QPCIe local oscillator

[shao]

I want to do some phase alignment measurement using 4 receiving channel on the QPCIe board.

I have read its datasheet but got a bit confused.

Why the 30.72MHz is labeled as XO2 or XO3? Aren’t they referring to the same oscillator?

And there is another oscillator of 40MHz as XO4, when is that used?

My goal is to use all 4 receiving channel with the same LO, do I need to do some configuration on LimeSuiteGUI?

Here’s the photo of those oscillators on the real hardware.

[Zack]

Hi @shao,

@shao

Why the 30.72MHz is labeled as XO2 or XO3? Aren’t they referring to the same oscillator?

These are two different oscillators, but fit to the same physical space on the board. Hence you may have only one soldered at the same time.

@shao

And there is another oscillator of 40MHz as XO4, when is that used?

When you need 40MHz reference clock.
Actually, only XO1 is active by default configuration. There is section 2.2.8.2 in the same document which explains what you have to change in order to get other XOs activated.

@shao

My goal is to use all 4 receiving channel with the same LO, do I need to do some configuration on LimeSuiteGUI?

Reference clock for both LMS7002M chips is the same and it is XO1. That means that all 4 channels are referenced by the same reference clock.

[shao]

Thanks. That is of great help!