A circuit which converts the resistive signal directly into frequency signal is presented. Based on the impedance conversion circuit

the resistance of the sensor can be converted into equivalent inductance or capacitance

and the resonant circuit can be formed to realize the characterization of frequency offset signal to the sensitive signal of the resistive sensor. The parasitic effect under high frequency is analyzed and corrected by comparing the sensor simulation with the actual measurement. The sensitivity of frequency to the change of resistance is increased by adjusting the circuit parameters. Finally

commercial sensors are used to measure formaldehyde. The results show that the sensor can simply convert the resistance change into frequency signal

and should be applied to the Internet of things（IoT） for wireless sensing.