JPH0122790B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a communication terminal device that modulates image information for communication.

[Prior art]

As such communication terminal devices, facsimile devices have come to be widely used as means for transmitting image information through telephone lines.

Figure 1 is a block diagram showing the electrical circuit of a conventional facsimile transmitter, Figures 2a and b are waveform diagrams of image signals (the horizontal axis is time), and Figures 3a to d are filter diagrams. The band characteristics (the horizontal axis is the frequency) are shown respectively.

In FIG. 1, an image sensor 1 can scan a document 1a, convert changes in optical density into changes in electrical level according to information on the document 1, and output the converted changes. The image signal output from the image sensor 1 can be represented by the signal 1b in Fig. 2a, and the signal 1b is expressed as 2-
The signal is input to the three-value conversion circuit 2. The 2-3 value conversion circuit 2 converts a white signal (level "1") and a black signal (level "0") representing white information on the original 1a,
As the scanning progresses, each time the white signal changes from a white signal to a black signal and then becomes a white signal again, the polarity is inverted and the ternary signal 2a shown in FIG. 2b is output. A low-pass filter (hereinafter referred to as LPF) 3 inputs the ternary signal 2a and limits it to an appropriate band (usually a filter having the characteristics shown in FIG. 3a of about ₀ =1.6 kHz is used). On the other hand, a carrier signal used for modulating the image signal is generated by a carrier generation circuit 6 (usually at a frequency of 2100 Hz). When the switch 7 is connected to the contact 7a side as shown, the carrier generation circuit 6 receives a signal from the control circuit 5, outputs the carrier signal, and sends it to the modulator 4 via the switch 7. The modulator 4 modulates the image signal input from the LPF 3 with the carrier signal, but at this time, the output of the modulator 4 is AM-PM-DSB (Amplitude
Modulation―Pulse Modulation―Double Side
Band) signal, which has band characteristics as shown in FIG. 3b.

VSB (Vestigial Side Band) filter 8 is
Since the band characteristics shown in FIG. 3c, that is, the output becomes 1/2 at the carrier frequency _c , and the characteristics are point symmetrical to the output 1/2 point on both sides of _c , the modulator 4
The above AM-PM-DSB signal input from AM-
It is converted into a PM-VSB signal and has the output characteristics shown in Figure 3d.
limited by figure c].

In this way, a VSB filter that partially passes the residual sidebands of the modulated signal is applied to the modulator 4.
The signal shown in FIG. 3b inputted from the converter is changed into the signal shown in FIG. 3d and output. (It should be noted that the content explained above is valid not only in the case of the AM-PM modulation method but also in the case of the AM modulation method). The output of VSB filter 8 is
It is sent out to the line 10a by an NCU (abbreviation for Net Control Unit and called a network control circuit) 9a, and image information can be transmitted. On the other hand, in a facsimile device, a "tonal signal" is generated to instruct the transmission procedure of the image information, but when the switch 7 is switched to the contact 7b side in FIG. A control signal is input from 5 and a desired tonal signal is output. The tonal signal is inputted to the LPF 11 via the contact 7b of the switch 7, and is band-limited. Then, it is sent to the line 10a via the NCU 9a. Furthermore, since the tonal signal is connected to one input section of the AND gate 13,
If the operator wishes to confirm the completion of a transmission, the occurrence of an error, a telephone call request, etc. using a tonal signal, a high level signal is applied to the other input section (input terminal 12) of the AND gate 13. Just leave it there. That is, the tonal signal outputted from the carrier generation signal 6 passes through an AND gate 13, is amplified by an amplifier 14, and can be made into sound by a sounding element 15. However, if the above-mentioned sounding body 15 is used as a buzzer, only continuous or intermittent sounds such as "pooh" or "poo-poo" consisting of a substantially constant frequency can be generated, so that the operator can distinguish the meaning of the signal sound. Things are difficult. Further, when the sounding body 15 is a speaker, there is a drawback that the sound is hard and unpleasant because it is driven by a square wave signal.

