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Ahoana ny fiasan'ny telefaona finday?

FIAINANA: 2022-09-22 HITS: 74

Ahoana a telefona aoparilera miasa?


When there is no sending signal and receiving signal, the hands-free communication circuit should work in the receiving signal state. At this time, the attenuation of the transmit attenuator LS in the circuit is very large, while the attenuation of the receive attenuator LR is very small, so that the receive path is opened for amplification. In AS, the output of the sound-activated hands-free phone schematic diagram of the amplifier is divided into: one output signal is sent to the comparator B, and the other is sent to the transmission attenuator LS. In comparator B, the amplitude of the input signal is compared with the amplitude of the received signal. When comparing the strength of the transmitted signal, the comparator outputs a high (or low) level, thereby turning on the transmit attenuator. Disconnect the receive attenuator. In this way, the attenuation of the transmit attenuator is very small to ensure the smoothness of the transmit signal channel, so that the hands-free call circuit enters the call transmit state, and the transmit signal is sent to the transmit amplifier stage AS2 through the LS. After being amplified by AS2, the audio signal is sent to the outside line to contact the other party's telephone.

The voice current signal sent by the other party's telephone is sent to the receiving attenuator LR through the external line, and then sent to the receiving power receiving amplifier through LR for amplification, and the amplified signal is sent to the comparator B to compare with the sending signal. , the comparator will output a low (or high) level, so that the attenuation of the receiving attenuator LR that controls the receiving channel is greatly reduced, and the attenuation of the variable attenuator of the transmitting channel is increased. At this time, the hands-free voice-activated call circuit is in the receiving state.

During a hands-free call, the distance between the caller and the telephone is greatly increased. Due to the lengthening of the air channel, the problems of enhanced reverberation and reduced signal-to-noise ratio are brought about. According to the acoustic principle of the room, part of the user's speech sound is directly sent to the receiver, and the other part is sent to the microphone after being reflected by the environment. Since human hearing is delayed, the effect of directly reflected sound waves has little effect. Some of the reverberation sounds sent in random phases after multiple reflections from walls, desktops, floors, and ceilings may not be canceled, which affects the clarity of the call, resulting in the so-called hollow effect. The existence of reverberation, on the one hand, reduces the level difference between the direct sound of the sent speech and the reverberation sound caused by the reverberation in the room, and increases the sense of reverberation; on the other hand, it also reduces the level difference between indoor language and noise. , which reduces the signal-to-noise ratio of the signal.

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