Abstract: An improved infrared ray sensor driving circuit capable of advantageously controlling an amplifying level and a cut-off frequency of a filter by separating the functions of an amplifier and a filter, respectively. The circuit includes an impedance matching circuit for converting a high impedance of the signals detected to a low impedance signal, a first amplifying circuit for amplifying signals outputted from the impedance matching circuit by a first predetermined gain, a filtering circuit for filtering the signals outputted from the first amplifying circuit to pass frequencies of a predetermined bandwidth, and a second amplifying circuit for amplifying the signals outputted from the filtering circuit by a second predetermined gain.

Abstract: A human body sensing device capable of sensing not only the presence of the human body, but, also the human body's position. The device includes a lens unit, for dividing a room to be monitored into a plurality of lateral and vertical zones and projecting an infrared ray emitted from an object present in one of the zones, a filter unit, for filtering only an infrared ray emitted from the human body from infrared rays received from the lens unit, and an infrared sensor unit for sensing the human body's position, based on the infrared ray received from the filter unit.