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DDR SDRAM Power Reduction Method in Suspend (Self Refresh) State

IP.com Disclosure Number: IPCOM000015578D
Original Publication Date: 2002-Feb-09
Included in the Prior Art Database: 2003-Jun-20
Document File: 1 page(s) / 55K

Publishing Venue

IBM

Abstract

Disclosed is a power reduction method of DDR SDRAM in suspend (self -refresh) state. The main idea is to turn off the power supply to the parallel termination resistors (Vtt) during the suspend (self-refresh) state. In the suspend (self-refresh) state, the chipset needs to drive only the CKE (clock enable) out of DDR SDRAM signals to low and can make the other signals float (Hi-Z). Therefore, the system can turn off the Vtt during the suspend state. Turning off the Vtt saves the current from the Vtt througth the termination resistors to the chipset CKE output pin. In a typical implementation, the Vtt is 1.25 volts and the parallel terminator is 50 ohm, the series terminator is 25 ohm. Therefore, approximately 17mA is saved per one CKE line. The DDR SDRAM SO-DIMM, which will be popular for the notebook DDR solution, has two CKE's. In case that the system has two DIMM slots, the total power saving during the suspend (self-refresh) is as follows:

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DDR SDRAM Power Reduction Method in Suspend (Self Refresh) State

Disclosed is a power reduction method of DDR SDRAM in suspend (self -refresh) state.

    The main idea is to turn off the power supply to the parallel termination resistors (Vtt) during the suspend (self-refresh) state. In the suspend (self-refresh) state, the chipset needs to drive only the CKE (clock enable) out of DDR SDRAM signals to low and can make the other signals float (Hi-Z). Therefore, the system can turn off the Vtt during the suspend state.

    Turning off the Vtt saves the current from the Vtt througth the termination resistors to the chipset CKE output pin. In a typical implementation, the Vtt is 1.25 volts and the parallel terminator is 50 ohm, the series terminator is 25 ohm. Therefore, approximately 17mA is saved per one CKE line.

    The DDR SDRAM SO-DIMM, which will be popular for the notebook DDR solution, has two CKE's. In case that the system has two DIMM slots, the total power saving during the suspend (self-refresh) is as follows:

1.25 (volt) / ( 25 + 50 (ohm) ) * 2 (CKE line) * 2 (slot) = 0.067 (ampere)
1.25 (volt) * 0.067 (ampere) = 0.083 (watt)

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