Transmission system for still-picture TV telephone

• US 5,063,587 A
• Filed: 03/29/1990
• Issued: 11/05/1991
• Est. Priority Date: 03/30/1989
• Status: Expired due to Fees

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Ueno, Yutaka, Semasa, Takayoshi
• Primary Examiner(s): Dwyer, James L.
• Assistant Examiner(s): Chan, Wing F.
• Application Number:
  US07/500,890
• Time in Patent Office: 586 Days
• Field of Search: 379/53, 379/54, 379/93, 379/96-98, 358/85
• US Class Current: 348/14.14
• CPC Class Codes: H04M 11/062 using different frequency bands for speech and other data
• CPC Class Codes: H04N 7/12 Systems in which the television signal is transmitted via one channel or a plurality of parallel channels, the bandwidth of each channel being less than the bandwidth of the television signal H04N7/24 takes precedence
• CPC Class Codes: H04N 7/147 Communication arrangements, e.g. identifying the communication as a video-communication, intermediate storage of the signals selecting H04Q
• CPC Class Codes: H04N 7/148 Interfacing a video terminal to a particular transmission medium, e.g. ISDN

Abstract

A still-picture TV telephone system for transmitting and receiving, via a telephone circuit, a still picture taken by a camera; a picture signal stored in a memory is modulated in phase and amplitude digitally and is offered or supplied to the telephone circuit during talking in voice. To superposing the talk in voice also during offering of the picture signal, the voice and picture signals are divided by frequency band. The frequency band of the voice signal is partially restricted, and the picture signal is inserted in the omitted band, during which time the picture signal is restricted in band by setting the band rate frequency to be lower than the carrier signal frequency when modulating the phase and amplitude. The picture signal is further restricted in band by a low-pass filter so that the voice and picture signals are separated by band so as not to overlap each other at the same frequency band.

Claims

1. A still-picture TV telephone system for transmitting and receiving, via a telephone circuit, a still picture taken by a camera, comprising:

(a) a voice band filter means for eliminating a special band signal of a voice signal introduced from a transmitting means;

(b) a low-pass filter means for restricting a still picture signal in band, cut-off frequencies of said low-pass filter means being set to less than or equal to 1/2 of the restricted band of said voice band filter means;

(c) a phase/amplitude modulation means for modulating the phase and amplitude of the still picture signal, high frequency components of which have been eliminated, by a carrier signal, frequencies of the carrier signal being set to substantially central frequencies of the signal-free band of said voice band filter means, a baud rate frequency being set substantially to the restricted band width of said voice band filter means; and

(d) a composer means for composing a picture transmission signal of modulated phase and amplitude in the narrow band and a voice transmission signal of the restricted band to divide frequency bands of the picture and voice signals and, at the same time, to transmit the picture and voice signals.

2. A still-picture TV telephone system according to claim 1, wherein the baud rate frequencies of said phase/amplitude modulation means is set to 1/n of the carrier signal frequencies, where n stands for an integer.

3. A still-picture TV telephone system according to claim 2, wherein the baud frequencies of said phase/amplitude modulation means is set to 1/3 of the carrier signal frequency.

4. A still-picture TV telephone system according to claim 1, wherein said low-pass filter means is a filter having a roll-off characteristic.

5. A still-picture TV telephone system according to claim 1, wherein said voice band filter means has a filter characteristic so as to leave both low and high frequency ranges of the voice signal.

6. A still-picture TV telephone system for transmitting and receiving, via a telephone circuit, a still picture taken by a camera, comprising:

(a) a voice band filter means for eliminating a special band signal of a voice signal introduced from a transmitting means;

(b) a low-pass filter means for restricting a still picture signal in band, cut-off frequencies of said low-pass filter means being set to less than or equal to 1/2 of the restricted band of said voice band filter means;

(c) a phase/amplitude modulation means for modulating the phase and amplitude of the still picture signal, high frequency components of which have been eliminated, by a carrier signal, frequencies of the carrier signal being set to substantially central frequencies of the signal-free band of said voice band filter means, a baud rate frequency being set substantially to the restricted band width of said voice band filter means; and

(d) a composer means for composing a picture transmission signal of modulated phase and amplitude in the narrow band and a voice transmission signal of the restricted band to divide frequency bands of the picture and voice signals and, at the same time, to transmit the picture and voice signals; and

(e) a receiver circuit for receiving a transmitted voice-and-picture composite signal and for separating the composite signal in band.

7. A still-picture TV telephone system according to claim 6, wherein said receiver circuit includes a voice separating band-pass filter having a filter characteristic similar to that of said voice band filter means.

8. A still-picture TV telephone system according to claim 6, wherein said receiver circuit includes a demodulator circuit composed of a multiplier circuit for mixing the received signal and the carrier signal, and a low-pass filter for eliminating the high frequency components of output of said multiplier circuit, said low-pass filter having a filter characteristic similar to that of said low-pass filter means.

9. A still-picture TV telephone system according to claim 8, further comprising a carrier reproduction circuit for separating the carrier signal from the received signal to obtain a carrier signal to be mixed in said demodulator circuit.

10. A still-picture TV telephone system for transmitting and receiving, via a telephone circuit, a still picture taken by a camera, comprising:

(a) a voice band filter means for eliminating a special band signal of a voice signal introduced from a transmitting means;

(b) a pair of low-pass filter means for restricting a still picture signal in band, cut-off frequencies of said low-pass filter means being set to less than or equal to 1/2 of the restricted band of said voice band filter means;

(c) an I phase/amplitude modulation means for modulating the phase and amplitude of the still picture signal, outputted from one of said pair of low-pass filter means, by a carrier signal of 0 degree phase, frequencies of the carrier signal being set to substantially central frequencies of the signal-free band of said voice band filter means, baud rate frequencies being set substantially to the restricted band width of said voice band filter means;

(d) a Q phase/amplitude modulation means for modulating the phase and amplitude of the still picture signal, outputted from the other low-pass filter means, by a carrier signal of 90 degree phase, frequencies of the carrier signal being set to substantially central frequencies of the signal-free band of said voice band filter means, a baud rate frequency being set substantially to the restricted band width of said voice band filter means; and

(e) an amplitude composer circuit for composing the modulated outputs of both said I and Q phase/amplitude modulation means; and

(f) a composer means for composing a picture transmission signal of modulated phase and amplitude in the narrow band and a voice transmission signal of the restricted band to divide frequency bands of the picture and voice signals and, at the same time, to transmit the picture and voice signals.

11. A still-picture TV telephone system according to claim 10, wherein the baud rate frequency of said phase/amplitude modulation means is set to 1/n of the carrier signal frequencies, where n stands for an integer.

12. A still-picture TV telephone system according to claim 11, wherein the baud rate frequency of said phase/amplitude modulation means is set to 1/3 of the carrier signal frequencies.

13. A still-picture TV telephone system according to claim 10, wherein said low-pass filter means is a filter having a-roll-off characteristic.

14. A still-picture TV telephone system according to claim 10, wherein said voice band filter means has a filter characteristic so as to leave both low and high frequency ranges of the voice signal.