I am totally frustrated with the behavior of my signal processing board based on AD9269 16 bit 20MSPS ADC. I use FPGA to write a couple of bytes at the startup of the system to configure the ADC. In most cases it works but sometimes (say 10% of attempts) it doesn't. What is really strange that it depends on the signal applied to the analog inputs. With zero signal the failure is seldom but simply touching the input with the finger leads to the configuration error. The same effect is with applying any external signal to the input.
We have tried reading the signals back from the registers and in case of failure some bits are wrong there. Checking signals with a scope shows that everything is OK at the pins of ADC, no overshots and no ripple at all. Analog supply is 1.8V, I/O supply is 3.3V. Differential conversion clock is applied continuously.
ADC is soldered to 4-layer PCB with separate grounds connected next to this ADC. First idea was bad contact of ground pad but I have double-checked it. The problem persists on two same boards and appears occasionally on other boards of the same type.
Do you have any ideas what could I try to solve this issue?