ADC3663: 82Khz oscillation frequency in input channel A and B

Hi Team,

They disconnected the THS4561 by desolder the 10Ohm resistor.

Still have oscillation here, I let them to measure the INP, diff clock, DclockIN, DCLK and FCLK, please check the waveform. I think the clock is good though.

INP:

DIFF CLOCK:

DCLKIN:

DCLK：

FCLK：

Thank you,

Yishan Chen

Hi Yishan,

Do they see this "oscillation" on both the AINP and AINM pins?

If so, this is to be expected probing these inputs with an oscope. 

The ADC is not buffered and will have kickback on the analog inputs from the sampling switch opening and closing.

Regards,

Rob

Hi Rob,

Oscillation also happened both on AINP/AINM, please check below waveform, if it is due to the switch, why the oscillation frequency is low.

AINP:

AINM:

Thank you,

Yishan Chen

Hi Yishan,

Are these two oscope plot with a good grounded probe?

You might just be seeing loop inductance of the probe.

Is this causing any issues on the ADC's output spectrum?

Can you send me a picture of an FFT or data capture? That might help.

Thanks,

Rob

Hi Rob，

They put the probe in INAP/M and 3663 ground.

What is your recommend way to measure the voltage in INP/M？

I don't think it will be the loop inductance. Because they use same way to measure the output of THS4561, they don't see the oscillation.

Thank you

Yishan Chen