AD9629 Read


I am new to reading ADC. I want to use AD9629 in my design. And i want to read this with FPGA. How can i handle it? Where should i start when writing the VHDL code? What are the things i should be aware of?

Best regards.

Parents Reply
  • Hi Doug,

    I am trying to read AD9629 and i want to ask some questions. 

    This is my circuit. Analog input range(Pin-9) of AD8475 is 0 to 4.2V. ADC inputs become 0.46V and 1.34V when AD8475 input is 0.29. And digital output of the ADC is 8D5. This value is true?

    What should be the relationship between input values and output? 

    I can't understand this table. What is the meaning of this?

    Thanks for help.

  • 0
    •  Analog Employees 
    on Apr 28, 2020 1:44 AM in reply to hrnttk

    Hi HrnTtk,

    To verify you capture the ADC outputs properly, I recommend that you use the output test patterns controlled by Register 0x0D Bits[3:0]. For example, to output a checkerboard pattern you would do the following SPI writes:

    Write Register 0x0D = 0x04
    Write Register 0xFF = 0x01

    This will put AD9629 in output checkerboard test mode. There are several other test patterns to choose from. Please see Table 16 in the AD9629 datasheet for more options.

    Table 12 in the AD9629 datasheet shows the output values for a few selected voltage values at the analog input. I numbered them in the picture above to match the numbers in the description below.

    1. This shows the value when the differential voltage at the ADC inputs are less than the negative full scale value. This means that the VIN+ - VIN- is less than 1V by more than 0.5LSB. The output is a minimum code and the MODE/OR pin goes high, if the MODE/OR pin is in OR mode.
    2. This is when the differential input voltage is right at the negative full-scale value (VIN+ - VIN- = 1V). The ADC outputs the minimum code. OR does not go high.
    3. This is with VIN+ = VIN-. When the voltage on each input are equal to each other, the differential input voltage is zero. In this case the ADC outputs a mid-scale code.
    4. This is with the differential input voltage at full-scale. The ADC outputs a maximum code value.
    5. This is with the differential input voltage above full-scale. The ADC outputs a maximum code value and the OR pin goes high, if the MODE/OR pin is in OR mode.

    Does this answer your question?

    Thank you.


  • Hi Doug,

    In offset binary mode and second condition(Vin+ - Vin- = -1V), i am reading 800H. I check the DFS pin and it is logic zero. So the output mode of ADC is offset binary. But it gave an output according to the 2's comp. mode in second condition. What can be the problem?

    Best regards.


  • 0
    •  Analog Employees 
    on May 5, 2020 7:16 PM in reply to hrnttk

    Hi Harun,

    Is your CSB pin connected to DRVDD to put the AD9629 in "pin mode" (non-SPI mode)?

    Thank you.


  • Yes, my CSB pin connected to DRVDD.

    Thank you.

  • Hi Doug,

    I am sending some values that i saved.

    Vin+ - Vin-              ADC Output

    -1V                              800

    -0.28V                         DA9

    0V                               807

    0.32V                          AB4

    0.68V                          D75

    1V                               FFF

    According to my results, the ADC does not work properly when the Vin+ - Vin- value goes to negative. 

    And also my DCO signal is not exactly a square wave, it is a sinusoidal wave. Could this be the source of the problem?