| 摘要 |
PURPOSE:To improve the selectivity characteristic of a high frequency stage by providing an LC series resonance circuit which resonates almost at an image frequency outside of a reception band to the low-impedance signal line of the high frequency stage. CONSTITUTION:A trap circuit 1 is connected between the ground and connection point between an antenna input terminal IN and an input capacitor C1. This consists of the serial resonance circuit of an inductance coil L and a fixed capacitor C and constants of respective elements are set so that the circuit resonates almost at the image frequency outside of the reception band. Thus, the selectivity characteristics at the upper side of a reception frequency are improved, which is remarkable, specially at a high reception frequency. |
