| 摘要 |
<p>PROBLEM TO BE SOLVED: To obtain a detection circuit simply constituted of a small number of parts by providing a bias circuit which gives a DC bias potential in accordance with a received signal from an antenna, a rectifier circuit which rectifies the received signal from the antenna at a bias point to extract a sub-carrier signal. SOLUTION: A fixed bias potential is given to the signal, which is received by the antenna, by the bias circuit, for example, a resistor bleeder circuit of resistors R2 (41) and R1 (42). That is, a minute bias current is always made to flow to the base of a transistor TR Tr1 (44) to secure the operation in the linear area of the TR 44 independently of the input signal level. This TR 44 operates as an input buffer and a rectifier diode. The output bias potential of a rectifier circuit comprises of the TR 44, a resistor R4 (45), and a capacitor C1 (46) is fixed by the charge potential of the capacitor 46.</p> |
