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I am using the AD9650.

In my board, the noise appears in the VIN± pin of the AD9650 when the analog to digital conversion starts.

The amplitude of the noise is about 200mVp-p.

The noise is a square wave, and the same cycle as the sampling clock of the ADC.

I tested change the ratio of dividing frequency of the sampling clock.
Then, the cycle of the noise changed similarly, too.

I removed the circuit connected with VIN± pin.
I measured the VIN± pin in the state.

The noise appeared though the VIN± pin was non connection.

I think that the circuit connected with the AIN± pin is not a cause.

I want to find the cause that the sampling clock does leaks to the AIN± pin.

Please give me some advice about the cause.

Best Regards,