JPH04207830A - Image audio transmitter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention is applicable to transmission systems mainly intended for low-speed, narrow-band voice transmission, such as general telephone lines and wireless communication lines, for example.
The present invention relates to a transmission device that transmits image data.

(Summary of the Invention) In a system that transmits images and audio by frequency division multiplexing, the side that sends and receives audio has a band elimination filter for removing the frequency band used by image data, and the The transmitting/receiving side has a band-pass filter that allows only the band used by image data to pass through so as not to affect the band used by audio, and a band-pass filter for separating or combining the image and audio data. By having a connection means and a frequency modulation/demodulation means for converting the image signal into an audio band and transmitting and receiving it as image data,
Images and audio are transmitted simultaneously without interfering with each other,
The optimal call signal strength (receiving state) is achieved by detecting the level of the received image signal, whose signal level changes depending on the state of the transmission path, and varying the signal level of the receiving means. The present invention relates to a transmission device configured to maintain the following.

(Prior art) In stand-alone telephones, etc., when the distance from the telephone office is long, a decrease in the volume of the call is detected by means for detecting a decrease in DC loop current, and the gain of the receiving circuit is varied (
Conventionally, efforts have been made to keep the volume constant using an amplifier.

(Problems to be Solved by the Invention) This will be described using a general telephone line as an example. When transmitting voice/data over a line, cable loss between the terminal and the central office,
In the case of telephones, even if the call signal level on the calling side is constant, the call volume on the receiving side will vary depending on the line connection, especially in the case of long-distance calls. The lower the side voice, the higher the rate of intelligibility decline. The present invention solves the problem of deterioration in call quality when transmitting audio and video using a method different from conventional methods. It is something to do.

(Means for Solving the Problems) - The present invention provides a signal amplitude of a modem signal (image data, amplitude is constant because it is a frequency modulation means) band-separated by a filter among image/audio signals to be multiplexed. Detecting,
By using means for varying the signal level of the receiving means, an optimum call signal strength (receiving state) can be maintained.

(Function) As a result, it is possible to make a call while transmitting an image on a general telephone line, etc., and it is also possible to maintain the reception level of the call quality almost constant regardless of the line condition.

(Embodiment) Hereinafter, an embodiment of the image and audio transmission device of the present invention will be described with reference to FIGS. 1 to 4.

FIG. 1 is a block diagram showing an embodiment in which the present invention is applied to an analog line. FIG. 2 is an explanatory diagram showing details of the image data signal level detecting means and the variable signal amplifying means of the receiving circuit in the present invention. FIG. 3 is an explanatory diagram of multi-frequency value modulation (MFM). FIG. 4 is a diagram showing the format of the transmitted/received image data signal.

In this example, multi-frequency value modulation (MFM)
This is a case where bit (64 gradation) image data transmission and simultaneous voice communication are performed, and the image data is 2000 to 2400H.
An example of frequency division multiplexing in the z band will be explained.

In FIG. 1, an image/audio transmission device serving as a terminal device connected to an analog line is configured as follows. 3
is the image memory. A video signal from the camera 1 is supplied to the image memory 3 after being converted into a digital signal of, for example, 6 bits per sample by the A/D converter 2, and image data for one image is written therein.

Also, the image data read out from the image memory 3 is D
/ Converted to an analog signal by the A converter 5 and sent to the display device 4
is supplied to

Then, image data is sequentially read out from the image memory 3 via the CPU 6 and supplied to the modem 7.

This modem 7 constitutes a multi-frequency value modulation/demodulation means, and is capable of dividing 6 bits of 164 gradations into frequencies used by image data at equal periodic intervals.

This modem 7 is provided with a modulation counter (not shown), and this modulation counter is supplied with 6-bit image data representing 64 steps (gray levels) from the image memory 3. It is counted down from a predetermined value in accordance with the data. In other words, equal time differences are given to the period of the square wave corresponding to each step.

In this case, the period corresponding to the first step is I/2000
Hz, the period corresponding to the 64th step is 172400
Hz. In other words, the frequency of the first step square wave is 2000Hz.

The frequency of the second step square wave is 2005H20,63
The frequency of the square wave at the 64th step is 2393 Hz, and the frequency of the square wave at the 64th step is 2400 Hz (as shown in FIG. 3A).

Unfortunately, the receiving modem section 7' of the modem 7 has an AGC circuit 7a,
It consists of a waveform shaping circuit 7b and a demodulation counter 7c (see FIG. 2). The waveform shaping circuit 7b is supplied with a voice band signal from the transmitting side via an analog line. This audio band signal is a sine wave signal obtained by passing the above-mentioned square wave signal through a band pass filter (BPF) 8 having a passband of 2000 to 2400 Hz, as will be described later. The waveform shaping circuit 7b reproduces the original square wave signal based on the zero crossing point of the sine wave signal.

The square wave signal from the waveform shaping circuit 7b is supplied to the demodulation counter 7cVC. As described above, the square wave signal has a period corresponding to the value (step) of the image data. In the demodulation counter 7c, a counting operation is performed during each cycle of the square wave signal, and the periodic power of each cycle of the square wave signal is calculated from the count value. The demodulation counter 7c outputs 6-bit image data having a value corresponding to the period, and this 6-bit image data is supplied to the image memory 3 via the CPU 6.

The square wave signal output from the modulation counter (not shown) of the modem 7 is passed through a band pass filter (BPF) 8 having a pass band of 2000 to 2400 Hz, and then sent to a 2-wire 4-wire converter 9 as an audio band signal. The supplied audio band signal becomes a sine wave signal as shown in FIG. 3BK.

