LMK03318: Could we select register to control rise time ?

Hi Shu-Cheng,

There are no registers to adjust slew rate except for on the STATUS[1:0] LVCMOS outputs, which can be adjusted by setting R49. V_min also cannot be adjusted by register controls. However, the differential output drivers should already have a rise/fall time of under 300ps (20-80%).

From the scope screenshot it looks like there are reflections which are affecting the signal integrity and causing the scope to not properly measure the rise time. Could you double check the output termination scheme? See section 10.4.16: 'High-Speed Clock Outputs' on page 44 of the datasheet for example output termination schemes. I see that the scope input shows 50ohm termination- note that unless it can be set to Hi-Z or a high impedance probe is used, the scope will act as a 50ohm resistor. If you have a schematic of the output termination scheme I can also double-check that.

Also, when using AC coupling, the receiver DC bias can be adjusted. How this can be done depends on the receiver. Some receivers may have built in biasing capability, or resistor networks can be used to set the DC bias accordingly.

Regards,
-Tim