A signal demodulation device includes an IQ mixer, a differential element and a signal processor. The IQ mixer is configured to output a first mixed signal and a second mixed signal. The differential element is electrically connected to the IQ mixer for receiving the first and second mixed signals and configured to differentiate the first and second mixed signals and output a first derivative signal and a second derivative signal. The signal processor is electrically connected to the differential element for receiving the first and second derivative signals and configured to demodulate the first and second derivative signals and output a first demodulated signal.