DC is changed and I can't calibrate it
I could get signal in 15 bit resolution without noise but the changing DC is a
problem. Can you give me some advice?
The AD73360 was marketed for the voice band and power metering market. In these
applications, the dynamic AC specification, SNR ratio is the dominant factor
determining o/p resolution. The AD73360 is a 16 bit converter, in that the o/p
uses 16 bits, however the resolution will, depend on the SNR performance in the
o/p signal bandwidth.
Refer to the specification page 2 of the datasheet. The SNR from 0 to FS/2 for
FS =8Khz is typ 77dbs and decreases with the input signal level. In order to
get an increase in SNR, you will need to band limit your input filter stage
using a low pass first order filter(refer to page 25 of the datasheet) and
bandlimit the o/p in the DSP with a digital filter.
As you will notice from the datasheet, the DC specifications given are limited,
and do not include the effect of gain error and ADC non-linearity. This is
typical where converters are used in AC applications where operation down to DC
is not required.
In addition you will note, that the absolute value of the reference and drift
is not very good. To improve on the ref performance in terms of accuracy and
drift, you may overdrive it with an external source.