Stub Series Terminated Logic


Stub Series Terminated Logic is a group of electrical standards for driving transmission lines commonly used with DRAM based DDR memory IC's and memory modules. SSTL is primarily designed for driving the DDR (double-data-rate) SDRAM modules used in computer memory; however, it is also used in other applications, notably some PCI Express PHYs and other high-speed devices.
Four voltage levels for SSTL are defined:
  • SSTL_3, 3.3 V, defined in EIA/JESD8-8 1996
  • SSTL_2, 2.5 V, defined in EIA/JESD8-9B 2002 used in DDR among other things.
  • SSTL_18, 1.8 V, defined in EIA/JESD8-15A, used in DDR2 among other things.
  • SSTL_15, 1.5 V, used in DDR3 among other things.
SSTL_3 uses a reference of 0.45 * VDDQ. SSTL_2 and SSTL_18 reference a voltage that is exactly VDDQ / 2.
SSTL_3 and SSTL_2 support two termination classes. SSTL_18 only supports one.