FIG. 4 is a block diagram showing the electrical circuit of a conventional facsimile receiver. In FIG. 4, the image signal transmitted from line 10b is
AGC (Automatic Gain Control) via NCU9b
(also called automatic gain control device) Circuit 1
6 and becomes a level value suitable for demodulation. The demodulator 17 demodulates the signal input from the AGC circuit 16 , but part of the output of the AGC circuit 16 passes through the carrier extraction circuit 18 to extract a carrier (carrier wave), and the extracted carrier is input to the demodulator 17 do. The demodulated signal exhibits a curve 22a below the carrier frequency _c in the band characteristics shown in _FIG .
Therefore, the output of the demodulator 17 has the output characteristics shown by curves 22a and 22b in FIG. 5a. In this way, since the output of the demodulator 17 includes an extra high frequency component (the part of the curve 22b) in addition to the demodulated signal, the LPF 19 removes the high frequency component and extracts only the part of the curve 22a.

However, since the LPF 19 has the characteristics shown in FIG. 3a, the output characteristics of the signal output from the LPF 19 are not the curve 23a in FIG. 5b but the curve 24 (broken line). Therefore, the sharpness of the recorded image is lowered compared to the characteristic of the curve 23a.
The output of the LPF 19 is converted back to the waveform shown in FIG. Then, recording is performed by a recording means (not shown). However, if the transmitter and receiver are separated as shown in FIGS. 1 and 4, there is a drawback that circuits that can be used in common (for example, modulators (demodulators) 4 and 17) must be separately provided.

Furthermore, if a VSB filter for image information and a low-pass filter for tonal signals are provided separately as in the past, the configuration of the device will become complicated.

Therefore, it is conceivable to filter the tonal signal using a filter for image information to simplify the configuration of the device.

However, if the filter for image information filters tonal signals of a plurality of frequencies, the signal level of the tonal signal of high frequency will become low due to the characteristics of the filter for image information.

〔the purpose〕

An object of the present invention is to eliminate the above-mentioned problems, and also to allow a filter means for filtering image information to also filter a control signal. The objective is to maintain a constant signal level regardless of frequency.

〔Example〕

An embodiment of the present invention will be explained below with reference to the drawings.

FIG. 6 is a block diagram showing the electric circuit of the facsimile apparatus of this embodiment.

In FIG. 6, the image sensor 25 (for example, a solid-state image sensor such as a CCD can be used) is the original 25.
A is scanned, and changes in optical density are converted into changes in electrical level according to information on the original document 25a, and the converted changes are output. The image signal output from the image sensor 25 can be represented by the signal 1b in FIG. The 2-3 value conversion circuit 26 inverts the polarity each time the white signal becomes a white signal again after passing through the black signal as the original 25a is scanned, and converts the 3-value signal 2a shown in FIG. 2b. Output. On the other hand, the amplitude control circuit 28
is a circuit for keeping the output level of a tonal signal, which will be described later, constant regardless of the frequency, and is a circuit for making the output level of a tonal signal constant regardless of the frequency. Then, the level of the ternary signal 2a is adjusted. In other words,
In the AM-PM-VSB method (so-called G class of CCITT standard) facsimile equipment,
The tonal signals of 462Hz, 1100Hz, 1650Hz, 1850Hz, and 2100Hz are divided into respective levels l ₁ , l ₂ , l ₃ , l ₄ ,
l ₅ becomes the relationship l ₁ l ₂ > l ₃ > l ₄ > l ₅ . The above-mentioned amplitude control circuit 28 is thus a circuit that keeps the tonal signal output from the VSB filter 35 constant at each frequency in order to prevent the output level from decreasing at high frequencies and resulting in an unnatural sound. It is.
FIG. 8 is an internal configuration diagram of the amplitude control circuit 28.
In FIG. 8, the input signal _E1 is input to the negative input terminal (-) of an operational amplifier 28a (operational amplifier) via an input resistor _R1 . Since the positive input terminal (+) of the operational amplifier 28a is grounded, the potential of the negative input terminal (-) is "0" under normal operating conditions.
A feedback resistor R ₂ , a resistor R ₃ disconnected by a switch 46, and a resistor R ₄ disconnected by a switch 47 are connected in parallel between the negative input terminal (-) and the output terminal of the operational amplifier 28a. By operating switches 46 and 47, operational amplifier 28 is
The feedback resistance of a can be changed. Therefore,
The ratio E ₂ /E ₁ of the output E ₂ and the input E ₁ , that is, the gain G, is determined by switching the switches 46 and 47 (turning the switches 46 and 47 OFF-OFF, ON-OFF, OFF-ON,
The level of the DC signal output from the control circuit 27 can be changed. As a result, the levels l ₃ , l ₄ , l ₅ shown in FIG. 7 are changed to the level l ₁
It is possible to make the level approximately equal to (l ₂ ).

