International Business Machines Corporation

Richard Thomas Dennison

David B Eardley

Leo Boyes Freeman

Peter Tsung-Shih Liu

Helen Janet Kelly

A split random access memory array is integrated with a read only storage array and shares the same sense and bit decode circuitry. Each bit line of the integrated array is provided with an isolation switch between the random access and read only portions. The switch conducts when reading the read only portion but does not conduct (isolates) when writing or reading the random access portion. The isolation switch also permits the initialization of the shared differential sensing latch and facilitates the rapid writing and reading of the random access portion by removing the bit line loading due to the read only portion on such occasions.

Split memory array sharing same sensing and bit decode circuitry

The disclosure is an improved Random Access Memory (RAM) integrated circuit chip. More specifically, enhancement - depletion mode field effect transistor technology is employed to provide a solid state memory having improved 'reading' and 'writing' capability. A pair of N-channel depletion mode devices are used to initialize the bit lines before the start of the next read or write cycle. These devices are switched to a high conductive state resulting in a rapid initialization of the bit lines. A sense latch circuit incorporating enhancement and depletion mode devices is used to detect and latch a small differential signal on the bit lines. The state of the sense latch is isolated from and does not affect the bit line voltages at any time during the memory cycle. M pairs of N-channel depletion mode devices are provided. One pair for each of B/S lines. M sense latch circuits are provided. One for each pair of B/S lines. In addition, there is provided a final sense latch circuit which is employed as the final latch in the bit circuits. The final sense latch is set with the data from a selected one of said M sense latch circuits. The final sense latch circuit provides an output which drives a data output driver.

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Hopewell Junction, NY, United States of America

Richard Thomas Dennison