AD9629: nonlinear and missing codes in convert output

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.

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).

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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  • Hi Dougl,

    I have read the data sheet of AD9260, which said that the bias current is used by modulator amplifiers and flash preamplifiers. But I know AD9260 combined delta-sigma and pipeline and AD9629 only uses pipeline. So can you tell me more details about which amplifiers will use that bias current?

    Besides, I did some additional test about Rbias. The problem (discontinuity) only happens when Rbias = 70Kohms-100Kohms. But when it equals to 20kohms, 150kohms, 200kohms and 240ohms, the curves are just same with 10kohms(correct one). I can't understand this phenomenon.

    Do not apologize. It's my pleasure to get your help!

    朱煦然

Reply
  • Hi Dougl,

    I have read the data sheet of AD9260, which said that the bias current is used by modulator amplifiers and flash preamplifiers. But I know AD9260 combined delta-sigma and pipeline and AD9629 only uses pipeline. So can you tell me more details about which amplifiers will use that bias current?

    Besides, I did some additional test about Rbias. The problem (discontinuity) only happens when Rbias = 70Kohms-100Kohms. But when it equals to 20kohms, 150kohms, 200kohms and 240ohms, the curves are just same with 10kohms(correct one). I can't understand this phenomenon.

    Do not apologize. It's my pleasure to get your help!

    朱煦然

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