LPDDR (Low Power Double Data Rate) SDRAM, a type of DDR SDRAM, also known as mDDR (Mobile DDR SDRAM), is a communication standard developed by the JEDEC Solid State Technology Association for low-power memory. Known for low power consumption and small size, it is specially used for mobile electronic products.
LPDDR4X DRAM: Performance and Power Efficiency Improvements Over LPDDR4
Ⅰ Overview of DDR and LPDDR
1. DDR
Double data rate synchronous dynamic random access memory (DDR SDRAM) or DRAM has become a real technology because it uses capacitors as storage elements to achieve various advantages such as high density and simple architecture, low latency, and high performance, almost unlimited access endurance, and low power consumption. DDR DRAM can be used in different forms according to system requirements-on dual in-line memory modules (DIMMs) or as discrete DRAM solutions. DDR is divided into three main categories, each with unique features that can help designers meet the power, performance, and area requirements of their target system-on-chip (SoC).
(1) Standard DDR is for servers, cloud computing, networking, notebook computers, desktops, and consumer applications. It supports wider channel widths, higher densities, and different shapes and sizes. DDR4 is currently the most commonly used standard in this category, supporting data rates up to 3200 Mbps. DDR5 DRAM runs at a speed of up to 6400 Mbps and has come out this year in 2020.
(2) Mobile DDR (LPDDR) is suitable for mobile and automotive applications that are very sensitive to area and power consumption. LPDDR provides a narrower channel width and several low-power operating states. LPDDR4 and LPDDR4X support data rates up to 4267 Mbps and are common standards in this category. LPDDR5 DRAM with a maximum data rate of 6400 Mbps has come out earlier this year.
(3) Graphics DDR (GDDR) is for data-intensive applications that require extremely high throughput, such as graphics-related applications, data center acceleration, and AI. GDDR and high bandwidth memory (HBM) are standards of this type.
Each standard is designed to provide high performance and capacity and minimize power consumption during operation. And the channel stability is improved through reliability, availability, and maintainability (RAS) and error correction code (ECC).
2. LPDDR
LPDDR DRAM
LPDDR DRAM provides a high-performance solution with significantly reduced power consumption, which is a key requirement for mobile applications such as tablets, smartphones, and automobiles. The SoC required for such applications tends to use fewer storage devices and shorter interconnections on each channel, and LPDDR DRAM runs faster than standard DDR DRAM (for example, LPDDR4/4X DRAM runs at a maximum speed of 4267 Mbps, while the operating speed of standard DDR4 DRAM is up to 3200 Mbps), so it can provide higher performance. However, LPDDR DRAM is not used in such devices. When in standby, they can be placed in a low-power state, such as a deep sleep state, or they can be operated at a lower frequency using the dynamic frequency scaling (DFS) function. Therefore, when the storage channel is on standby, the storage controller can use these low power consumption functions promptly to reduce the total power consumption.
Ⅱ Each generation of LPDDR
1.LPDDR2
The standard specification of the second-generation low-power memory technology LPDDR2 was officially released by the JEDEC Solid State Technology Association in December 2010. LPDDR2 is used in mobile products such as smartphones, cell phones, PDAs, GPS units, and portable game consoles. There are three main characteristics.
(1) Compared with the previous standard (LPDDR), the support of energy-saving technology has been increased. In terms of the interface (I/O) and internal voltage and internal voltage, the original LPDDR is +1.8V, but this time LPDDR2 also supports +1.2V. It also supports updating the “Partial Array Self Refresh” and “Per-Bank Refresh” of some memory arrays.
(2) Non-volatile memory (flash memory) and volatile memory (SDRAM) can share interfaces. This is the first time that flash memoryand SDRAM can share interfaces, which can reduce the pin count of the controller and increase the mounting density around the memory subsystem.
(3) Expanded the range of supported memory capacity and features. The supported operating frequency is 100MHz～533MHz. The data bit width is ×8, ×16, and ×32. There are 2bit and 4bit. Flash memory capacity is 64Mbit～32Gbit, DRAM is 64Mbit～8Gbit.
2.LPDDR3
The standard specification of the third-generation low-power memory technology LPDDR3 was officially released by the JEDEC Solid State Technology Association in May 2012. LPDDR3 also supports PoP stacked packaging and independent packaging to meet the needs of different types of mobile devices. The energy efficiency characteristics and signal interface of LPDDR2 have also been continued.
LPDDR3 also adds new technologies:
(1) Write-Leveling and CA Training: Allows the memory controller to compensate for signal deviations to ensure that the memory runs at the fastest input bus speed in the industry while maintaining data input settings, and the input timing of instructions and address.
(2) On Die Termination/ODT: Optional technology. It adds a lightweight terminator to the LPDDR3 data plane, improves high-speed signal transmission, and minimizes the impact on power consumption, system operation, and pin count.
3.LPDDR4
After the development of LPDDR2 and LPDDR3, LPDDR4 has begun to shine on mobile terminals such as smartphones and tablet computers, which has greatly improved the performance of smart products.
Since the data transmission speed of the input/output interface can reach up to 3200Mbps, which is twice the commonly used DDR3 DRAM, the newly introduced 8Gb LPDDR4 memory can support the shooting and playback of ultra-high-definition images, and can continuously shoot 20 million-pixel high-definition photos.
