A signal modulator includes: a modulating circuit; a first signal trace block arranged to conduct a first in-phase oscillating signal to the modulating circuit, and conduct a first quadrature-phase oscillating signal to the modulating circuit; and a second signal trace block arranged to conduct a second in-phase oscillating signal to the modulating circuit, and conduct a second quadrature-phase oscillating signal to the modulating circuit, and a phase difference of the first in-phase oscillating signal caused by the first signal trace block substantially equals a phase difference of the second quadrature-phase oscillating signal caused by the second signal trace block, a second quadrature-phase oscillating signal to the modulating circuit, and a phase difference of the second in-phase oscillating signal caused by the second signal trace block substantially equals a phase difference of the first quadrature-phase oscillating signal caused by the first signal trace block.