一种用于金属安检门微弱信号处理电路的设计

Design of Analog Circuit for Weak Signal Processing Used in Metal Security Doors

针对金属安检门长期存在的误报、漏报问题,本设计采用了AD637真有效值转换、差动放大和窗口比较的微弱信号处理电路。改变峰值检测和模数转换的传统设计方式,利用差动放大器的对称性和两输入端时间常数不同达到抑制干扰的目的,通过带通滤波与窗口比较输出数字信号后,由单片机识别并报警。本设计可有效提高探测灵敏度,增强抗干扰能力,降低误报漏报率,并且降低成本。实测表明,本电路可探测30 cm范围内3 cm长铜丝。

In order to deal with the problems of false positives and false negatives for metal security doors, a weak signal processing circuit with AD637 true RMS（ root mean square） conversion, differential amplifier and window comparator is designed to instead of the traditional circuits with peak detection and digital-to-analog conversion. A differential amplifier is used to suppress interference signals with the difference time of capacitor charging and discharging. Through amplifying, bandpass-filtering and a window comparator, the signal is pro- cessed into a digital signal, which is received and alarmed by MCU（ microcontroUer unit）. Experiments show that the circuit has many features, such as high detection sensitivity, high anti-interference ability and low cost, and can reduce effectively the rate of false positives and false negatives. It can detect a 3 em long copper wire within 30 cm range.