| 摘要 |
<p>PROBLEM TO BE SOLVED: To surely prevent erroneous detection in spite of a change in a received signal level due to fluctuation by various disturbances by carrying out detection of existence/absence of an invader on the basis of a detection receiving level in a time after a lapse of one cycle of a Doppler shift output. SOLUTION: In response to a level change in both of an inverted pulse signal by an inverter 21 and a shaping signal from a waveform shaping circuit 60a, an EXOR gate 60b finds respective phase differences of the inverted pulse and the shaping signal so as to generate a phase difference pulse signal. In an amplification circuit 70, a constituent corresponding to invasion of a person is extracted from a signal constituent of the phase difference pulse signal so as to be amplified by using a reference voltage Vref in a reference signal generation circuit 40 as a reference for generating a Doppler shift signal, which is shaped into a Doppler shaped pulse signal in a waveform shaping circuit 80. In this process, if an envelope detection signal from an envelope detection circuit 90 is a predetermined level Vth (equivalent to a lower limit level representing invasion of a person into a vehicle interior) or more, it is determined whether a Doppler shaped pulse signal exists in the waveform shaping circuit 80 or not, and the determined result is outputted to a microcomputer 100.</p> |
