I am using AD9283-100 operating at 50MHz. Ian using internal reference. I am always getting output code as all zeros. When I monitored the Vref at Pin 2 and Pin 3 shorted to ground I am getting 1.82V instead of specified 1.25V. what could be the reason.
Thanks for the additional info regarding your measurements. Please note the Analog Input Common Mode voltage is internally biased at a value of ~0.3 x VD, or 0.9V when operating from a nominal 3V supply. Please refer to datasheet figure 2 and the Analog Input Theory of operation on datasheet page 8. The Analog Input Common mode voltage is not directly influenced/biased from the fixed internal 1.25V VREF OUT voltage. The 1.25V VREF controls the Analog input full-scale span which by default is 1.024Vp-p.
You can think of the Analog Input Common Mode Voltage (~0.9V with a 3V supply) as the fixed midpoint with the Ain signal swinging +/-0.512V (1.024Vp-p) around this CM midpoint in single-ended (SE) Mode. For SE mode you will typically drive the AIN terminal with your 1.024Vp-p AC coupled signal, while leaving the AIN/ floating, or preferably connected through a 0.1uF cap and 25ohm series resistor to Ground. I'm attaching an Ain Voltage vs output coding table to help illustrate.
Please verify your supplies and decoupling nodes are properly configured. I will be happy to contact you offline via your EZone registration email if you would prefer to share your AD9283 schematic/layout outside of the public forum. Just let me know...