| 摘要 |
PURPOSE:To decrease the number of external connection terminals by providing a switching transistor which is controlled via an external connection terminal and selecting a transmission line for input signal. CONSTITUTION:A transistor TRQ11 is turned off when a switch SW1 is off. Then a sound signal fR is supplied from an input terminal T11. Therefore TRs Q17 and Q18 are turned on alternately to cause the voltage drops alternately to load resistances R21 and R22. These voltage drops are supplied to an amplifying circuit 23. In this case, an FM wave detecting circuit 21 is kept inactive together with the TRQ11 turned off. Therefore the sound signal does not appear at all. The TRs Q11 and Q12 are turned on when the SW1 is on, and at the same time the TRs Q14 and Q15 are turned on. As a result, no base current flows to the TRs Q16 and Q21 and are turned off. Then a TRQ22 is turned on to actuate a circuit 21. |
