Shulou(Shulou.com)06/02 Report--

DDR SDRAM is a SDRAM with double data transfer rate, and its data transmission speed is twice that of the system clock frequency. Due to the increase in speed, its transmission performance is better than that of the traditional SDRAM. DDR SDRAM can transmit data at both the rising edge and falling edge of the system clock. SDRAM only transmits data once in a clock cycle, it transmits data during the rising period of the clock, while DDR transmits data twice in a clock cycle, that is, it transmits data once in the rising period and falling period of the clock. The following is Yingshang Microelectronics to introduce the development of DDR SDRAM memory.

(1) DDR SDRAM

DDR SDRAM double data rate synchronous dynamic random access memory is an upgraded version of SDR SDRAM. DDR SDRAM transmits signals once at the rising edge and falling edge of the clock cycle, so that its data transmission speed is twice as fast as SDR SDRAM, and this does not increase power consumption. As for the addressing and control signals are the same as SDR SDRAM, only transmitted at the rising edge, this is a tradeoff between the compatibility and performance of the memory controller at that time.

The DDR SDRAM uses 184pin's DIMM slot, which changes from two to one in SDR SDRAM. The common operating voltage is 2.5v. The frequency of the original DDR memory is 200MHz, and then DDR-266, DDR-333 and the mainstream DDR-400 of that era are slowly born. As for those running in 500MHz, 600MHz and 700MHz are all regarded as overfrequency stripes. When the DDR memory just came out, there was only a single channel, and then there was a support for double-pass chipsets. By doubling the bandwidth of memory directly, two pieces of DDR-400 memory can basically meet FBS 800MHz's Pentium 4 processor, with the capacity from 128MB to 1GB.

(2) DDR2SDRAM DDR2/DDR II SDRAM is a new generation of memory technology standard developed by JEDEC. The biggest difference between DDR2SDRAM and the previous generation of DDR memory technology standard is that although it uses the basic way of data transmission at the rising / falling edge of the clock at the same time, DDR2SDRAM memory has twice the pre-read ability of the previous generation of 4bit memory (i.e. 4bit data read prefetch). In other words, DDR2 memory each clock can read / write data at four times the speed of the external bus and run at four times the speed of the internal control bus.

The standard voltage of DDR2 drops to 1.8V, which makes it more energy-efficient than the previous generation. The frequency of DDR2 ranges from 400MHz to 1200MHz. At that time, the mainstream is DDR2-800. the higher frequency is actually super-stripe, and the capacity starts from 256MB to the largest 4GB, but the DDR2 of 4GB is very little. at the end of the DDR2 era, it is mostly the capacity of a single 2GB.

(3) DDR3 SDRAM DDR3 provides higher operating efficiency and lower voltage than DDR2 SDRAM, which is the successor of DDR2 SDRAM (increased to eight times), and is also a popular memory product specification.

Compared with the previous generation of DDR2, DDR3 has made new specifications in many aspects, the core voltage is reduced to 1.5V, and prefetching has changed from 4-bit to 8-bit, which is also the key for DDR3 to improve bandwidth. The same core frequency DDR3 can provide twice as much bandwidth as DDR2. In addition, DDR3 also adds CWD, Reset, ZQ, STR, RASR and other technologies.

DDR3 memory is the same as DDR2 240Pin DIMM interface, but the location of the two anti-gap is different, can not be mixed, the common capacity is 512MB to 8GB, of course, there is a single 16GB DDR3 memory, but very rare. The frequency aspect starts from 800MHz, at present compares the capacity to buy the highest frequency 2400MHz, in fact some manufacturers have launched the 3100MHz DDR3 memory, but is more difficult to buy, the platform that supports DDR3 memory has Intel's later LGA 775 motherboard P35, P45, x38, x48, LGA 1366 platform, LGA 115x series all support and LGA 2011 x79 AMD aspects of AM3, AM3+, FM1, FM2, FM3 interface products all support DDR3.

(4) from DDR to DDR3 in DDR4 SDRAM, the number of memory prefetching bits in each generation of DDR technology doubles, and the first three are 2bit, 4bit and 8bit, respectively, in order to achieve the goal of doubling memory bandwidth. However, DDR4 maintains DDR3's 8bit design on prefetching bits, because it is too difficult to continue doubling to 16bit prefetching, DDR4 increases the number of Bank instead, it uses Bank Group (BG) design, 4 Bank as a BG group, free to use 2-4 groups of BG. Each BG can be operated independently. If 2 sets of BG are used, the data of 16 bits per operation and 4 groups of BG can achieve 32bit operation, which actually increases the prefetch bit width in disguise.

There are three biggest differences between DDR4 and DDR3: 16bit prefetching mechanism (DDR3 is 8bit), the theoretical speed under the same kernel frequency is twice as fast as DDR3; more reliable transmission specifications further improve data reliability; the working voltage drop to 1.2V, more energy-saving.

The number of pins in DDR4 memory has increased from 240s in DDR3 to 284. the position of the gap is also different from that of DDR3. Another change is that the gold finger of DDR4 is high in the middle and has a slight curve on both sides, while the gold finger of memory before is straight. DDR4 not only maintains a sufficient signal contact area with the DIMM slot, but also can remove memory more easily than DDR3.

For example, the 32-bit DDR4 SDRAM of UMI, the density of UMI UD408G5S1AF is 8Gb and the data rate is 3200Mbps/2933Mbps/2666Mbps/2400Mbps/2133Mbps/1866Mbps/1600Mbps. Commercial operating temperatures range from 0 ℃ to + 95 ℃ and industrial operating temperatures range from-40 ℃ to + 95 ℃. Support for applications in UltraScale FPGA devices helps ensure maximum timing margin. In order to ensure optimal signal integrity, Istroke O technology also includes transmission pre-emphasis, reception equalization, low jitter clock and noise isolation design technology. Yingshang Microelectronics supports DDR4SDRAM memory interface for sample delivery and testing.

Comparison of memory performance parameters of different types of DDR

From DDR to DDR4, the differences of different performance parameters are mainly reflected in two places: power supply voltage and data transmission rate. The value of power supply voltage is getting lower and lower, while the data transmission rate is increasing geometrically.

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