PROGRAMMABLE VOLTAGE DIVIDER AND METHOD FOR TESTING THE IMPEDANCE OF A PROGRAMMABLE ELEMENT
 Inventor: Donald M. Morgan, Boise, Id.
 Assignee: Micron Technology, Inc., Boise, Id.
 Appl. No.: 08/813,063  Filed: Mar. 7, 1997
 Int. CI.6 G01R 19/00; G11C 7/00
 U.S. CI 324/537; 324/550; 324/765;
324/76.11; 327/525; 327/527; 365/201
 Field of Search 324/76.15, 76.24,
324/76.35, 76.54, 536, 537, 550, 76.11, 73.1, 765; 327/55, 56, 57, 525, 526, 527, 564, 566, 276, 277, 281, 284; 365/149, 189.09, 201
 References Cited
U.S. PATENT DOCUMENTS
4,572,971 2/1986 Necoechea 327/108
4,698,589 10/1987 Blankenship et al 365/201
5,539,306 7/1996 Riggio, Jr. 324/158.1
5,654,663 8/1997 McClure et al 327/530
Primary Examiner—-James P. Trammell
Assistant Examiner—Demetra R. Smith
Attorney, Agent, or Firm—Seed and Berry LLP
A programmable voltage divider has normal and test modes ol operation. The divider includes first and second supply nodes, a divider node that provides a data value, and a first divider element that is coupled between the first supply node and the divider node. The divider also includes a controlled node, a second divider element that has a selectable resistivity and that is coupled between the divider node and the controlled node, and a test circuit that is coupled between the controlled node and the second supply node. During the normal mode ol operation, the first and second divider elements generate the data value having a first logic level when the second divider element has a first resistivity, and generate the data value having a second logic level when the second divider element has a second resistivity. The test circuit generates a first voltage at the controlled node during the normal mode of operation, and generates a second voltage at the controlled node during the test mode of operation. The test circuit may generate the first and second voltages by varying its impedance, or by switching in and out one or more fixed voltages.
28 Claims, 7 Drawing Sheets