| 摘要 |
PURPOSE:To decrease the number of component parts and to attain the cost reduction in an RF.AGC circuit of a 1-system diversity tuner, by connecting a resistance to an antenna switch circuit to attenuate the high frequency gain in a conduction mode and energizing said resistance in a strong field mode. CONSTITUTION:The output of an RF.AGC terminal of a front end circuit 4 is set at an H level in a medium or weak field mode. While transistors TRQ1 and Q2 are kept ON and a resistance R3 is not energized. Thus the value of the current flowing through PIN diodes D1 and D2 is decided by resistances R1 and R2 only. In a strong field mode the output of the RF.AGC terminal of the circuit 4 is set an L level. Then the TRQ1 and Q2 are turned off and the R3 is energized. Thus the value of the current flowing through the diodes D1 and D2 is affected by the resistance R3. Then the high frequency gain of an antenna switch circuit is attenuated. |
