ADCs ... noise is it normal?

Have you hung an oscilloscope on the ostensibly stable voltage that your A/D coverter is sampling? And on your reference voltage input?

With the ground clip of the oscilloscope probe attached to the 0V net close to the poit where the A/D converter is connected to the 0V net (pin 3) ...

Note that the LSB on your A/D converter output is only 76.3uV. The 123 LSB range on your raw data is a 10mV peak-to--peak excursion - you will need to set the scope gain fairly high and use AC coupling if you want to see this kevek of noise on an oscilloscope,

Unless your circuit has been carefully constructed, it is very likely that your A/D converter is okay, and correctly representng the rather noisy signal that you are giving it.

no i do not have osciloscope in here but i did like thist

i used tl431 to get 3V and connected it to Vref and Vin.. what i get is .. noise.. FF80 FFB8 FFB8 FFB8 FF8A FFBE FFA6 FF80 FFB8

any idea ?

best regards david

You need to look at _everything_. Start with your Vref. How is this generated?. How does it's ground connect to the ground of the ADC?. How is it smoothed?. Then the same questions for the sample voltage. Then how are the digital lines routed relative the analog signals?. You are actually achieving about 10bit accuracy. The ADC you have, on a properly laid out board, is capable of doing vastly better than this.

Best Wishes

Your PCB layout and power supply are probably not designed properly. I remember my first-ever 14ADC design: an ADSP2101 on a board, a power and ground trace pair running from power supply to the DSP, the ADC and the input amplifier (working in the mV ranges) in exactly that order. I think I got about 8 bits of noise.....

Meindert

design.

do

samples :

bad one?

Have you hung an oscilloscope on the ostensibly stable voltage that your A/D coverter is sampling? And on your reference voltage input?

With the ground clip of the oscilloscope probe attached to the 0V net close to the poit where the A/D converter is connected to the 0V net (pin 3) ...

Note that the LSB on your A/D converter output is only 76.3uV. The 123 LSB range on your raw data is a 10mV peak-to--peak excursion - you will need to set the scope gain fairly high and use AC coupling if you want to see this kevek of noise on an oscilloscope,

Unless your circuit has been carefully constructed, it is very likely that your A/D converter is okay, and correctly representng the rather noisy signal that you are giving it.