data lines, each data line coupled to a column of said storage elements; a word selector having a plurality of word select lines, each word select line coupled to a row of said storage elements, each word line having an end distal to said word selector, said word selector being operative to activate any one of said word select lines and further being operative to activate all of said word select lines; and a series-connected chain of transistors, each having a gate terminal coupled to a distal end of one of said word lines, said chain of transistors having a first end being coupled to a power rail. - View Dependent Claims (11, 12, 13, 14, 15, 16)
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17. A test circuitry in a video memory circuit that has a plurality of video storage elements arranged in a matrix form, a plurality of data lines and row select lines coupled to said storage elements, said test circuitry comprising:
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a column data register for receiving a test pattern, said column data register having as many bit positions as there are data lines; a column test register for receiving said test pattern from said column data register via said data lines, said column test register having as many inputs as there are said data lines, said data lines coupling said column test register and said column data register; a row data register for receiving a test pattern, said row data register having as many bit positions as there are row select lines; and a row test register for receiving said test pattern from said row data register via said row select lines, said row test register having as many inputs as there are said row select lines, said row select lines coupling said row test register and said row data register; wherein said column test register and row test register being capable of shifting out their content bits in series. - View Dependent Claims (18, 19, 20)
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Specification