About ADC

Hello,

I'm confused with this electric circuit which is signed out on the attachments,The circuit is made up by two parts:ADC driver(AD8138) & ADC(AD9214),Analog signal source come from pin5 of XS1,which is a continous analog signal.

My system is like this:the ture source is from a APD,then use three stage amplify the output of APD,then the analog signal go to pin5 of XS1.

The frequency of the sample clock(FPGA_CLK2) is 100MHz.

attachment<AD8138> is an image of circuit for AD8138;

attachment<AD9214> is an image of circuit for AD9214;

attachment<sheet_part> is a schematic diagram for AD8138 and AD9214 both,the schematic diagram is designed by Altium designer.

Would you please to give me some suggestions?

BR

Tom

attachments.zip
Parents
  • Hi Tony M,

    By the way,I want to ask another question about setting for pin2 of AD9214,there are four ways to configure this pin to archive four different functions,these configurations are signed out in datasheet of AD9214.

    These words is from your datasheet:

    Data Format Select and Gain Mode Select. Connect externally to AVDD for two’s complement

    data format and 1 V p-p analog input range. Connect externally to AGND for Offset Binary data

    format and 1 V p-p analog input range. Connect externally to REF (Pin 4) for two’s complement

    data format and 2 V p-p analog input range. Floating this pin will configure the device for Offset

    Binary data format and a 2 V p-p analog input range.

    But I can see another different configuration way is signed out in figure 10,I see that floating way is not used in figure 10,but the way of connecting a capacitance then directly tied to AGND is appeared.I used this way in my design and you can see it in document <AD9214.png>,by using a scope to test this pin's wave,I can see a 2.28V DC level component on it and this is not a clean DC signal(many noises on it) .I got 5 circuit board with the same condition and got two different testing results,I tested the ADC's output digital signals,one result is just a half of the other.then I tied pin2 of AD9214 to AGND directly,the results are not different anymore.I don't know why?

    Best Regards

    Tom

Reply
  • Hi Tony M,

    By the way,I want to ask another question about setting for pin2 of AD9214,there are four ways to configure this pin to archive four different functions,these configurations are signed out in datasheet of AD9214.

    These words is from your datasheet:

    Data Format Select and Gain Mode Select. Connect externally to AVDD for two’s complement

    data format and 1 V p-p analog input range. Connect externally to AGND for Offset Binary data

    format and 1 V p-p analog input range. Connect externally to REF (Pin 4) for two’s complement

    data format and 2 V p-p analog input range. Floating this pin will configure the device for Offset

    Binary data format and a 2 V p-p analog input range.

    But I can see another different configuration way is signed out in figure 10,I see that floating way is not used in figure 10,but the way of connecting a capacitance then directly tied to AGND is appeared.I used this way in my design and you can see it in document <AD9214.png>,by using a scope to test this pin's wave,I can see a 2.28V DC level component on it and this is not a clean DC signal(many noises on it) .I got 5 circuit board with the same condition and got two different testing results,I tested the ADC's output digital signals,one result is just a half of the other.then I tied pin2 of AD9214 to AGND directly,the results are not different anymore.I don't know why?

    Best Regards

    Tom

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