How to calculate AD9218's slope?

Hi guys,

We are using many AD9218BSTZ-105 chips, which are used on ADC daughter boards. Now, we are testing those ADC daughter boards performances. One of the important specification is slope. Our question about slope is how to calculate  (how to test it?) ADC's slope?

We are asking this qauestion becuase we tested it by input different DC values to ADC. For example: Input 0mV, 100mV, 200mV, 300mV, 400mV,500mV, 600mV,700mV,800mV,900mV and 1000mV into ADC channels respectively and get the sampling value. We collected 1000 samples at each constant DC value. Then we calculate this ADC's channel's slope according these collected sampling values.

We don't know if our method is correct or not? And how ADI calculate your ADC devices slope? We found that different ADC chips have different slopes. For example, sometimes is 0.97, sometimes 0.92, and sometime about 0.95, and so on. Is this ok when getting those slope ratio vary?

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  • Hello Mayott,

    I attached our ADC daughter board's schematic design.

    How to understand "This is a 10V part with a 2V input range, so an LSB is going to be ~2mV."? I remmenber AD9218's input range is 1V p-p. 

    You can find that we used AD8138 to drive AD9218 with DC coupling from attached file. Our slope testing include AD8138 and AD9218. Our final product is PET, so we need many ADC channels, and many front-end amplifiers.

    BTW, can you provide us your method of testing INL and DNL?

    ad9218_daughterboard_v3.pdf
Reply
  • Hello Mayott,

    I attached our ADC daughter board's schematic design.

    How to understand "This is a 10V part with a 2V input range, so an LSB is going to be ~2mV."? I remmenber AD9218's input range is 1V p-p. 

    You can find that we used AD8138 to drive AD9218 with DC coupling from attached file. Our slope testing include AD8138 and AD9218. Our final product is PET, so we need many ADC channels, and many front-end amplifiers.

    BTW, can you provide us your method of testing INL and DNL?

    ad9218_daughterboard_v3.pdf
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