The Difference Between LPDDR4 and LPDDR5 Memory

Emerging and current applications, such as smartphones, tablets, autonomous systems, and IoT solutions, possess robust data volume growth. Adequate memory bandwidth is required to accommodate this data and to extract meaningful insights.  Massive computational power is also needed.  The Double Data Rate Synchronous Dynamic Random-Access Memory (DDR SDRAM or DRAM for short) is a favored choice of designers in all complex devices, due to its low latency, high bandwidth, and larger storage size. However, it requires additional specifications in embedded systems, such as low power, a wide temperature range, high reliability, and serviceability.

Advancements in DRAM from one generation of memory to the next have enabled higher performance levels. LPDDR4 and LPDDR5 are the two most recent Low Power (LP) DRAM generations in the market.  Both have advanced architectures, faster speeds, higher bandwidths, and lower power consumption. This Tech Spotlight highlights the benefits of DDR4 memory and its types, compares the DDR5 generation to its predecessor, and then delves into the impact and adoption trends of memory technology in the marketplace.

Basics of DRAM

One of the crucial aspects of any processing system is its ability to store large amounts of information in what we usually call "memory," or Random Access Memory (RAM) to be specific. It accommodates volatile information that can be accessed quickly and directly. Dynamic Random-Access Memory (DRAM) is the most common kind of random access memory (RAM) of choice for personal computers, smart devices, and workstations. DRAM is dynamic, unlike static RAM (SRAM), and can retain its contents only fleetingly (measured in milliseconds) and must be continually refreshed by reading its contents at short intervals. The memory stores each bit in a storage cell consisting of a capacitor and a MOSFET.

Synchronous DRAM (SDRAM), a type of DRAM, is a generic name for various kinds of DRAM synchronized with the optimized processor clock speed. It tends to multiply the number of instructions that the processor can perform at any given time. With improvements in processor speeds, DRAM memory has evolved into high-performance chipsets called DDR Synchronous Dynamic RAM. It nearly doubles the bandwidth of a single data rate (SDR) SDRAM running at the same clock frequency, employing a "double pumping" method. This technique allows data transfer on both the rising and falling edges of the clock signal without any increase in clock frequency.

DDR DRAM first arrived on the scene as a high-performance, low-cost memory solution targeted primarily at the personal computer and other cost-sensitive consumer markets. DDR has become globally popular over the last few decades, due to its low latency, low cost, and straightforward architecture. It has been used extensively in notebooks, laptops, gaming devices, and embedded computing systems. DDR DRAM memories are widely used in high-speed, memory-demanding applications, such as graphic cards, where there is a requirement to synthesize large amounts of information quickly. Servers, or single-purpose boards, powered by a single, more efficient power supply also need fast memory access, which DDR memories can accomplish. LPDRAM (Low-power DRAM) is specially used in consoles and many other mobile/portable devices due to its small size, low-power consumption, and cost-effectiveness.

The DDR series available in the market is characterized by each DDR manifesting new features and increased memory density. DDR1 SDRAM was succeeded by DDR2, DDR3, DDR4, and most recently, DDR5 SDRAM. Although they operate on identical principles, the modules in these generations are not backwards-compatible. Each generation delivers higher transfer rates and faster performance. Let's have a look at the types of DDR memories available across a generation.

DDR RAM Evolution

Figure 1. Generation of DDR memory
(Source: Micron)

First generation – DDR SDRAM

DDR SDRAM prefetch buffer size is 2n (two data words per memory access), double SDR SDRAM's prefetch buffer size. Prefetch, by way of review, allows a single address request to result in multiple data words. The internal clock speed of 133 ~ 200MHz gave the transfer rate of DDR1 as 266 to 400 MT/s (Million transfer per second). The DDR1 ICs were commercially released in 1998.

Second-generation – DDR2 SDRAM

DDR2 operates with an external data bus twice as fast as DDR1 SDRAM. The improved bus signal is responsible for such an achievement. The prefetch buffer of DDR2 is 4-bit, which is double that of DDR SDRAM. DDR2 memory has the same internal clock speed (133 ~ 200 MHz) as DDR memory. However, DDR2 memory has an improved transfer rate (533 ~ 800 MT/s) and I/O bus signal. DDR2-533 and DDR2-800 memory types were commercially released in 2003.

Third-generation – DDR3 SDRAM

DDR3 operates at the double the speed of DDR2. Further improvements in the bus signal allow such achievements. DDR3's prefetch buffer width is 8-bit, which is double that of DDR2. The transfer rate of DDR3 is 800 ~ 1600 MT/s. DDR3 operates at a low voltage of 1.5V compared with DDR2's 1.8V, which results in 40% less power consumption. The DDR3 ICs were commercially released in 2007.

Fourth-generation – DDR4 SDRAM

DDR4 kept the prefetch buffer size the same as DDR3, but achieved even higher speed and efficiency by sending more read / write commands per second. DDR4 standard divides the DRAM banks into two or four selectable bank groups, where transfers to different bank groups can be done faster. The operating voltage of DDR4 is reduced to 1.2 V compared to DDR3.  The transfer rate of DDR4 is 2133 ~ 3200MT/s. DDR4 ICs were commercially released in 2014.

