Coded data generation or conversion – Converter calibration or testing
Reexamination Certificate
1999-04-30
2001-05-08
Williams, Howard L. (Department: 2819)
Coded data generation or conversion
Converter calibration or testing
C341S155000
Reexamination Certificate
active
06229465
ABSTRACT:
This invention relates generally to the testing of analog to digital converters, and more particularly to the use of a built in self test (BIST) structure and method for testing analog to digital converters especially those which are part of a larger principally digital circuit.
BACKGROUND INFORMATION
Electrical circuits on microchips are becoming more complex and are used in many more and more different types of circuits. For example, a circuit which is principally a digital circuit may have an analog component(s) or subcircuit(s) which comprises a part of the circuit. In such case analog signals must be converted to digital signals which means that it must contain an analog to digital (A to D) converter.
Of course, circuits that are formed on chips must be tested. In the past a conventional form of testing has been to apply signals from an external source. This technique however, has several drawbacks. First, and very significantly many of the analog subcircuits do not have external entry points for signals to be applied, and thus testing from external sources becomes difficult when it is desired to test the individual subcircuits as well as the entire circuitry on the chip. Also, when a circuit contains analog circuits and an A to D converter, conventional prior art practice has been to apply analog signals to the analog circuit or to the A to D converter and use the analog signals in a predetermined fashion to test the converter. This presents problems since precisely picking up test points on an analog signal can become difficult and may lead to errors. Thus it is desired to provide an improved test method and circuit or testing A to D converters especially where the A to D converters are contained as subcircuits in larger circuitry, and more particularly when the larger circuitry includes significant amounts of digital circuitry.
SUMMARY OF THE INVENTION
According to the present invention, a method of built in self-testing an analog to digital (A to D) converter containing a plurality of discrete components and the circuitry for such testing is provided. The testing methodology includes dividing the circuit into a number of segments of the discrete components (for testing purposes only) with each segment having the same number of discrete components or an unequal but known number of discrete components. The value of the components individually and collectively of each segment is tested and compared with the value of the corresponding components of at least one other segment, and an output signal is generated of the compared value of the segments being tested. In the preferred embodiment, the components are in a ladder configuration and are either resistors or capacitors.
The testing of the component preferably takes place by impressing constant reference signal (preferably voltage) to at least a portion of one of the segments, sampling and holding this value and then providing a similar reference signal to complementary components of the other of said segments being compared, and comparing the output signal from each segments.
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Bulaga Raymond J.
Cummings Brooks A.
Firth Douglas R.
Harris John L.
Newman Christina L.
Hogg William N.
International Business Machines - Corporation
Jeanglaude Jean Bruner
Williams Howard L.
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