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DDR4 SDRAM FAQs

DDR4 SDRAM(16)
What are some of the additional power-saving features of DDR4?

Some new power-savings features in DDR4 include pseudo open-drain DQs (for read and write I/O power reduction), data-bit inversion (DBI), and command address latency (CAL).

What is the value of DDR4?

DDR4 has more than 20 new features compared to DDR3—multiple power-saving, performance, and reliability features. These features, coupled with DDR4’s 1.20V core, can provide as much as 40% power savings compared to standard DDR3. With the new DDR4 architecture and added performance features, a substantial performance boost in bandwidth and command scheduling can be realized for 100% or better effective bandwidth increase. In addition, while mainstream DDR3 is at 1600 MT/s today, DDR4 will start at 2400 MT/s, eventually reaching 3200 MT/s.

Can DDR4 operate at slower DDR3 speeds?

DDR4 is backward compatible as far back as DDR3-1333. For systems that do not need speed increases above DDR3-1333 and DDR3-1600, DDR4 can support these slower bandwidth requirements with substantially lower power requirements.

Will DDR4 be a replacement for your DDR3 offering?

Just as DDR2 transitioned to replace DDR memory, and DDR3 transitioned to replace DDR2 memory, DDR4 will also transition to replace DDR3 memory as the volume commodity DRAM. We expect industry DDR3 to DDR4 crossover to occur in the 2015 timeframe. For designs that cannot afford a re-spin to DDR4 SDRAM, we expect to still provide DDR3 SDRAM as DDR3 enters the legacy support phase. In the meantime, DDR4 is a great alternative for systems needing power savings or a performance bump from DDR3; every new memory design should at least adopt DDR4 support.

How does this product compare to your competition in the DDR4 market?

We’re first to sample a fully functional, JEDEC JESD79-4-compliant DDR4 SDRAM, as well as functional test modules, well ahead of JEDEC DDR4 module standardization. Our initial DDR4 parts meet the industry’s advance projections for the JEDEC specification and will progress to meet the finalized JEDEC standard, as well.

Why is Micron behind the competition in delivering DDR4 samples?

Although Micron didn’t provide the first DDR4 sample, which consisted of a die with DDR4 logic on it, Micron was the first to provide a fully functional sample that was JEDEC JESD79-4-compliant. Micron’s DDR4 sample is the first production-quality DDR4 offering available.

Where will DDR4 devices be manufactured?

DDR4 will be produced in Micron fabs around the world, including Virginia, Singapore, and Taiwan.

Are there any features on DDR3 that have been eliminated by DDR4?

Not really; however, DDR4 does not require an external VREFDQ, but it does provide an internally generated VREFDQ that requires calibration by the DRAM controller.

Does DDR4 use the same signaling protocol as DDR3?

DDR4 uses the same VTT mid-point termination methodology (SSTL1.5) on the address, command, and control pins as DDR3; however, DDR4 uses VDD termination (POD12) on the data bus due to the use of pseudo open-drain I/Os for improved signal quality and less switching current.

Does DDR4 use the same power sources as DDR3?

No, DDR3 requires VDD and VDDQ equal to 1.5V, VREFCA equal to 0.5 x VDD, and VREFDQ equal to 0.5 x VDDQ, while DDR4 requires VDD and VDDQ equal to 1.2V, VREFCA equal to 0.5 x VDD, and VPP equal to 2.5V.

What is DDR4’s VPP supply, and why does DDR4 have it?

The VPP supply replaces the internal word-line charge pumps. Providing this voltage externally allows the DDR4 to operate at a lower voltage level in a more cost-effective manner rather than providing the internal charge pumps.

Are DDR3 and DDR4 pin-to-pin compatible to each other?

No, the DDR4 ballout is different from the DDR3 ballout. However, DDR4 uses the same package sizes and ball pitch as DDR3.

DDR4 doubled the data rate of DDR3—did the prefetch also double from 8n to 16n?

No, DDR4 kept the 8-bit prefetch used by DDR3; thus, BL8 is still supported.

Did DDR4 finally add boundary-scan or JTAG support?

For x16 devices, yes; DDR4 added a “connectivity test” mode that allows electrical verification of balls after connection to a memory interface.

Are there any new inputs/outputs required to support DDR4?

Yes, seven new inputs/outputs were added: VPP, BG (bank group), DBI_n, ACT_n, PAR, Alert_n, and TEN. However, the ball count increased by only three (73 to 76 balls).

Does DDR4 support DLL off mode for very slow clock rates?

Yes, DDR4 supports DLL-off mode similar to DDR3, up to 125 MHz.