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LMK00306 - LVDS AC coupling termination method

Kawai
Guru 19775 points
Other Parts Discussed in Thread: LMK00306

Hi Team,

Could you please allow me to clarify about the LVDS AC coupling termination method for LMK00306, which figure were changed in the LMK00306 latest datasheet ?

[Question1]
I believe LMK00306 could also use the following general AC coupling method.
Am I correct ? If there would be any problem, could you please let me know ?

[Question2]
The two examples for LVDS AC termination in the latest datasheet had 100ohm termination between the LVDS driver and AC coupling cap, please see below Figure 34. What is the advantage to do this instead of above construction ?

If LVDS Receiver has internal 100ohm termination and bias voltage, I thought it would only require AC cap.
If LVDS Receiver does not have internal termination and bias voltage, I thought above figure 3 would be good enough.

Best Regards,
Kawai

  • 0
    TI__Mastermind 32575 points

    The LVDS driver mode of LMK0030x device needs a DC current path between Out_P and Out_N to insure proper output DC biasing and avoid in-phase clock waveforms upon output startup.  This DC current path is normally provided by a DC coupled 100 ohm line termination. If the 100 ohm line termination must come after the AC coupling caps (e.g. internal termination in receiver device), it is possible to use a 1kohm resistor near the driver before the coupling caps to provide the necessary output DC current path while avoiding double 100 ohm termination (at both source and load in Fig. 34b, which reduces output swing by half). The 1k resistor will appear as high impedance before the transmission line and will not affect the 100 ohm line termination at the load, so the full output swing can be achieved at the receiver inputs.

    Regards,

    Alan

  • 0 in reply to Alan O
    Guru 19775 points

    Hi Alan-san,

    Thanks for the answer.

    Best Regards,

    Kawai