Abstract: In a radar sensor, a transmitting antenna is configured to radiate a transmitted RF signal, a receiving antenna is configured to receive a reflected RF signal from a target, and a frontend circuit is configured to calculate the distance between the target and the radar sensor by measuring the frequency shift between the transmitted RF signal and the reflected RF signal. The frontend circuit includes a crystal-less signal synthesizer configured to generate the transmitted RF signal without using a crystal, and a mixer configured to provide an IF-band signal associated with the frequency shift between the transmitted RF signal and the reflected RF signal by mixing the reflected RF signal and the transmitted RF signal.