- overview, tutorial about the basics of what is DDR4 SDRAM, its technology operation, advantages & disadvantages.

DDR3 is the fourth generation of DDR SDRAM technology.

DDR4 SDRAM brings with it further improvements in overall performance which have ensured it has a significant benefit over the previous generation of SDRAM technology.

With the previous generations of SDRAM well established and widely sued, it was necessary to ensure that the future needs were met. As a result DDR4 SDRAM was developed and introduced.

DDR4 SDRAM basics

DDR4 SDRAM offers some distinct advantages over the previous generations of DDR SDRAM.

  • Data rates:   At the time DDR4 was introduced, it was anticipated that DDR3 would peak at a data rate of 1.6 Giga transfers per second per pin. Accordingly this was set as the entry point for DDR4 SDRAM. This transfer rate is expected to rise to twice this level, i.e. 3.2 Giga transfers per second, with possible increases on this.
  • Operating voltage:   A roadmap has been set up for the DDR4 SDRAM VDD supply voltage to remain at 1.2 volts and then over time be reduced as other technologies change. This will be achieved by keeping by holding VDDQ constant at 1.2V and the I/O voltage stable.
  • DQ bus:   . One of the other performance features planned for inclusion in the DDR4 SDRAM standard are a pseudo open drain interface on the DQ bus.
  • Data width:   DDR4 SDRAM offers three values of data width: x4, x8 and x16.
  • Prefetch:   DDR4 SDRAM architecture uses 8n prefetch with bank groups. This includes two or four selectable bank groups. This enables the DDR4 SDRAM to have separate activation, read, write or refresh operations underway in each of the unique bank groups. This techniques increases the memory bandwidth and efficiency. It is particularly suited for memory applications where small levels of granularity are required.
  • Differential signalling:   For DDR4 SDRAM the clock and strobe lines will utilise differential signalling.

By Ian Poole

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