But spec told us that the total capacitive loading on the ZQ pin must be limited. We can see the table For detail things, advising you to reading the spec seriously. Everyone has his own understanding, if you have any question, please let me know, i'm glad to talk with u. So it would be my next target. The temperature, voltage and process differences of SDRAM particles are considered during the verification.
It is responsible for sending data back during reads and receiving data during writes. The resistance is even affected due to voltage and temperature changes. So, they are made tunable. When a ZQCL command is issued during initialization, this DQ calibration control block gets enabled and it produces a tuning value. This value is then copied over to each DQ's internal circuitry. Ok, the above explanation is a quick overview of ZQ calibration. If you're satisfied, proceed to the next section.
If you're itching for more details, read on. These little transistors are set based on input VOH[]. Every PCB layout is different so this tuning capability is required to improve signal integrity, maximize the signal's eye-size and allow the DRAM to operate at high-speeds.
Get notified when a new article is published! This was done to improve signal integrity at high speeds and to save IO power. Take another look at the left-hand side of Figure 8, the receiver is essentially a voltage divider circuit.
But in DDR4 there is no voltage divider circuit at the receiver. It instead has an internal voltage reference which it uses to decide if the signal on data lines [ DQ ] is 0 or 1. This voltage reference is called VrefDQ. Let's take a closer look at our example system.
This is done because all DRAMs on the DIMM share the same address lines and fly-by routing is required to achieve better signal integrity and the high speeds.
The DRAM is a fairly dumb device. The memory controller needs to account for the board trace delays and the fly-by routing delays and launch Address and Data with the correct skew between them so that the Address and Data arrive at the memory with CWL latency between them. The height reduction improves airflow in the system, thus improving cooling. Figure 6. Memory modules are typically organized as either or 72 bit wide words. The total memory density of the module is determined by the depth and width.
The number of ranks on a module is determined by the configuration and density of the component. In contrast, in an emerging DDR3 memory market, there are already six quad-rank modules in development. However, DRAM and module vendors have been able to develop several stacking technologies to further increase memory capacity on any particular memory module.
Figure 7. Stacked packaging using a flex circuit and PCB interposer For improved manufacturing reliability, die stack packages is another alternative to stacking DRAMs. This technology enables up to two dual or four quad die in one chip package. A couple of die stack packaging technologies shown in Figure 8 where the use of a window chip scaled package with an interposer and both die facing opposite directions or wire bonding to both die in the same direction.
In theory, a quad-die chip would maximize the number of DRAM die from 36 to on a single memory module. However, due to electrical limitations, the maximum achievable is 72 for now.
Figure 8. The dual-rank module only requires two chip-select signals while quad-rank would require four, one for each rank. Low Power DDR Technology As datacenters and server farms increase their capacity to meet higher bandwidth demand coupled with increasing DDR memory interface data rates, overall power consumption becomes more of a concern as companies grapple with rising energy costs.
The importance of energy saving solutions is beginning to take precedence. The DDR market is currently addressing the need for low-power, cost-saving solutions. As previously mentioned, the DDR2 technology operates at 1. A similar trend is beginning to develop in DDR3 where the original standard operating voltage is 1. Figure 10 shows a linear downward trend of the operating voltage for the DDR technology.
Going from 1.
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