Dual data rate (DDR) sync SRAMs
High-speed memory technology combining double data rate (DDR) architecture with synchronous operation for improved data throughput.
DDR SRAMs are similar to the legacy synchronous burst SRAM products but with double data rate I/Os. Like the synchronous burst SRAMs, they are used for read-intensive functions such as packet lookup and packet classification in networking/communication applications. DDR SRAMs have a maximum clock speed of 550 MHz with a read latency of 1 cycle and are available in an industry-standard 165-ball BGA.
- Double data rate I/Os
- 550 MHz clock speed
- Industry-standard BGA
- On-die termination
Infineon's DDR SRAM portfolio
DDR-II CIO/SIO: DDR-II SIO SRAMs are similar to DDR-II CIO SRAMs but they include two separate ports: the read port and the write port to access the memory array. The read port has data outputs to support read operations and the write port has data inputs to support write operations. DDR II SIO SRAMs completely eliminate the need to "turn around" the data bus required with common I/O devices.
DDR-II+ CIO/SIO: DDR-II+ SRAMs are similar to DDR-II SRAMs in their operation but with additional performance improvements. The redundant data input clocks are not present in DDR-II+. Instead, DDR-II+ SRAMs include a handshake signal (QVLD) that indicates when the data will become valid thereby simplifying data capture. DDR-II+ SRAMs have a maximum speed of 550 MHz with read latencies of either 2 cycles or 2.5 cycles, with a burst length of 2 and are available in an industry-standard 165-ball BGA.
Improved signal quality at higher frequency
The ODT feature in the DDR-II+ family of devices improves the signal quality at high frequencies (greater than 300 MHz). High-frequency signals are susceptible to losses along transmission lines thereby causing signal distortion at the receiver. This will impact the receiver’s ability to interpret information correctly. In order for a transmission line to minimize the distortion of the signal, the impedance of every location on the transmission line should be uniform throughout its length. This can be achieved through either external resistors or on-die termination - embedded termination resistors within the die.
Advantages of on-die termination (ODT):
- Improves signal integrity by having the termination closer to the device inputs
- Simplifies board routing
- Saves board space by eliminating external resistors
- Reduces costs involved in using external termination resistors
