Sun Microsystems, Inc.

Oracle America, Inc.

Oracle International Corporation

Daniel Fung

Dennis L Wendell

Jun Liu

Yolin Lih

Ajay Bhatia

Shyam Sundar Balasubramanian

John Gregory Favor

Joseph Byron Rowlands

Laurent Rene Moll

Hoyeol Cho

Ioannis Orginos

Systems and methods are described herein that reduce the read latency of a cache by separating read and write column select signals that cause the cache to initiate certain read and write operations, respectively.

Separate read/write column select control

A memory device having a split power switch is provided to improve the writeability of static random access memory (SRAM) cells without adversely compromising their stability. For example, various split power switch circuits are used to permit the voltage or current of a power supply line connected with one side of an SRAM cell to drop during write operations. This drop weakens one side of the SRAM cell and reduces the drive-fight between transistors of the SRAM cell and external write circuitry. As a result, the minimum voltage for writing new logic states into the SRAM cell is reduced to permit overall lower operating voltages for the SRAM cell and related circuitry. By continuing to maintain a second side of the SRAM cell at the reference voltage or current, the SRAM cell can successfully switch to a newly written logic state.

Memory device with split power switch

An elastic power header device and methods of operation are provided to improve the read margin of static random access memory (SRAM) cells by increasing read stability, reducing read disturbance and improving the Signal to Noise Margin (SNM) figure of merit. For example, various implementations of an elastic power header device are utilized as programmable resistances to permit the power supply lines to reach a maximum voltage. Allowing the power supply lines to reach the reference voltage allows more flexibility in read margin and read stability. Furthermore, this additional flexibility can be controlled by means for adjusting a voltage. This adjustment voltage can fine-tune the programmable resistances so that the read margin can be more conveniently controlled.

Elastic power for read margin

An elastic power header device and methods of operation are provided to improve both the read and the write margin of static random access memory (SRAM) cells by increasing read stability, reducing read disturbance and improving the Signal to Noise Margin (SNM) figure of merit. For example, various implementations of an elastic power header device are utilized as programmable resistances to permit the power supply lines to reach a maximum voltage. Allowing the power supply lines to reach the reference voltage allows more flexibility in read margin, write margin and read stability. Furthermore, this additional flexibility can be controlled by means for adjusting a voltage. This adjustment voltage can fine-tune the programmable resistances so that the read margin and the write margin can be more conveniently controlled.

Elastic power for read and write margins

A reduced-power memory (such as for a cache memory system of a processor or a microprocessor) provides per-sector power/ground control and early address to advantageously reduce power consumption. Selective power control of sectors comprised in the reduced-power memory is responsive to a subset of address bits used to access the memory. The selective power control individually powers-up a selected one of the sectors in response to an access, and then powers-down the selected sector when the access is complete. The power-up is via an increase of differential between power and ground levels from a retention differential to an access differential. Time needed to vary the differential is masked by providing address information used by the selective power control in advance of providing other address information. For example, in a cache, a tag access is overlapped with power-up of a selected sector, thus masking latency of powering up the selected sector.

Reduced-power memory with per-sector power/ground control and early address

A reduced-power memory (such as for a cache memory system of a processor or a microprocessor) provides per-sector ground control to advantageously reduce power consumption. Selective power control of a plurality of sectors comprised in the reduced-power memory is responsive to a subset of address bits for accessing the memory. The selective power control individually powers-up a selected one of the sectors in response to an access, and then powers-down the selected sector when the access is complete. The power-up is via a decrease in ground potential from a retention level to an access level. Time needed to vary the ground potential is optionally masked by providing address information used by the selective power control in advance of providing other address information. For example, in a cache, a tag access is overlapped with power-up of a selected sector, thus masking latency of powering up the selected sector.

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Fremont, CA, United States of America

Daniel Fung