Anyone ever heard about double reflection?

[henrytqy]

Hi dear all,

Recently, I was desgning a broadband driver. One of the paper said "In broadband applications, the buffer must drive an on chip back termination resistor of about 75 ohm in addition to an off chip load of 50 ohm in order to reduce the double reflections"

Anyone know this conception? Why 75/50 can reduce it?

Thanks~~~

 

[BabaYaga]

Can you give further details like what driver you are using and what is that paper that you are talking about, from what you have given i feel that the dual termination that you are talking about is much similar to the DDR3 dual termination.

In DDR3, For optimum signaling, a typical dual-slot system will have a module terminate to a LOW impedance value (30Ωor 40Ω) when in an idle condition. When the module is being accessed during a WRITE operation, greater termination impedance is needed, for example, 60Ωor 120Ω. Dynamic ODT(On Die Termination or on chip termination) enables the DRAM to switch between HIGH or LOW termination impedance. This is advantageous because it improves bus scheduling and decreases bus idle time and also this improves Signal Integrity by reducing reflections and overshoot and undershoot.

I hope this helps. but for a clearer picture please provide more details.