An A/D converter apparatus for converting an analog signal output from an anti-aliasing
filter into a digital signal, a sinc filter for removing a frequency component
corresponding to an aliasing noise generated by down-sampling, a first decimator
for down-sampling a signal output from the sinc filter, a low pass filter for removing
a frequency component corresponding to an aliasing noise generated by down-sampling,
a second decimator for down-sampling a signal output from the low pass filter,
and a high pass filter for removing a dc component from a signal output from the
second decimator are disclosed.