Electronic – Using ADC AD9057

adcanalognoisesignal processing

I use AD9057 with fpga in my oscilloscope project. Here is the ADC pin-out
pinout

I use the following scheme to test ADC:
VREF OUT connected to VREF IN, this gives internal reference voltage +2.5V

Vd +3.3 V

VDD +5 V

Encode – clock signal 3.3V (i have tried different frequencies according to datasheet)

I use constant voltage level from 2V (00000000) to 3V(11111111) according to datasheet (for Vref 2.5V), and i try to see valid bit patterns on D0-D7 pins, but it seems that only noise there.

1.) Is my test valid?

2.) I found a scheme in datasheet

ADC simple scheme from datasheet

And i don't understand why AIN is blocked with capacitor (how can i measure constant voltage in this case?) In my test i use the same scheme but without this capacitor. Maybe this is the reason of ADC's strange behavior?

Best Answer

In the same datasheet , indeed, on the same page is the following diagram: enter image description here

The diagram you've included above is captioned "capacitively coupled"

Given you're only capacitively coupling a DC signal you should only see "noise".