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SN65HVD1791:Attenuation of twisted pair line

Part Number: SN65HVD1791







  • Hi Miyauchi,

    Question 1: Twisted pair The graph on page 8 of the damping and frequency theoretical equation in shows the characteristics of "attenuation versus frequency". If you have a theory, please let me know. (Measurements from other cable manufacturers generally match this graph. The cable manufacturer did not know the theory.)

    Response 1: The app note does not include the exact equation for the graph in figure 3. General rule of thumb is that a cable will attenuate signal voltage -6db at max signaling rate in Hz. Attenuation specifications should be supplied by the cable manufacturer, as attenuation equations for a certain type of cable depends on many properties of the cable. 

    Question 2: What is the equivalent circuit for attenuation?

    Response 2: I believe what your looking for might be defined in transmission line theory with the Telegrapher's Equations. You can model a cable/transmission line with resistance of the conductor, self/mutual inductance - inductance of the conductor, capacitance between the inductors, and conductance of the dielectrically between signal + return lines. All of these parameters are represented by unit length of cabling. 

    Here is an equivalent circuit from one of our published app notes about data transmission line theory:

    Where R, L, C, and G are resistance/unit length, inductance/unit length, capacitance/unit length, and conductance/unit length. 

    Question 3: What is the relationship between attenuation, characteristic impedance, termination resistance, and damping resistance and damping resistance? (If you know question 2, you may be able to calculate it. What is the final signal voltage formula between the receiver voltage and the output signal voltage?

    Response 3: TI offers a very informative 3-part series about transmission line theory that will answer your question about most of these parameters. I have included a link for each of them below.



  • Hellow Tyler-san

    Thanks for your replay.
    I will study the information you gave me.
    If there is anything unclear, please let me ask you again.

    best regards