Fifth-generation – DDR5 SDRAM

DDR5 SDRAM, commercially released in 2020, achieves higher speed by using a 16n prefetch buffer. DDR5 supports memory density from 8 GB to 64 GB, combined with a wide range of data rates from 3200 MT/s to 6400 MT/s.  The operating voltage of DDR5 is further reduced from 1.2V of DDR4 to 1.1V, approximately 8% lower than DDR4.  This memory enables what contemporary data centers need: increased reliability, availability, and serviceability (RAS).

DDR4 and LPDDR4 Memory

The increasing adoption of microcontroller and memory ICs in automobile electronics, and the growing application of memory storage chips in electronic devices, are significant factors pushing DDR4 DRAM products' demand. Further, the desire for consumer electronics led to DDR4 being a noted low-cost and high-performance option. The two key improvements in DDR4 are power consumption and data transfer speed, due to the development of an all-new bus. The memory supports a new, deep power-down mode that allows the host device to go into standby without the need to refresh its memory, and reduces standby power consumption by 40 to 50 percent.  Reduced power draw translates into less heat and longer battery life. Laptops and servers thus became the biggest beneficiaries of the jump to DDR4. Finally, DDR4 uses many higher-density chips, so each memory stick (DIMM, technically) packs a lot more memory.

Table 1: Comparative analysis of DDR4 and LPDDR4 memory (Source: Micron)

LPDDR4 (Low Power DDR4) is the mobile equivalent of DDR4 memory. Compared to DDR4, it offers reduced power consumption but does so at the cost of bandwidth. LPDDR4 has dual 16-bit channels resulting in a 32-bit total bus. To compare, DDR4 has an 8-word prefetch or a 64-bit channel. Therefore, LPDDR4 RAM halves the bus but makes up for this with a nominal operating voltage of 1.1-1.2V to save energy.

LPDDR4 was designed to increase memory speed in mobile computing devices such as smartphones, tablets, ultra-thin notebooks, and SBCs such as the Raspberry Pi. Micron has been leading the definition of LPDDR4, and its subsequent adoption, working towards satisfying consumer demands for faster boot and loading times while conforming to the platform's tight power constraints. Micron's LPDDR4 RAM tops out the standard with a 2133 MHz clock for a transfer rate of 4266 MT/s.

DDR5 and LPDDR5 – More Than a Mere Upgrade

DDR5, the successor of DDR4, was developed to deliver performance improvements when system designers felt rising pressure from continuous technological advancements—the memory bandwidth being unable to keep pace with newer processor models with escalated core counts. While previous generations focused on reducing power consumption and were driven by mobile and server applications, DDR5's primary driver was the need for more bandwidth. Compared to DDR4 at an equivalent data rate of 3200 mega transfers per second (MT/s), a DDR5 system-level simulation example indicates an approximate performance increase of 1.36X effective bandwidth. The approximate performance of DDR5-4800, at a higher data rate, increases to 1.87X—nearly double the bandwidth as compared to DDR4-3200. Micron's DDR5, driven by data rates up to 6400 MT/s and key architectural improvements, pushes potential system bandwidth even higher.

Figure 2:  Effective Bandwidth Comparison: DDR4 vs. DDR5. (Source: Micron)

With DDR5 DIMMs, power management moves from the motherboard to the DIMM itself. The DDR5 DIMMs have their voltage regulators, and 12V power management integrated circuits (PMICs) allow better granularity of system power loading and assists with signal integrity and noise issues. The DDR5 architecture increases the value that Micron brings to the industry with DRAM solutions. Significant performance improvements, made possible in part by increasing bank groups, burst lengths, and same bank refresh, help meet the stringent requirements of next-generation systems and improve the total cost of ownership. The system RAS is improved with the DDR5 on-die error correction code and post-package repair enhancement. Finally, the implementation of memory management is simplified with the use of the new multipurpose command feature.

While LPDDR4 remains mainstream in mobile and continues to progress in embedded applications, LPDDR5 is rapidly becoming the industry favorite in Low Power Volatile Memory. LPDDR5 offers the sweet spot of higher bandwidth, more compute power, and higher reliability at lower power consumption, perfect for embedded applications. The higher speed operation of LP5 tends to increase the data rate to 6.4 Gb/s up to 8.5 Gb/s vs. the LP4 top speed of 4266 Mb/s.

Conclusion: Who Benefits?

Data centers are addicted to the latest memory technology, as they must satisfy the constant demand for lower power requirements, higher density for more memory storage, and faster transfer speeds. Servers with DDR5 will work more efficiently and essentially squeeze more ROI out of the investment made in the server. Developers of cloud, enterprise, and artificial intelligence applications will benefit from DDR5 next-generation DIMMs, along with those involved in automotive, networking, and industrial use cases. While servers will drive initial demand for next-generation DDR, consumers will benefit too, as the technology will percolate into PCs and laptops. Several vendors have invested in DRAM's advancement to gain leverage in 5G technology and wireless communication.

The excitement continues to build around the possibilities that DDR5 will offer for computing systems in the coming months. Micron Technology has recently announced a comprehensive Technology Enablement Program (TEP) to aid in the design, development, and qualification of next-generation computing platforms utilizing DDR5 DRAM, the most advanced currently available.

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