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AD9826 cds mode not working when Vref from signal is used.

Question asked by jp021079 on Jul 30, 2018

Am trying to use AD9826 for CCD interface.

Configured register to 0x98 - input range 4V, CDS mode, and input clamp at 4V.

Confirmed through oscilloscope that CDSCLK1, CDSCLK2 and ADCCLK are provided at right intervals as per datasheet. After referring datasheet, understood that CDSCLK1 is provided to sense ref level from signal and CDSCLK2 for real signal. 

Problem is that, even though signal level varies, ADC output is always 65535. I have checked the CCD output it varies properly. When i enabled internal VRef, i found that ADC is providing output.

Please guide to find out, why is the ADC not providing output when Vref from signal is used?

Do let me know if more details are needed.