| 摘要 |
Circuitry for determining timing characteristics, for example, access time, setup time, hold time, recovery time and removal time, of as-manufactured digital circuit elements, such as latches, flip-flops and memory cells. Each element under test is embodied in variable-loop-path ring oscillator circuitry that includes multiple ring-oscillator loop paths, each of which differs from the other(s) in terms of inclusion and exclusion of ones of a data input and a data output of the element under test. Each loop path is caused to oscillate at each of a plurality of frequencies, and data regarding the oscillation frequencies is used to determine one or more timing characteristics of the element under test. The variable-loop-path ring oscillator circuitry can be incorporated into a variety of test systems, including automated testing equipment, and built-in self test structures and can be used in performing model-to-hardware correlation of library cells that include testable as-manufactured digital circuit elements.
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