A corner detector comprises a PMOS threshold voltage detector and an NMOS threshold voltage detector, the PMOS threshold voltage detector is composed of a first clock terminal, a first CMOS inverter, a first capacitor, a PMOS threshold voltage function generator and a first voltage output terminal, wherein the PMOS threshold voltage function generator is electrically connected to the first capacitor and applied to generate a first formula of voltage signal as a function of threshold voltage, the NMOS threshold voltage detector is composed of a second clock terminal, a second CMOS inverter, a second capacitor, an NMOS threshold voltage function generator and a second voltage output terminal, wherein the NMOS threshold voltage function generator is electrically connected to the second capacitor and applied to generate a second formula of voltage signal as a function of threshold voltage.