Embedded Design Handbook

ID 683689
Date 8/28/2023
Public
Document Table of Contents

3.5.5.5. SDRAM Types

There are a several types of SDRAM devices. The following types are the most common:

  • SDR SDRAM—Single data rate (SDR) SDRAM is the original type of SDRAM. It is referred to as SDRAM or as SDR SDRAM to distinguish it from newer, double data rate (DDR) types. The name single data rate refers to the fact that a maximum of one word of data can be transferred per clock cycle. SDR SDRAM is still in wide use, although newer types of DDR SDRAM are becoming more common.
  • DDR SDRAM—Double data rate (DDR) SDRAM is a newer type of SDRAM that supports higher data throughput by transferring a data word on both the rising and falling edge of the clock. DDR SDRAM uses 2.5 V SSTL signaling. The use of DDR SDRAM requires a custom memory controller.
  • DDR2 SDRAM—DDR2 SDRAM is a newer variation of standard DDR SDRAM memory which builds on the success of DDR by implementing slightly improved interface requirements such as lower power 1.8 V SSTL signaling and on-chip signal termination.
  • DDR3 SDRAM—DDR3 is another variant of DDR SDRAM which improves the potential bandwidth of the memory further by improving signal integrity and increasing clock frequencies.
  • QDR, QDR II, and QDR II+ SRAM—Quad Data Rate (QDR) SRAM has independent read and write ports that run concurrently at double data rate. QDR SRAM is true dual-port (although the address bus is still shared), which gives this memory a high bandwidth, allowing back-to-back transactions without the contention issues that can occur when using a single bidirectional data bus. Write and read operations share address ports.
  • RLDRAM II and RLDRAM 3—Reduced latency DRAM (RLDRAM) provides DRAM-based point-to-point memory devices designed for communications, imaging, server systems, networking, and cache applications requiring high density, high memory bandwidth, and low latency. The fast random access speeds in RLDRAM devices make them a viable alternative to SRAM devices at a lower cost.
  • LPDDR2—LPDDR2-S is a high-speed SDRAM device internally configured as a 4- or 8-bank memory. All LPDDR2 devices use double data rate architecture on the address and command bus to reduce the number of input pins in the system. The 10-bit address and command bus contains command, address, and bank/row buffer information. Each command uses one clock cycle, during which command information is transferred on both the positive and negative edges of the clock.
  • LPDDR3—LPDDR3-SDRAM is a high-speed synchronous DRAM device internally configured as an 8-bank memory. All LPDDR3 devices use double data rate architecture on the address and command bus to reduce the number of input pins in the system. The 10-bit address and command bus contains command, address, and bank buffer information. Each command uses one clock cycle, during which command information is transferred on both the positive and negative edges of the clock.

For more information about SDRAM types refer to the External Memory Interface Handbook Volume 2: Design Guidelines.