problems with ad9283

Hello,

I am using 2 AD9283 in my board.

One of them is working fine.

In other i have some peculiar problem.

Whatever might be the input, D6 to D0 are always identical and D7 always inverse to it.

This happens even if the input pins are detached from PCB pad. (Hence the input is only noise).

Sampling frequency is 45 MHz.

Please let me know why this happens.

Are there any problems with board layout?

Is it picking up some stray clock signals?..

Thanks and Regards,

Ajith

  • 0
    •  Analog Employees 
    on May 24, 2012 12:27 AM

    Hi Ajith,

    The ADC output code should reflect the digitized Voltage difference between the two Analog Input pins. The (1000 0000/0111 1111) output coding you describe represents normal "midscale" output code behavior when AIN = /AIN as detailed in datasheet Table 1. It sounds like your AIN signal on the problematic channel might not be making it all the way to the AD9283, or your Ain signals are somehow shorted to the same voltage level?

    This would explain why you see no difference in the output coding when you remove/lift the Ain input pins since this also results in essentially 0V differential (just low level noise delta) across the Ains.

    To debug you will need to verify that your differential Ain signals are actually being applied to the ADC's AIN and /AIN pins using a scope. It's also a good idea to probe the ENCODE, Supply, PWRDWN, and REF pins to make sure they are connected and driven properly. It sounds like you at least have a known good channel to compare to...

    Are you operating with a differential, or Single-Ended AIN config? I will be happy to review your schematic offline via email if you'd like. Just let me know.

    Best Regards,

    Tony M

  • Hello Tony,

    Thank you for the reply.

    I am operating in differential configuration.

    I will once again test thoroughly by comparing with the correct ADC and will let you know the results.

    Thanks and Regards,

    Ajith

  • Hello Tony,

    The cause for the behavior was, the voltage levels at the input were not high enough. With the gain increased  the faulty ADC is working fine.

    Once again thanks for your previous reply, it was very helpful.

    Regards,

    Ajith