Static information storage and retrieval – Read/write circuit – Testing
Patent
1997-08-22
1999-05-18
Hoang, Huan
Static information storage and retrieval
Read/write circuit
Testing
36518909, 36518911, G11C7/00
Patent
active
059056827
ABSTRACT:
A substrate biasing circuit operates in either a test mode or a normal operating mode. The substrate biasing circuit includes a voltage generating circuit generating a substrate biasing voltage at an output terminal and a control terminal controlling the magnitude of the substrate voltage. When the voltage at the control terminal is more positive than a predetermined value, the voltage generating circuit gradually drives the substrate more negative. When the voltage at the control input of the voltage generating circuit is less than the predetermined value, the output terminal of the voltage generating circuit essentially floats. In normal operation, the output terminal of the voltage generating circuit is also coupled to the control terminal so that the substrate voltage is regulated at the predetermined negative voltage. Alternatively, the substrate may be coupled to ground and the voltage generating circuit disabled during normal operation. In a test mode, the control terminal is coupled to an externally accessible input terminal. Respective impedance elements between the control terminal and the input terminal and between the control terminal and the output terminal form a voltage divider. As a result, the substrate voltage is adjusted as a function of a voltage applied to the input terminal to maintain the control terminal of the voltage generating circuit at the predetermined value. The control terminal may be coupled to the input terminal through a pass gate which may be controlled by a decode circuit to selectively isolate the control terminal from the externally accessible input terminal during normal operation.
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Micron Semiconductor, Inc., Schematic of Circuit used in DRAMs since before Aug. 15, 1995. (single schematic, 2 pages).
Gans Dean D.
Wilford John R.
Hoang Huan
Micro)n Technology, Inc.
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