ddr termination

September 29, 2020
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DDR Termination Regulators achieve power conservation by rapidly dropping or increasing current so that the output termination voltage (VTT) would be half of the supply voltage (VDDQ). Another reason why active DDR termination is important is for data integrity. Instead of having the necessary resistive termination located on the motherboard, the termination is located inside the semiconductor chips–technique called On-Die Termination (abbreviated to ODT). If there is any place in the line where the impedance is not uniform for some reason (open circuit, impedance discontinuity, different material) the signal gets modified by reflection at the impedance change point which results in distortion, ringing and so forth. The resistors can be combined to create a proper equivalent impedance value to the outside of the chip, whereby the signal line (transmission line) of the motherboard is being controlled by the on-die termination operation signal. In addition, on-die termination can reduce the number of resistor elements and complex wiring on the motherboard. This is described as "termination". Instead of having the necessary resistive termination located on the motherboard, the termination is located inside the semiconductor chips–technique called On-Die Termination (abbreviated to ODT).

Using the MAX1864 xDSL/cable-modem power supply, the circuit generates the termination voltage (VTT) which equals and tracks VREF. On-die termination is implemented with several combinations of resistors on the DRAM silicon along with other circuit trees. Although the termination resistors on the motherboard reduce some reflections on the signal lines, they are unable to prevent reflections resulting from the stub lines that connect to the components on the module card (e.g. DRAM component) will be reflected back onto the signal line, thereby introducing unwanted noise into the signal. Its maximum voltage deviation should not exceed 40mV during extreme load transients, from the maximum rated sinking current to … DRAM Module). DDR Termination Regulator General Description RT9026 is a 3A sink/source tracking termination regulator. The length of the DDR memory interconnects, coupled with the multiple stubs required for supporting dual inline memory modules (DIMS), results in signal reflection that can cause data corruption. DRAM circuit designers can use a combination of transistors which have different values of turn-on resistance.

In lower frequency (slow edge rate) applications, interconnection lines can be modelled as "lumped" circuits. In the case of DDR2, there are three kinds of internal resistors 150ohm, 75ohm and 50ohm. The internal on-die termination values in DDR3 are 120ohm, 60ohm, 40ohm and so forth. For example, resistors can be placed on computer motherboards to terminate high speed busses. The termination voltage supply for DDR memory needs to track the DDR memory supply voltage, VDDQ, and it needs to source and sink the load current. This problem has required more attention as speeds have increased. DDR termination regulators are an essential component to regulate power through DDR transmission lines. There are several ways of termination depending on how the resistors are connected to the transmission line. Parallel termination and series termination are examples of termination methodologies. The signal that propagates along the stub to the component (e.g. A signal propagating from the controller to the components encounters an impedance discontinuity at the stub leading to the components on the module. DDR Memory/Bus Termination Analog Device’s SRAM memory supplies and bus termination products are the ideal choice for DDR, QDR memory, SSTL logic, and HSTL interface for high-speed FPGAs and processors as well as other advanced portable microprocessor-based systems. In order for a transmission line to minimize distortion of the signal, the impedance of every location on the transmission line should be uniform throughout its length. On-die termination (ODT) is the technology where the termination resistor for impedance matching in transmission lines is located inside a semiconductor chip instead of on a printed circuit board (PCB). SSTL leverage s an active motherboard termination scheme and overcomes the signal integrity concerns with legacy LVTTL signaling. The RT9026 possesses a high speed operating amplifier that provides fast load transient response and only requires 20μF of ceramic output capacitance. However, if the propagation delay in a wire, PCB trace, cable, or connector is significant (for example, if the delay is greater than 1/6 of the rise time of the digital signal), the "lumped" circuit model is no longer valid and the interconnect has to be analyzed as a transmission line. Under the low frequency condition, every point in an interconnect wire can be assumed to have the same voltage as every other point for any instance in time. It is specifically designed for low-cost and low-external component count systems.

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