Mobile DDR

Mobile DDR (also known as mDDR, Low Power DDR, or LPDDR) is a type of double data rate synchronous DRAM for mobile computers.

Just as with standard SDRAM, each generation of LPDDR has doubled the internal fetch size and external transfer speed. Maximum transfer rates are:

In contrast with standard SDRAM, used in stationary devices and usually connected over a 64 bit wide memory bus, LPDDR also permits 16- or 32-bit wide channels.

The original low-power DDR (sometimes, in hindsight, called LPDDR1) is a slightly modified form of DDR SDRAM, with several changes to reduce overall power consumption.

Most significant, the supply voltage is reduced from 2.5 to 1.8 V. Additional savings come from temperature-compensated refresh (DRAM requires refresh less often at low temperatures), partial array self refresh, and a "deep power down" mode which sacrifices all memory contents. Additionally, chips are smaller, using less board space than their non-mobile equivalents. Samsung and Micron are two of the main providers of this technology, which is used in tablet computing devices such as the Apple iPad, Samsung Galaxy Tab and Motorola Droid X.

A new JEDEC standard JESD209-2E defines a more dramatically revised low-power DDR interface. It is not compatible with either DDR1 or DDR2 SDRAM, but can accommodate either:

Low-power states are similar to basic LPDDR, with some additional partial array refresh options.

Timing parameters are specified for LPDDR-200 to LPDDR-1066 (clock frequencies of 100 to 533 MHz).

Working at 1.2 V, LPDDR2 multiplexes the control and address lines onto a 10-bit double data rate CA bus. The commands are similar to those of normal SDRAM, except for the reassignment of the precharge and burst terminate opcodes:

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