Mobile telephone set with automatic level control means of sound signal

Abstract: In a portable telephone set having an audio-frequency amplifier (12) for amplifying a sound signal from a microphone (11) and a codec (13) for digitizing and coding the sound signal into a digital sound signal which is transmitted therefrom, a level of said sound signal is monitored (17) to produce a detected level and is averaged at a timing (18) and compared with level data stored in a memory (15), and an amplification control signal is produced. At least one of the audio-amplifier (12) and said codec (13) is controlled its amplification degree in response to the amplification control signal.

Description: Background of the Invention: The present invention relates to a mobile or portable telephone set and, in particular, to level control of a sound signal in such a portable telephone set. In the known portable telephone set or a mobile telephone set such as terminals in the Cellular Communication system, the Personal Handy-phone System and other wireless communication system, a sound signal inputted by a microphone is amplified by an audio-frequency amplifier. The amplified sound signal is digitized and coded by a codec into a digital sound signal which is carried on a carrier frequency signal and is transmitted as a wireless signal. The sound signal has different sound levels dependent on sound pressure of the utterance to the microphone. In the known portable telephone set, the sound level of the sound signal is not adjusted before transmitting therefrom. At receiving party, the sound level is only adjusted by a volume of sound. However, when the sound pressure of the utterance is excessively high, distortion is caused at the audio-amplifier and/or an overflow is caused at an analog/digital converter in the codec. As a result, sound is distorted at the receiver side. On the contrary, when the sound pressure is weak, the volume adjustment must be performed at the receiver side. Summary of the Invention: Therefore, it is an object of the present invention to provide a portable telephone set which can automatically control the level of the sound signal to transmit a sound signal with a constant level without relation to sound pressure of utterance to the microphone. According to the present invention, there is provided a portable telephone set comprising an audio-frequency amplifier for amplifying a sound signal from a microphone, a codec for digitizing and coding the sound signal into a digital sound signal, a digital signal processor for monitoring a level of the sound signal to produce a detected level, a memory for storing level data, and sound level controlling means for collating the level data stored in the memory with the detected level to control amplification degree of at least one of the audio-amplifier and the codec. The sound level controlling means preferably comprises: timer means for producing a timing signal at a predetermined time interval; a processor unit for storing the detected level into the memory, the processor unit responsive to the timing signal averaging the detected level stored in the memory to produce an averaged level and comparing the averaged level with the level data to produce an error level, the processor unit producing an amplification control signal corresponding to the error level; gain control means responsive to the amplification control signal for controlling the amplification degree of at least one of the audio-amplifier and the codec. The codec usually comprises a prefilter for passing the sound signal from the audio-frequency amplifier, an analog/digital converter for digitizing the sound signal into the digital signal, a digital gain controller for performing a gain control of the digital sound signal, and a bandpass filter for passing the digital sound signal. The prefilter is controlled by the gain controller to perform controlling the amplification degree of the codec. Alternatively, the digital gain controller is controlled by the gain controller to perform controlling the amplification degree of the codec . Brief Description of the Drawings: Fig. 1 is a block diagram of a known portable telephone set; Fig. 2 is a block diagram of a portable telephone set according to an embodiment of the present invention; Fig. 3 is a block diagram of a codec which is controlled by a gain controller; and Fig. 4 is another block diagram of the codec which is controlled by the gain controller in another fashion. Description of Preferred Embodiments: Prior to description of preferred embodiments of this invention, a known portable or mobile telephone set in the prior art will be described in connection with processing an audio or sound signal outgoing therefrom, with reference to Fig. 1. Referring to Fig. 1, the known portable telephone set 10 includes a microphone (MIC) 11 for converting speech into a sound or audio signal of an analog signal, a low-frequency amplifier (AMP) 12 for amplifying the sound signal to produce an amplified sound signal, a codec section (CODEC) 13 for digitizing and coding the amplified sound signal from the amplifier 12 to produce a digital sound signal which is carried on a wireless carrier frequency signal and is transmitted therefrom. On the other hand, a digital signal processor (DSP) 17 processes the sound signal coded at the codec 13 under control of a central processing unit (CPU) 19. In the known portable telephone set, an amplification degree of the amplifier 12 and an amplification degree of the codec 13 are set to fixed values, respectively, during communication. Therefore, the sound signal has a sound level which is corresponding to a sound pressure uttered towards the microphone 11. Accordingly, an adjustment of the sound level has been performed by adjusting a volume to an adequate level at the other telephone set of the receiving party. Now, embodiments of the present invention will be described with reference to the drawings. Referring to Fig. 2, a portable telephone set 1 according to an embodiment shown therein also includes a microphone (MIC) 11 for converting speech into a sound or audio signal of an analog signal, a low-frequency amplifier (AMP) 12 for amplifying the sound signal to produce an amplified sound signal, a codec section (CODEC) 13 for digitizing and coding the amplified sound signal from the amplifier 12 to produce a digital sound signal which is carried on a wireless carrier frequency signal and is transmitted therefrom, a digital signal processor (DSP) 17 for monitoring codec 13 to notify, as a detected level, and a memory (MEMO) 15 for storing level data for controlling the level of the sound signal to be transmitted, like the known portable telephone set. The portable telephone set 1 further comprises a level controller for collating the level data stored in the memory 15 with the detected level to control amplification degree of at least one of the audio-amplifier 12 and the codec 13. The level controller comprises a central processing unit (CPU) 16 receives the detected level from the DSP 17 and stores the detected level into the memory 15. The central processing unit 16 averages the detected level signal stored in the memory 15 in response to a timing signal to produce an averaged level. Then, the central processing unit 16 compares the averaged level and the level data stored in the memory 15 to produce an error signal, and produce an amplification control signal. The portable telephone set 1 further comprises a timer(TIME) 18 for producing the timing signal to deliver the timing signal to the central processing unit 16, and a gain controller (GNC) 14 for controlling the amplification degrees of the amplifier 12 and the codec 13 in response to the amplification control signal. In operation, the sound signal inputted from the microphone 11 is amplified at the amplifier 12 and inputted into the codec 13. The amplified signal from the amplifier 12 is digitized and coded into a digital sound signal at the codec 13. The digital signal processor 17 monitors the digital sound signal to detect a sound level of the sound signal. The detected level is notified the central processing unit 16. The central processing unit 16 stores the detected level from the digital signal processor 17 into the memory 15, averages them at a given timing by the timing signal from the timer 18 to produce an averaged level. The central processing unit 16 further compares the averaged level with the level data preset in the memory 15 and instructs the gain controller 14 by the gain control signal to change the amplification degree of the amplifier 12 and the codec 13. Thus, the amplification degree of the amplifier 12 and the codec 13a are controlled to thereby change the level of the sound signal transmitted to an adequate sound level. The timer 18 is preset a time interval to produce the timing signal, and the time interval preset is also stored in the memory 15. Referring to Fig. 3, the codec 13 comprises a prefilter (PRF) of a gain controllable type 131 for passing the sound signal from the amplifier 12, an analog/digital converter (A/D) 132 for digitizing the sound signal to a digital sound signal, a digital gain controller (DGC) 133 for performing a gain control of the digital sound signal, and a bandpass filter (BPF) 134 for passing the digital sound signal. When controlling the amplification degree of the codec 13 according to the instruction by the amplification control signal from the central processing unit 16, the gain controller 14 performs the control for the prefilter 131. That is, gain controller 14 controls the gain of the prefilter 131 or the attenuation level over the frequency pass band of the prefilter 131. Alternatively, the gain controller 14 performs the control for the digital gain controller 133, as shown in Fig. 4. That is, the control gain in the digital gain controller 133 is changed by the gain controller 14. In the embodiment described above, the gain controller 14 controls the amplification degree of the amplifier 12 or the codec 13 individually. However, it can be easily done to control both the amplifier 12 and the codec 13 in a combined fashion.

