DFE: a Technique to Increase the Speed in DDR5 Memories

One of the biggest problems JEDEC is currently facing for RAM is achieving higher bandwidths based on higher frequencies. All without making mistakes in reading, writing or copying at any time and also using a lower general voltage. How exactly do they do it? It is not just a technique they use, but if we had to highlight one insurance it would be the well-known DFE .

The key word or concept, not just in DDR5 , but in memories in general is certainly mitigation. Mitigation in itself can come in different ways, but the most useful is certainly when combined with prevention.

DDR5

Compensation, mitigation and prevention are the foundations of DFE

DFE 3

DFE is the acronym for Decision Feedback Equialization , translated as a concept similar to decision feedback equalization and is a technique that is being used in wide fields of computing for its benefits to achieve better speeds.

To explain what DFE is, we will have to give some examples, since the definition itself is not too instructive: it is a technique that compensates for the malfunction of certain previously poorly executed bits.

From the memory point of view, we will have to imagine a dummy RAM channel, where a series of zeros are sent continuously, then a single 1 and then another series of continuous zeros. To change from zero to one, a jump is needed in the transmitter and the channel, but to achieve this it is necessary that the speed and response time are as short as possible so as not to be misleading and thus reach the threshold for the memory to record the 1.

DFE 1

In the image above you can see how the memory threshold is always low, about -1.5V (it is not the general voltage of the same obviously), and when 1 tries to register and needs to exceed said threshold of zero so that it remains constancy, the voltage is not even able to offer the zero value.

DFE 2

If the memory knows that the value that preceded 1 was zero, the new DDR5 will be able to lower the threshold below or may increase the voltage more than what is established, whichever is best to be able to register 1 as such.

Higher frequencies will determine better chips, more durable and with more tolerances

DFE 4

This is useful when the frequency is struggling to adapt to new heights and you are having a hard time safeguarding the data log. This of course is applicable to a much longer bit string, where complexity and speed multiply as well as changes in VREF voltages .

The key advantage of using DFE is that the noise is not amplified along with the signal because the change in voltage is only due to the digital values it works with and therefore the signal remains clean.

DDR5

The only thing designers of platforms and systems have to consider is that the number of DFE per second is realistically limited on each system.

These voltage variations have an impact on the power consumption as on the silicon of the NAND Flash themselves, so it will be interesting to see how the system evolves in the hands of memory manufacturers and how much durability they certify.