| 摘要 |
A method and apparatus for efficiently testing input/output (I/O) buffer are disclosed. The I/O buffer includes multiple transistors coupled to a data output terminal. The method includes enabling a single one of the multiple transistors. A predetermined electrical voltage level is then forced upon the data output terminal, and a resultant electrical current flowing through the data output terminal (e.g., in a direction away from the I/O buffer) is measured. The measured electrical current is compared to predetermined minimum and maximum current values. A ratio of the measured electrical current to a reference current is computed, and the computed current ratio is compared to a predetermined minimum and maximum current ratio. The above steps may be repeated until each of the multiple transistors has been enabled. The drive strength of a given transistor is a measure of the amount of electrical current the transistor causes to flow through the data output terminal when enabled. One or more of the multiple transistors has a drive strength which is less than all of the other transistors (i.e., a minimum drive strength). The reference current may be the amount of electrical current flowing through the data output terminal with the predetermined voltage level forced thereupon when the single enabled transistor has the minimum drive strength. By testing the impedances of the individual transistors of an I/O buffer independently, the method and apparatus accomplish I/O buffer testing in a highly efficient manner.
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