| 摘要 |
Hands-free control circuitry for a mobile radiotelephone is described that allows hands-free voice communications in a vehicular environment having a high level of ambient background noise. The hands-free control circuitry includes switches in the audio path from a microphone to the radio transmitter and the audio path from the radio receiver to a speaker, where, at all times, one audio path is closed to pass audio signal and the other audio path is open to block audio signals. The presence or absence of audio signals from the mobile party via the microphone and land party via the radio receiver is determined by separate detecting circuitry including a logarithmic amplifier, envelope detector, valley detector and summing circuitry, and comparator. Whenever the envelope of the audio signals exceeds its minima by an amount greater than a reference voltage, the detecting circuitry generates an output signal indicating that audio signals have been detected. Control logic is coupled to the output signals from the land party and the mobile party detecting circuitry for closing and opening the switches in the audio paths. One party may break-in on the other by closing his audio path and opening the other's audio path. The audio path of a speaking party is closed if the output signal from his detecting circuitry indicates that audio signals have been detected and the output signal from the other party's detecting circuitry has been absent for a predetermined time interval. The inventive hands-free control circuitry provides for fast break-in by either party, while minimizing spurious path switching. Furthermore, the hands-free control circuitry may also be utilized in landline telephone applications. |
