i experience noise when i sample through 24 bit ad converter of micro. Data seem at first correct but when you measure the signal/noise i get not a good value.
I usally (with other hardware and micro) get 125dB with imputs shorted, sampling about 1Khz, but with MSP430 i get 95dB.
The conditioning circuit is the opamp ADA4841-2 (used other times).
To setup acquisition i do:
void AD_setup(void)
{
SD24CCTL0=SD24CCTL0|SD24GRP|SD24DF|SD24LSBTOG; //CH0 Interrupt enable, raggruppato con prox CH
SD24CCTL1=SD24CCTL1|SD24GRP|SD24DF|SD24LSBTOG; //CH1 Interrupt enable, raggruppato con prox CH
SD24CCTL2=SD24CCTL2|SD24IE|SD24DF|SD24LSBTOG; //CH2 Interrupt enable, CH master
SD24INCTL0|=SD24INCH_1; //CH0 select
SD24INCTL1|=SD24INCH_1; //CH1 select
SD24INCTL2|=SD24INCH_1; //CH2 select
SD24CCTL2=SD24CCTL2|SD24SC; //Start
_enable_interrupts();
}
Interrupt routine:
SD24CCTL2&=~SD24IFG; //reset flag
a=SD24MEM0;
a=a<<8;
b=SD24MEM0;
b=b>>8;
data=a+b;
before has been set the sampling frequency in this way (976.5Hz):
SD24CTL|=SD24DIV_2|SD24XDIV_1; //SMCLK/12
SD24CCTL0|=SD24OSR_1024;
SD24CCTL1|=SD24OSR_1024;
SD24CCTL2|=SD24OSR_1024;
I have tested even with MSP-ts430pw24 board simply shorting 2 ch zero pins with same results.
Enzo Ternavasio