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  1. #1
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    impedance matching + transmission line

    Hi, I m designing an LVDS transmitter and during simulation I used a transmission line model under cadence environement' The transmitter contain two 50 ohm resistance forming 100 ohm differantial and for simulation I putted 100 ohm at the receiver level so that the transmission line sees from both sides 100 ohm, the simulation worked good but I don t understand why when I changed the 50ohm resistance by a series of 31 parallel resistance of 1.55 K ohm (this was for layout reasons) the impedance matching was destroyed and I noticed important reflection this is abnormal for me because the transmission line still see 100 ohm from both sides.
    Is there any one who can help me.
    Cordially.

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  2. #2
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    Re: impedance matching + transmission line

    It depends on the resistor. If you are simulating real 1.5K resistors with parasitic capacitance, they probably aren't true resistive at the LVDS operating frequency. For this reason, the solution may fail, at least in a real circuit. But you should know better about the parameters of simulated devices.



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