| 摘要 |
PROBLEM TO BE SOLVED: To facilitate a countermeasure to a case that it is necessary to give either S/N or detecting sensitivity priority. SOLUTION: The lower limit of the reference voltage (Vr) of a comparator 10 for detection can be adjusted from the outside part by a variable type voltage lower limit limiter circuit 12 which is adjusted by a control voltage (VCL). In this case, such an adjustment is performed that the lower the reference voltage (Vr) of the comparator 10 for detection is, the higher the detecting sensitivity is, and the higher the reference voltage (Vr) of the comparator 10 for detection is, the lower the detecting sensitivity is. This detecting sensitivity has a large influence on a reception distance and noise-resistance. Thus, the reference voltage (Vr) is changed by the adjustment of the control voltage (VCL) so that either the detecting sensitivity or the noise-resistance can be given priority. |
