| 摘要 |
PURPOSE:To surely detect a reception signal by absorbing an echo to detour from a transmission part to a reception part with a calling signal filter and a response signal filter and sending a delayed signal having no transient response to the reception part by a delay means switched by a switching means when the phase of a transmit signal is changed. CONSTITUTION:Under a calling response mode, a calling response signal is sent from a transmission part 11, the echo to detour from the transmission part 11 to a reception part 12 is generated, and the echo is absorbed with calling response signal filters 16 and 17. Further, when the phase of the calling response signal is changed, the transient response is generated in the outputs of the calling response filters 16 and 17, and since the filter outputs are switched to the output of a delay means 21 by a switching means 23 for prescribed time synchronously with the change of the phase, the outputs from the calling response signal filters 16 and 17 are delayed by the delay circuit 21 for an integral multiple of a cycle. Consequently, the delayed signal having no transient response is sent from the delay circuit 21 to the reception part 12. Thus, a situation in which the reception signal is erroneously detected or cannot be detected due to the transient response can be prevented. |
