I am a freshman for ADC design.
when i use a SAR ADC with sample clock about 2.4 MHz for input signal, whose bandwidth is 100 KHz. We have OSR=12. When finished adc conversion, do we need a digital filter after ADC ?
The quantization noise is spread about(0, 1.2MHz) while signal bandwith is only about 100KHz. If we use a digital filter, we can suppress the noise from 100K to 1.2MHz and SNDR will increase a little bit. Is it correct ?

ZRSH001,

 Unless you are doing something special with the SAR ADC you do not
need a digital filter. For a SAR ADC with oversampling, you need to
average the outputs. Store the value of out[n] in a register and add it
to the output of the current conversion.
              out[n]=out[n-1]+ADCOUT

When you get done keep the top X number of bits that you need,
where X is the number of bits of the ADC.

  Unlike an oversampling ADC, oversampling of a Nyquist-Rate ADC
provides limited improvements in the dynamic range. For example,
a 2x oversample rate provides a 3dB improvement, a 4x oversample
rate provides a 6dB improvement.

  Note: this behavior is different than the behavior of a Delta-Sigma
           ADC.

                                                                   Best Regards,

                                                                       Sheldon