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AD9629: nonlinear and missing codes in convert output

Question asked by 朱煦然 on Mar 17, 2016
Latest reply on Apr 18, 2016 by DougI

Hi all,

 

I used reference circuit of AD9629 (also CN0272) to make a PCB. When I use stm32 to get the convert results, I get the following two strange figures.

捕获.JPG

Vertical ordinate is voltage. Horizontal ordinate is time. The green triangle curve is obtained by ADC of stm32 board. While the blue star curve is obtained by my AD9629 PCB. They worked on the same sinus signal at the same time.

 

The gray 'x' curve is obtained by saw tooth wave (not relate with time).

捕获1.JPG

This is the test result of two different AD9629 PCB with same circuit and architectures (a little difference to reduce the noise in board2).

 

In these two figures, the convertor is nonlinear and at the specific point it changed like some missing codes happened.

 

The power supply, differential input voltage, output circuit are all good. I have no idea about what is wrong except the convert result. Can anyone give me some advices or if you need more statistics about the board?

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