The audio signal from handset I3 is 2000-2400Hz
The signal is supplied to the two-line and four-line converter 9 via a band-elimination filter (BEF) II that removes the band.

In the 2-wire/4-wire converter 9, the audio band signal from the bandpass filter 8 and the band-limited audio signal from the band-removal filter 11 are combined to form a transmission signal. This transmission signal is a frequency division multiplexed signal of a voice band signal and a voice signal.

The transmission signal from the 2-wire/4-wire converter 9 is supplied to the analog line through the dialer 10.

Next, the transmission signal supplied from the transmitting side via the analog line is supplied to the 2-wire 4-wire converter 9 through the timer 10.

The transmission signal from the 2-wire 4-wire converter 9 is passed through a bandpass filter 8.
A voice band signal is extracted from the voice band signal, and this voice signal is supplied to the modem 7. Then, as described above, the image data is demodulated from the audio band signal, and is supplied to the image memory 3 via the CPU 6.The audio signal is extracted from the filter 11, and this audio signal is supplied to the handset 13. Ru.

As described above, in FIG. 1, image data and audio signals are band-separated/synthesized by the band-pass filter 8 and the band-removal filter 11, and are transmitted to or received over the line as a frequency division multiplexed signal.

In FIG. 1, an image signal received via a line is not always received with a constant amplitude because the amount of signal attenuation varies depending on the transmission path. Therefore, the reception modem section 7
' is provided with an AGC circuit 7a (see FIG. 2) to ensure modem operation when receiving a weak signal. The level (amplitude) of the received modem signal received from the line and further passed through the bandpass filter 8 is detected by the level detection circuit i@14, and if the signal is weak, the amplification gain of the reception circuit is adjusted according to the signal level. A characteristic feature of the present invention is to perform an operation to compensate for a call (receiving call) during a weak signal by increasing the number of calls.

Its operation will be explained using FIGS. 2 and 4.

FIG. 4 shows a seven-way transmission format for image data that has been subjected to low-speed conversion (multi-frequency value modulation) for transmission over a line. Among the header information Dh provided before the image information Dv, the amplitude of the modem signal is measured using pilot information Dhp (multiple cycles of a single frequency). Bandpass filter (BPF) in Figure 2
The received data signal (analog signal) via the A/D '4 converter 14a is separated from the image data reproduction path.
is input. Here, the amplitude value is converted to digital data, and when the CPU 6 detects reception of a pilot signal from the modem signal demodulated and reproduced by the receiving modem section 7' on a different route, the output from the A/D converter 14a is The data is latched (+4b) L, and the output of the latch circuit +4b is converted to a continuous DC voltage level e by the D/A converter 14c.
Further, a variable gain amplifier 12 is provided at the speech reception output stage, which operates to reduce the amplification gain when the DC voltage e is high and to increase the amplification gain when the DC voltage Ee is low. As a result, when the volume during a call (receiving call) is low (the data reception level is also low), the output stage volume can be compensated for by increasing the gain of the output stage.

In the above-mentioned embodiment, the image data is 6 bits, but it can be similarly configured to have any number of focuses. Further, the frequency band used for the voice band signal is not limited to this.

In addition, in the above embodiment, transmission is performed using an analog line, but it is also possible to transmit image data and audio signals simultaneously using other transmission media. It is.

(Effects of the Invention) As described above, according to the present invention, when the line attenuation is large, the received image data is basically 17-frequency modulation (constant modulation), so the data is limited to the limit of data demodulation. Although it is simply determined by the S/N at the limit, the audio signal changes dynamically, so there is no possibility that a call may be heard or not depending on the amplitude, and the image and audio of the present invention Since the transmission device is configured to compensate for speech operations especially when the amount of attenuation in the line is large, it is possible to maintain optimal speech signal conservation (receiving state), and clear speech is always possible.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention applied to an analog line, and FIG. 2 is an explanatory diagram showing details of the image data signal level detection means and the variable signal amplification means of the receiving circuit in the present invention. , Figure 3 shows multi-frequency modulation (MFM)
FIG. 4 is a diagram showing the format of the transmitted/received image data signal. 1...Camera, 2...A/D converter, 3...Image memory, 4...Display device, 5...D/A converter, 6...CPU, 7...Modem, 7 '...Reception modem section, 8...Band pass filter (BPF), 9...
2-wire 4-wire converter, 10... dialer, 11... band rejection filter (BEP), 12... variable gain amplifier, 13... handset, 14... level detection circuit, D
v: image information, Dh: header information, Dph: pilot signal, Dhc: image control signal. Agent Patent Attorney Ume 1) Katsu (and 2 others)
1 2 63 64Figure 3

Claims (1)

[Claims] 1. In a device that frequency-division multiplexes image data and audio signals and transmits them simultaneously, a band elimination filter for removing the frequency band used by the image data is provided on the side that transmits and receives the audio signals. A band pass filter is provided on the side that transmits and receives the image data to pass only the band used by the image data so as not to affect the frequency band used by the audio signal, and each of the image and audio data and frequency modulation/demodulation means for converting image data into audio band signals and transmitting and receiving them as image data.As a communication means, the signal level changes depending on the state of the transmission path. What is claimed is: 1. A video and audio transmission device comprising means for detecting the level of a received image signal and varying the signal level of a receiving means to maintain an optimum call signal strength.