| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an AM modulation signal detecting circuit comprising a reception preamplifier with superior minimum reception sensitivity characteristics by suppressing influences of noise caused by a bias circuit VB and improving an S/N of a receiving section. <P>SOLUTION: In an AM modulation signal receiving circuit of the present invention using a differential input type amplifier as a preamplifier (PA), an input bias of this preamplifier PA is supplied from a center tap provided in an antenna coil L. Thus, noise caused by the bias circuit becomes common-mode input noise of the differential input amplifier and does not appear in an output of the differential input preamplifier PA, thereby realizing the AM modulation signal receiving circuit which eliminates thermal noise or the like caused by the bias circuit. <P>COPYRIGHT: (C)2006,JPO&NCIPI |