Claims: A portable telephone set comprising an audio-frequency amplifier (12) for amplifying a sound signal from a microphone (11), a codec (13) for digitizing and coding said sound signal into a digital sound signal, a digital signal processor (17) for monitoring a level of said sound signal to produce a detected level, and a memory (15) for storing level data, characterized by provision of sound level controlling means (14, 16, 18) for collating said level data stored in said memory with said detected level to control amplification degree of at least one of said audio-amplifier (12) and said codec (13). A portable telephone set as claimed in claim 1, wherein said sound level controlling means comprises: timer means (18) for producing a timing signal at a predetermined time interval; a processor unit (16) for storing said detected level into said memory (15), said processor unit (16) responsive to said timing signal averaging said detected level stored in said memory (15) to produce an averaged level and comparing said averaged level with said level data to produce an error level, said processor unit (16) producing an amplification control signal corresponding to said error level; gain control means (14) responsive to said amplification control signal for controlling said amplification degree of at least one of said audio-amplifier (12) and said codec (13). A portable telephone set as claimed in claim 2, wherein said codec (13) comprises a prefilter (131) for passing said sound signal from said audio-frequency amplifier (12), an analog/digital converter (132) for digitizing said sound signal into said digital signal, a digital gain controller (133) for performing a gain control of said digital sound signal, and a bandpass filter (134) for passing said digital sound signal. A portable telephone set as claimed in claim 3, wherein said prefilter (131) is controlled by said gain controller (14) to perform controlling the amplification degree of said codec (13). A portable telephone set as claimed in claim 3, wherein said digital gain controller (133) is controlled by said gain controller (14) to perform controlling the amplification degree of said codec (13).

Inventors: SATOH KAZUHISA, SATOH, KAZUHISA, Satoh, Kazuhisa, c/o NEC Saitama, Ltd.
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1997
Main classification: H03G3
IPC codes: H03G3, H04B1, H04M1, H04B7