Reply
Posts: 4
Registered: ‎07-19-2017

The Vpp of oscillator SI5xx (3.3V, 50MHz) became larger with wire length

I mean the Vpp became larger and larger if lengthen the wire connect to output port of oscillator Si5xx, which watched by 350MHz oscilloscope.

is it normal?

Posts: 471
Registered: ‎01-18-2004

Re: The Vpp of oscillator SI5xx (3.3V, 50MHz) became larger with wire length


Teemo wrote:

I mean the Vpp became larger and larger if lengthen the wire connect to output port of oscillator Si5xx, which watched by 350MHz oscilloscope.

is it normal?


What output format did you choose?

Is a load attached to the output if it's configured as LVDS?

How long is the ground lead on your probe?

Posts: 4
Registered: ‎07-19-2017

Re: The Vpp of oscillator SI5xx (3.3V, 50MHz) became larger with wire length

Using LVCOMS oscillator Si501 to drive 2 chips for Ethernet function, it is OK.

But if connect another long wire to the output port of oscillator, the Ethernet ping  failure, and the Vpp became larger and larger if lengthen the wire.

Posts: 471
Registered: ‎01-18-2004

Re: The Vpp of oscillator SI5xx (3.3V, 50MHz) became larger with wire length

You can't just add a "long wire" and expect it to work. That "long wire" is an unterminated transmission line, and the reflections are killing you.
Posts: 4
Registered: ‎07-19-2017

Re: The Vpp of oscillator SI5xx (3.3V, 50MHz) became larger with wire length

Thanks for your information! 

Probably the test point for CLK(50MHz) is too far away from the output of oscillator in my PCB design (like a "long wire"). and it brings lots of reflections.