The invention discloses a passive
noise shaping successive approximation SAR analog-to-
digital converter. The analog-to-
digital converter comprises three capacitive digital-to-analog
converters (CDACs), a passive
loop filter, a
comparator and an SAR logic circuit, wherein the three identical CDACs comprise a CDAC1 required by normal SAR conversion and two auxiliary CDAC2 and CDAC3 used for generating a margin
voltage of a previous period. Two interlaced CDAC2 and CDAC3 are added, and KT / C
noise and
gain loss introduced by passive margin sampling are removed. Wherein the CDAC1 generates the margin
voltage Vres (n) of the
current period, and the CDAC2 and the CDAC3 alternately generate the margin
voltage Vres (n-1) of the previous period. And the passive
loop filter carries out
noise shapingon the margin voltage and suppresses in-band noise of the
signal. And the
comparator quantizes the analog output of the passive
loop filter into a digital code, the digital code toggles the next
capacitor switch in the CDAC through the SAR logic circuit until the conversion is finished, and all the digital codes are sequentially spliced together to serve as the output code of the SAR ADC, which is the same as that of the common SAR ADC. According to the invention, the second-order
noise shaping effect can be realized, the
signal in-band quantization noise and the
comparator noise are effectively suppressed, and the
signal-to-noise ratio and the spurious-free
dynamic range of the SAR ADC are obviously improved.