Systems and methods for object detection are provided. The system includes at least a coil, a small signal generator, a small signal receiver, and a processor. The small signal generator includes a digital-to-analog converter circuit with programmable impedance. The small signal generator is configured to select an output impedance for the digital-to-analog circuit for capacitive sensing or radio-frequency identification (RFID) tag detection; generate a small signal according to the output impedance; and provide the small signal to the coil. The small signal receiver receives the small signal and a response signal associated with the small signal and measures the response signal to generate a measured signal. The processor compares the measured signal with one or more reference signals and performs capacitive sensing and/or detect a RFID tag according to the comparison.