| 摘要 |
PURPOSE:To prevent generation of noise and howling attended with changeover by controlling the timing of on/off of a transmission voice output and a hand- free talking circuit in changing over the hand-free talking mode and the other talking modes. CONSTITUTION:A delay circuit 21 retards 1 hand-free selection signal A by a time gamma to produce a signal A'. A OR circuit 22 and a AND circuit 23 generate respectively control signals B, C by using the signals A, A'. The signal B makes the hand-free circuit 7 operative. A transmission voice interruption circuit 24, in receiving the signal C, turns off a transmission voice output sent from the circuit 7 to the circuit 3 via a talking circuit 2. In this case, the timing of the signals A, A', B, C is as shown in a figure. Thus, when the mode is changed from the handset talking mode or the speaker reception mode into the hand-free talking mode or vice versa, sending of noises at change over or howling between a speaker 8 and a microphone 9 is prevented. |
