A method and a circuit for am demodulation

摘要

The invention relates to a method for simultaneous AM demodulation of data which are transferred between a transponder and an interrogator in connection with metal detection. The carrier wave signal is amplitude modulated by the information signal and is fed to an input of a receiver where it is branched into two parts, so that the first part is fed to a severe limiter, while the second part is fed to a first input of a mixer whose second input receives the output signal from the severe limiter. The two signal parts are multiplied in the mixer. A DC signal used for metal detection and an AC signal used for determining a possible information signal occur on the output of the mixer. The AM signal is fed to the receiver from an antenna which contains an adjusted circuit, which receives a signal galvanically separated from a generator. Signals from objects which partly contain a tag with identification data and partly do not contain a tag, may be used for detection and identification of objects.