This　paper　discusses　non-ideal　issues　in　a　fully　passive　noise　shaping　successive　approximation　register　analog-to-digital　converter.　The　fully　passive　noise　shaping　techniques　are　realized　by　switches　and　capacitors　without　operational　amplifiers　to　be　scalable　and　power　efficient.　However,　some　non-ideal　issues,　such　as　parasitic　capacitance,　comparator　noise,　thermal　noise,　will　affect　the　performance　of　the　noise　shaping　and　then　degrade　the　final　achievable　resolution.　This　paper　analyzes　the　effects　of　the　main　non-ideal　issues　and　provides　the　design　reference　for　fully　passive　noise　shaping　techniques.　The　analysis　is　based　on　2nd　order　fully　passive　noise　shaping　SAR　ADC　with　an　8-bit　architecture　and　an　OSR　of　4.