The capacity of LPDDR3 memory technology on mobile phones is generally 2G to 4G, while the bandwidth and frequency of LPDDR4 are twice that of LPDDR memory, and the maximum capacity of 8GB is supported, making daily-used smartphones have greater possibilities in functions and uses. The mobile phones that support LPDDR4 memory technology are represented by Iphone6s, Samsung s6, Samsung s7, and Huawei mate8.
Compared with LPDDR3 memory chips, LPDDR4 has an operating voltage drop of 1.1 volts, which is the lowest power storage solution suitable for large-screen smartphones and tablets, and high-performance network systems. Take the 2GB memory package as an example, compared with the 2GB memory package based on the 4Gb LPDDR3 chip, the 2GB memory package based on the 8Gb LPDDR4 chip can save up to 40% of power consumption due to the reduction in operating voltage and the increase in processing speed. At the same time, the input/output signal transmission of the new product uses Samsung’s unique Low Voltage Swing Terminated Logic (LVSTL), which not only further reduces the power consumption of the LPDDR4 chip, but also enables the chip to operate at low voltage. The high-frequency operation has realized the optimization of power supply efficiency.
The advent of LPDDR4X memory mainly solves the user’s problems with mobile phone power consumption. Its power supply voltage has dropped from 1.1v at DDR4 to 0.6v. This is a qualitative leap. Compared with LPDDR3 and LPDDR4, it saves power by 50% and 47% respectively.
4.LPDDR5
On February 20, 2019, JEDEC (Solid State Storage Association) officially released JESD209-5, the new low power memory standard for Low Power Double Data Rate 5 (LPDDR5). Compared with the first-generation LPDDR4 standard released in 2014, the I/O speed of LPDDR5 increased from 3200 MT/s to 6400 MT/s (DRAM speed 6400Mbps), which directly doubled. If it matches the common 64bit bus of high-end smartphones, it can transmit 51.2GB of data per second; if it is a PC’s 128bit BUS, it will break 100GB per second without pressure.
The Solid State Association believes that LPDDR5 is expected to greatly improve the performance of next-generation portable electronic devices (mobile phones, tablets). To achieve this improvement, the standard has redesigned the LPDDR5 architecture and shifted to the highest 16 Bank programmable and multi-clock architecture. At the same time, two commands to reduce data transfer operations are introduced, Data-Copy and Write-X, to reduce overall system power consumption. The former can directly copy the data of a single pin to other pins, and the latter reduces the power consumption when SoC and RAM transfer data. Besides, LPDDR5 also introduces link ECC error correction, the signal voltage is 250mV, and the Vddq/Vdd2 voltage is still 1.1V.
Compared with LP4x, LPDDR5 has reduced power consumption by more than 20% and has a deep sleep mode in terms of power consumption, as well as a dynamic scale application mode, which is very important for supporting core operation and power supply and can provide better services to end-users.
This means that the battery life of the end product will be extended. For example, compared to LPDDR4x, if LPDDR5 runs at a transmission speed of 5.5Gbps, the battery life of the mobile phone can be extended by 5%~10%. If it runs at the highest transmission rate of 6.4Gbps, the battery life of the mobile phone can be increased by more than 10%, which means it can achieve the all-day battery life.
LPDDR5 extends the battery life of mobile phones by 5%~10%
LPDDR5 DRAM uses dynamic voltage scaling (DVS) to save more power. At this time, the memory controller can reduce the frequency and voltage of DRAM during channel standby. Compared with ordinary standard DDR DRAM channels (64-bit wide), LPDDR DRAM channels are usually 16-bit or 32-bit wide. Like the other two categories of DRAM generations, each subsequent LPDDR generation (LPDDR5, LPDDR4/4X, LPDDR3, LPDDR2, LPDDR) has higher performance and lower power consumption than its predecessor. Also, any two generations of LPDDR are not compatible with each other.
Comparison of LPDDR generations
With the advent of 5G, LPDDR5 will also serve as its match. It is estimated that by the end of 2020, most mainstream flagship opportunities will have LPDDR5. From 2021 to 2022, mid-to-high-end 5G smartphones will be required to be equipped with LPDDR5. whether it depends on the number of mobile phones sold or the capacity sold, from 2022 to 2023, LPDDR5 will become the mainstream of the market.
LPDDR5 can realize today’s very advanced mobile phone applications, these applications often require very high bandwidth, exceeding the highest bandwidth LP4 can provide. For example, if you are using an LPDDR4 flagship mobile phone, the high-pixel camera inside will take several seconds to complete the processing and storage. If you use the LPDDR5, it will be a seamless process. If you run multiple apps at the same time, such as capturing videos, playing AI games, and sharing screens at the same time, troubles are likely to occur when using LPDDR4, but it is not a problem for LPDDR5.
5.LPDDR5X
Pushing the boundaries of chip development, Samsung has released its LPDDR5X DRAM chip for smartphones and other applications. The new chips bring higher speeds compared to the LPDDR5 standard, and it’s no surprise that we’ll see their use in several flagship phones in 2022.
LPDDR5X DRAM