This invention provides a system in package integrated circuit with self-generating reference voltage, in which includes a logic circuit chip and a memory chip. The logic circuit chip generates a plurality of output signals, and the memory chip includes a plurality of input circuit receiving the plurality of output signals from the logic circuit chip. The memory chip further includes a voltage generator generating an input reference voltage based on an output supply voltage. The memory chip is compatible with DDR standard and the plurality of input circuit thereof is compatible with SSTL_2 standard. Wherein, each input circuit comprises a comparator with a first input terminal receiving one of the plurality of output signals and a second input terminal receiving the input reference voltage.