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DS90LV011A: Characteristic impedance of each differential transmission line

Koshi Ninomiya
Expert 5435 points
Part Number: DS90LV011A
Other Parts Discussed in Thread: DS90LV012A

Tool/software:

Daer Team,

My customer uses the DS90LV011A (Driver) and the DS90LV012A (Receiver) for LVDS transmission.
There are three parts from the DS90LV011A to the DS90LV012A. The Power Board, the Board-to-Board Connector and the Control Board.
The characteristic impedance of each differential transmission line is total 100Ω, or each part is 100Ω?

Best Regards,

Koshi Ninomiya

  • +1
    TI__Genius 9616 points

    Hi Koshi, 

    The characteristic impedance (Zo) is a property of the entire transmission line that can describe any portion of it. Think of it like the thickness of a water pipe that has a constant flow rate. If you cut any portion of the pipe in half, the cross section will have the same thickness regardless of where you cut. If you have a section of the pipe that differs in thickness, there will be a disturbance in the flow rate of water (i.e. reflections). Same principle applies to transmission lines. The equivalent circuit model (with L, R, and C factored in) of any section of the transmission for LVDS should equal 100 Ohms, including the total termination resistance. This where the term "impedance matching" comes from, and it is to make sure there are no signal reflections. Since you only need to terminate at the receiver for a transmission line, this circuit only requires one 100Ohm resistor. If you want to know more about what factors into transmission line impedance, this app note has some illustrations and formulas to paint a clearer picture: AN-806 Data Transmission Lines and Their Characteristics (Rev. A) 

    Regards,

    Matt