Design of detecting metal signal weak change detection circuit

In this paper, AD637 Root Mean Square (RMS) chip is used to convert the induced voltage signal in the coil into DC signals. A differential amplifier is used to convert the fast DC signal into a pulse signal with the difference time of capacitor charging and discharging. Then amplifying again and a window comparator was used to process the signal into a digital signal. Thus the data acquisition task of security doors is completed. The whole design had many features, such as high anti-jamming ability, high sensitivity, and so on. It can detect a dime size of the metal for 40 cm range.