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Strange digital CMOS outputs of ADS5560

GangHan Lee
Prodigy 10 points
Other Parts Discussed in Thread: ADS5560

Hi,

I'm trying to get analog data using a Zynq7020 and a ADS5560 up to 20MSPS.

To test the system, I setup a function generator for input signal and a LDO DC power supply for ADC power. \

The ADS5560 is attached on a custom board with a MicroZed SOM.

First time, I got strange result like below. Thus I had purchased 5560EVM to compare it, but result is wrose than custom board.

I don't know where to start checking the system.

please advise me.

thanks in advance.

  • 0
    TI__Mastermind 29220 points

    Hi,

    not knowing any more than what you have described about the design, I would start with checking out the integrity of the digital interface from the ADC into the device you are using to catch the sample data.   The ADS5560 has the ability to output known data patterns, but you would have to use the SPI interface to program the SPI registers to make use of these features.   One simple test is to program a fixed pattern into the custom pattern registers, and then set the test pattern in address 0x65 to output the custom pattern.   I like to start with the pattern of all zero with a '1' in the least significant position and check the digital output.   Then I move the '1' to the 2nd least significant position and check the digital output.  And so on -- I 'walk' that single '1' through all 16 positions and see that my digital logic is receiving the right bits in the right places.    Then the most powerful test pattern is the arithmetic ramp, which is a simple counting pattern from all zero up through all one, and then wraps around back to zero and continues ramping up.   (the ramp pattern might only support 14 bits of ramp in this 16 bit device, from what I think I remember of it.)

    If the digital interface is operating correctly, then I would check the analog input to make sure that the input signal is fully differential and symmetrical about the VCM voltage, and that the common mode voltage of the input signal is within specifications.  (close to 1.5V.) 

    Regards,

    Richard P.