The output signal whose amplitude has been controlled by the amplitude control circuit 28 is input to an LPF 29 (low pass filter). The LPF 29 is a filter having the band characteristics shown in FIG. 3a. The switch 30 is the contact 30a
, the output of the LPF 29 is input to the modem 34 (modulator/demodulator) and modulated. On the other hand, when the switch 31 is connected to the contact 31a side, the carrier generation circuit 41 inputs the control signal from the control circuit 40 and outputs a 2100 Hz carrier signal. The carrier signal is input to the modem 34 via the contact 31a of the switch 31. modem 34
Since the DC signal input from the LPF 29 is modulated by the carrier signal, the fundamental wave component of the output signal matches the frequency of the carrier signal. High frequency components of the image signal modulated in this manner are removed by a VSB filter 35 (band characteristics shown in FIG. 3c). When the switch 32 is connected to the contact 32a side, the
The output of the VSB filter 35 is sent to the telephone line 39 via the NCU 38, and image information is transmitted. On the other hand, when transmitting a tonal signal, a control signal input from the control circuit 40 is used to transmit signals from the carrier generation circuit 41 to 462Hz, 1100Hz, 1650Hz, 1850Hz,
Outputs the desired tonal signal within the 2100Hz signal. The tonal signal is sent to the contact 31 of the switch 31.
The data is input to the modem 34 via a. Since the modem 34 modulates the DC signal from the control circuit 27, which is a DC signal generation circuit, by the tonal signal,
The fundamental wave component of the output signal matches the frequency of the tonal signal. High frequency components of the thus generated tonal signal are removed by a VSB filter 35 (band characteristics shown in FIG. 3c). The tonal signal outputted from the VSB filter 35 is amplified by the amplifier 36 and output to the speaker 37 when the switch 33 is turned on. speaker 37
Since the signal from which high frequency components have been removed by the VSB filter 35 is input to the input signal, the sound of the tonal signal becomes soft and easy to hear.

