What is DDR termination voltage?

Double data rate (DDR) synchronous DRAM (SDRAM) is used in high-speed memory systems in workstations and servers. These memory ICs use 2.5V or 1.8V supply voltages. They require a reference voltage equal to half the supply voltage (VREF = VDD/2).

What is termination in DDR?

The goal when terminating Double Data Rate (DDR) memory signals is to maintain signal integrity. The board designer must properly terminate the signal lines and make efficient use of layout space to meet this goal.

What is VREF in DDR?

VREF is a low-power reference voltage equal to VDD/2. DDR devices compare internal signals to VREF. Other voltage relationships are VDD = VDDQ, and VTT = VREF = VDD/2. VTT transient current can be as high as ±3.5A during heavy activity on the DQ and address buses.

What is DDR signals?

In computing, a computer bus operating with double data rate (DDR) transfers data on both the rising and falling edges of the clock signal. This is also known as double pumped, dual-pumped, and double transition. The term toggle mode is used in the context of NAND flash memory.

How is the value of a termination resistor determined?

The basic rule when choosing a termination resistor is that the value of the resistor must equal the characteristic impedance of the twisted pair cable. Termination resistor prevents signal rebound, like waves hitting a wall.

Why are termination resistors used in differential pair signals?

In electronics, you’ll encounter termination resistors when you’re working with differential pair signals, such as the RS 485. It is a simple component that ensures signal integrity on the bus, especially when high-speed transmission is involved. Furthermore, termination resistors are used to avoid signal reflections.

What is the output impedance of a DDR3 DIMM?

To calibrate output driver impedance, an external precision resistor, RZQ, connects the ZQ pin and VSSQ. The value of this resistor must be 240-ohm ± 1%. If you are using a DDR3 SDRAM DIMM, RZQ is soldered on the DIMM so you do not need to layout your board to account for it. Output impedance is set during initialization.

How many signals are in a DDR memory controller?

The DDR memory controller consists of more than 130 signals and provides a glueless interface for the memory subsystem. These signals can be divided into the following signal groups for the purpose of this design guide: †Clocks †Data † Address/Command † Control † Feedback signals Table 1 depicts signal groupings for the DDR interface.