Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
1997-07-03
2001-08-07
Hudspeth, David R. (Department: 2741)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S570000, C455S297000, C381S071400, C381S094700
Reexamination Certificate
active
06272360
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a remotely installed transmitter capable of clearly picking up the speaker's voice despite being installed away from the speaker's mouth and to a hands-free two-way voice terminal device using such a transmitter.
In recent years, the use of portable telephones has increased tremendously. Many people carry portable telephones with them and use them in their cars while driving. Usually, however, the portable telephone must be held to use, which is not desirable from the standpoint of careful driving.
Therefore, a device has been developed with which a person can talk using a portable telephone but without using his hands. In this device, a transmitter is installed approximately 30 to 60 cm in front of the driver, such as on the sun visor of the car, and a speaker is installed under the driver's seat or in a similar place.
When the two-way simultaneous speech is conducted using such a transmitter and a speaker, however, the voice level of the speaker becomes less than about one-third that of the ordinary handset-type telephone, which picks up the voice signal close to the mouth, since the transmitter is located at a considerable distance from the mouth of the speaker. Therefore, ambient noise is likely to be picked up, making hands-free communication difficult in a noisy environment. To carry out two-way speech, furthermore, the signal from the speaker must be heard at the same time. Thus, unless the acoustic coupling is decreased between the transmitter and the speaker, feedback and echo occur.
Therefore, the above-mentioned device has been furnished with a circuit which lowers he sensitivity of the transmitter circuit at the time of reception and lowers the sound volume of the receiver circuit at the time of transmission. This prevents the occurrence of feedback and echo during the two-way communication.
SUMMARY OF THE INVENTION
When the external noise at a level nearly equal to, or higher than the voice level of talk enters the transmitter as would happen when the car radio is producing a large sound volume, when the ambient noise is large due to high-speed running of the car, or when the ambient noise is increased as a result of opening a car window, however, the circuit employed in the above-mentioned conventional hands-free device erroneously judges the noise to be speech and erroneously lowers the sound volume of the receiver circuit, hindering voice communication to a serious degree.
In addition, in conventional hands-free devices, the sound volume of transmission and the sound volume of reception are changed over and adjusted by detecting an average value of transmission voice level or reception voice level. Such detection is accompanied, however, by a predetermined change-over delay causing speech to be interrupted during the change-over period.
The present invention has as one of its objects to solve the above-mentioned problems and to provide a remotely installed transmitter that is capable of clearly picking up only the voice of the speaker despite being installed away from the speaker's mouth and that does not cause feedback despite increased sensitivity, and to provide a hands-free type two-way voice terminal device using such a transmitter.
It is also desirable to provide remotely installed transmitter wherein a bidirectional microphone is installed at a central position in a pipe having a predetermined length. Sound pick-up ports are formed at suitable positions at least at the right and left ends of the pipe, and two sound pick-up chambers are formed in the pipe, one on the right side of the microphone and the other on the left side of the microphone. The two sound pick-up chambers are stuffed with a sound-absorbing material. The shapes and sizes of the sound pick-up chambers are determined so that minimum voice resonance frequencies of the two sound pick-up chambers when they stuffed with the sound-absorbing material are both higher than the used upper-limit frequency of voice of the transmitter. The amount of the sound-absorbing material is adjusted so that the voice frequency characteristics acquire monotonous attenuation characteristics in a voice frequency band higher than the used upper-limit frequency of voice.
Furthermore, it is desirable that the shapes and sizes of the two sound pick-up chambers are determined so that minimum voice resonance frequencies of the two sound pick-up chambers when they are not stuffed with the sound-absorbing material are both higher than the used upper-limit frequency of voice of the transmitter. The amount of the sound-absorbing material is adjusted so that the sensitivities at minimum voice resonance frequencies of the sound pick-up chambers after being stuffed with the sound-absorbing material are not higher than twice the sensitivity at 1 KHz. Furthermore, the frequency response of the transmitter starts showing a monotonously attenuating response at the high frequency response range, and is higher than two-thirds of the used upper limit frequency of the voice frequency band of the transmitter. The length from the tip of the pipe to the central position of the microphone is selected to be not longer than ¼ of the wavelength of the used upper-limit frequency of voice of the transmitter.
It is further desired to connect an ambient noise suppressing circuit to the output terminal of the bidirectional microphone, the ambient noise suppressing circuit having such amplification characteristics that the amplification gain thereof increases with an increase in the output level of the microphone. The ambient noise suppressing circuit comprises a gain controller for amplifying an output signal of the microphone, a band amplifier for passing signals of a particular frequency band only among the signals output from the bidirectional microphone, a peak detector for detecting a peak value of the signals that have passed through the band-pass amplifier, and a holding circuit for holding the peak value output by the peak detector for a predetermined period of time to control the amplification gain of the gain controller depending upon the peak value.
The two-way voice terminal device of the present invention is preferably equipped with a transmitter and a receiver that can be used hands-free, the transmitter being remotely installed, wherein the receiver is mounted on a first fixing portion being directed to the ear of the speaker, and the transmitter being mounted on a second fixing portion remote by a predetermined distance from the mouth of the speaker in a manner that a tip of the pipe is directed toward the speaker.
Furthermore, it is desirable that the receiver and the transmitter are arranged within a vehicle. The receiver may be mounted on a center pillar and the transmitter may be mounted on a sun visor. Or, the receiver may be mounted on a side surface of a headrest of a seat and the transmitter may be mounted on the other side surface of the headrest. Or, the receiver and the transmitter may be mounted on a belt member detachably attached to the headrest of the seat, the receiver and the transmitter being located on the right and left sides of the headrest to be separated away from each other.
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Konomi Masao
Yamaguchi Noboru
Finnegan Henderson Farabow Garrett & Dunner LLP
Hudspeth David R.
Lerner Martin
Pan Communications, Inc.
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