Next, when using the circuit of FIG. 6 for a receiver, the switches 30, 31, and 32 are connected to the contacts 3
a, 31a, 32a to contacts 30b, 31b, 3
Switch to side 2b. Image information input from the line 39 is input to the AGC circuit 42 via the NCU 38. The signal amplified to an appropriate level by the AGC circuit 42 is input to the modem 34 via the contact 30b of the switch 30, and the signal input to the carrier extraction circuit 43 is input to the modem 34 via the contact 31b of the switch 31. do. The modem 34 operates as a modulator during transmission, but can be used as a demodulator during reception. In other words, since modulation and demodulation can be achieved by multiplying the modulated signal and the demodulated signal by a carrier, in the case of a transmitter/receiver, the modulator itself can be used as a demodulator. Incidentally, a modem (MODEM or MOdulation and DEModulation) is given this name because it performs modulation and demodulation. The output characteristics of the signal demodulated by the modem 34 are shown in FIG. 5a, and when this output is input to the VSB filter 35 having the characteristics shown in FIG. 3c, the output characteristics are shown by curves 23a and 23b in FIG. 5b. characteristics can be obtained.
(Curves 23a and 23b are separated by carrier frequency _c ). Here, the curve 23a is a necessary image signal, and the curve 23b is an unnecessary high frequency component. Although there is a possibility that the image quality of the recorded image may deteriorate in the portion of the curve 23b, since the level is low, it can be said that there is almost no effect. Rather, like a conventional facsimile machine, the LPF has the characteristics shown in Figure 3a.
(low pass filter), curve 24
As shown by the broken line, the high frequency components in the image signal decrease, and the clarity of the recorded image decreases. However, in the facsimile machine of this embodiment,
By using a VSB filter, clear recorded images can be obtained. VSB filter 35
The signal from which high frequency components have been removed is sent to the 3-binary conversion circuit 4 via the contact 32b of the switch 32.
4 (generally using a full-wave rectifier circuit). The 3-2 direct conversion circuit 44 is the 3-2 direct conversion circuit 44 shown in FIG. 2b.
The value signal is converted into a binary signal shown in FIG. 2a and outputted to the signal line 45, and recorded by a recording means (not shown). In this way, in the configuration of the facsimile apparatus of this embodiment shown in FIG.
The modulation (demodulator) 4, 17 of FIG.
The VSB filter 35 also serves as the VSB filter 8, LPF 11, and LPF 19 in FIGS. 1 and 4,
Since the NCU 38 serves as the NCUs 9a and 9b in FIGS. 1 and 4, the device can be made smaller and the cost can be reduced. Furthermore, by using a VSB filter during reception, the quality of recorded images can be improved.

Note that the above description of reception is related to the reception of image signals, but the reception of tonal signals will be explained separately.

〔effect〕

As described above, according to the present invention, a plurality of control signals each having a different frequency are filtered by the filter means for communication information, so the configuration can be simplified, and moreover, the filter means for communication information filters a plurality of control signals, each having a different frequency. Even when the control signal is filtered, it is possible to output a control signal with a stable signal level regardless of the frequency of the control signal without deteriorating the communication information.

[Brief explanation of drawings]

Figure 1 is an electric circuit configuration diagram of a conventional facsimile transmitter, Figure 2 a and b are waveform diagrams of image signals, Figure 3 a is a characteristic diagram of a low-pass filter, and Figure 3 b is a characteristic of a modulated signal. Figure 3c is a characteristic diagram of the VSB filter, Figure 3d is a characteristic diagram of the signal output from the VSB filter, Figure 4 is an electrical circuit diagram of a conventional facsimile receiver, and Figure 5a is demodulation. Fig. 5b is a characteristic diagram of the signal output from the low-pass filter or VSB filter after demodulation, Fig. 6 is an electric circuit configuration diagram of the facsimile device of this embodiment, and Fig. 7 is a tonal signal. FIG. 8 is a circuit diagram showing the inside of the amplitude control circuit. In the figure, 25...imaging device, 25a...document, 26...2-3 value conversion circuit, 27, 40...control circuit, 28...amplitude control circuit, 29...low-pass filter, 30-33, 46, 47...switch ,3
4...Modem, 35...VSB filter, 36...Amplifier, 37...Speaker, 38...NCU, 39...Telephone line, 41...Carrier generation circuit, 42...AGC
Circuit, 43... Carrier extraction circuit, 44... 3-binary conversion circuit, 45... Signal line, 28a... Operational amplifier.

Claims (1)

[Claims] 1. An image information generating means for generating image information; a control signal generating means for generating a plurality of control signals each having a different frequency for instructing a transmission procedure of image information; a modulation means for modulating; a filter means for filtering the image information modulated by the modulation means with a frequency characteristic suitable for the band; a means for generating a direct current signal; and a means for generating the control signal by the filter means. and control means for performing gain control according to the frequency of the control signal to be filtered when filtering the control signal, and the control signal generated by the control signal generating means is transmitted to the modulating means as a carrier signal of the modulating means. the filter means filters the control signal by modulating the DC signal with the modulation means; A communication terminal device characterized in that gain control is performed to make the signal level of the control signal output from the filter means constant regardless of each frequency. 2. The communication terminal device according to claim 1, further comprising means for outputting the control signal output from the filter means as sound.