JPS6031380B2 - facsimile receiving device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a facsimile receiving apparatus that demodulates a received signal using synchronous detection, and particularly relates to a facsimile receiving apparatus that demodulates a received signal using synchronous detection.
(abbreviated as LL circuit).

Generally, a PLL circuit includes a phase comparator, a DC conversion circuit,
It is constructed using a voltage holding circuit, voltage controlled oscillator, etc.
This reproduces a carrier wave that has the same phase and period as the carrier wave of the image signal input to the facsimile receiving device.

This carrier wave regeneration operation needs to be completed before the image signal arrives, and it is also necessary to follow carrier wave fluctuations due to the influence of the line during the image signal period, and at the same time, during the period when the carrier wave is not present. , it is necessary to stop the operation and hold the state. In order to stop operation and maintain the state during the period when no carrier wave is present, the capacitance of the capacitor in the voltage holding circuit has been increased to cope with this problem.

However, depending on the circuit configuration of the voltage holding circuit, the power supply may be
When the capacitor is turned on, a random value of voltage may be charged to this capacitor. It became necessary to operate the circuit for a long time. However, as mentioned above, the PLL circuit of a conventional facsimile receiving device needs to reproduce a signal with the same phase and period as the carrier wave before the image signal arrives. , and a communication control signal having the same frequency as the carrier wave.

Communication control signals are used to control facsimile communication according to the sequence, such as confirming line establishment, confirming whether the transmit/receive state is possible, confirming the mutual ID, determining the transmit/receive mode notification, confirming the synchronization status, and confirming the completion of reception. It is a signal that is exchanged between transmitter and receiver for the purpose of communication.

Figure 1 shows CCI, which can be called standard medium-speed facsimile communication.
3 is a timing chart showing a communication control signal before sending out an image signal as described in TT Recommendation T-30.
As shown in FIG. 1, the communication control signals sent from the sending side to the facsimile receiving device before sending out the image signal are a GC signal and a phase signal. These GC signals and phase signals generally have the same frequency as the carrier wave of the image signal, so these two signals are used to operate the PLL circuit, so that the GC signal and the phase signal are in phase with the carrier wave of the image signal before the image signal arrives. Regenerate signals with the same period. FIG. 2 is a timing chart showing the relationship between the GI signal and the GC signal.

The GC signal is a signal that is sent for 1.5 seconds immediately after confirming the GI signal sent from the receiving side. C.C.
The transmission time of the communication format described in ITT Recommendation T-30 is 3 minutes, but recently a 2-minute mode version has been considered, and a signal of any frequency (dashed line A) is sent immediately after the GI signal.
Increasingly, the receiving side is sending out a GI signal that distinguishes between two modes by adding a GI signal.

In this case, in reality, only 0.79 minutes are sent to the receiving side. This is nothing but a reduction in the amount of time the PLL circuit operates before the image signal arrives, and as mentioned above, the capacitor of the voltage holding circuit is charged with a voltage that is far different from the predetermined voltage. In some cases, a signal having the same phase and period as the carrier wave of the image signal could not be completely reproduced before the image signal arrived. Further, FIG. 3 is a timing chart of phase signals.

Although the phase signal also has the same frequency as the carrier wave of the image signal, periods in which no carrier wave is present appear periodically, making it extremely difficult to determine the operation timing of the PLL circuit. The present invention has been made to solve the above-mentioned drawbacks, and in a facsimile receiving device, the communication control signal sent to the transmitting side is also input to the demodulation circuit of the facsimile receiving device to operate the PLL circuit. The present invention provides a facsimile receiving apparatus which reproduces a signal having the same phase and period as the carrier wave of the image signal completely before the image signal arrives.

The present invention will be explained below based on the drawings. FIG. 4 is a schematic diagram of a facsimile receiving apparatus according to an embodiment of the present invention. In FIG. 4, the area within broken line B indicates a demodulation circuit, and the area within broken line C indicates a PLL circuit. In the figure, 1 is a control circuit, which has a frequency detection function inside. 2 is a modulation circuit.

3 is a hybrid circuit, and when used ideally, the signal output from the modulation circuit 2 is sent only to the line from terminals 14 and 15, but in reality it is difficult to use it ideally, so the modulation circuit The signal output from 2 is input to both the line and the demodulation circuit.

4' is an AGC circuit, 5 is a waveform shaping circuit, 6 is a phase comparator in the PLL circuit, 7 is a gate circuit for switching the operation or holding of the PLL circuit, and 8 is a phase input via the gate circuit 7. A low-pass filter (hereinafter referred to as L) converts the output of the comparator into a DC component and also functions as a voltage holding circuit.
9 is a voltage controlled oscillator (hereinafter referred to as PF) that changes its oscillation frequency depending on the output voltage level of LPF 8.
(abbreviated as VCO), whose nominal frequency is switched by the control circuit 1.

10 is a synchronous detection circuit, 11 is a signal processing circuit, and 12 is a recording circuit, the operation of which is controlled by the control circuit 1.

In the facsimile receiving device having the above configuration, the PLL
The operation of making the output signal of the circuit C the same phase and period as the carrier wave of the image signal before the image signal arrives will be explained. The description of this embodiment will proceed in accordance with the communication format of the international standard for facsimile long-distance machines described in CCITT Recommendation T-30. First, turn on the power of the facsimile receiving device.

At this time, the power supply voltage of the amplifier 8b in the LPF 8 is ±
If the voltage is 12V, the voltage holding capacitor 8d has 11V.
A voltage ranging from 2V to -12V is randomly charged. Assuming that the voltage charged in the capacitor 8d is 112V, the LPF 8 will output while maintaining this voltage level. As a result, the VCO 9 outputs a signal having a frequency completely different from the nominal frequency. Subsequently, the facsimile receiving device enters a standby state. Next, when the sender calls the facsimile receiver, the ring tone establishes a line between the sender and the receiver. After the line is established, a communication control signal (hereinafter abbreviated as CED signal) notifies the calling party that a facsimile terminal exists on the called party.
is transmitted from the receiving side to the sending side. The frequency of this CED signal is 2100 days, which is almost equal to the frequency of the input image signal. Further, this CED signal is output from the modulation circuit 2 to the hybrid circuit 3 by a control signal from the control circuit 25, and is sent from the hybrid circuit 3 to the transmission side via a line. At the same time, the CED signal is also output from the hybrid circuit 3 to the demodulation circuit B. At this time, the gate circuit 7, which has been closed until now, is opened for the first time in response to a control signal from the control circuit 1. The CED signal input to demodulation circuit B is
After passing through the C circuit 4, it is divided into 20,000 parts, one of which passes through the waveform shaping circuit 5 and is input to the PLL circuit C, and the other part is input to the synchronous detection circuit 101.

Since the gate circuit 7 of PLL circuit C is open, this C
It operates using the ED signal.

In other words, it operates to become a signal with the same phase and same period as this CED signal. First, the phase comparator 6 is connected to the waveform shaping circuit 5.
The output signal of the VCO 9 and the output signal of the VCO 9 are compared in phase to output a phase error signal. By the way, since the VCO 9 outputs a signal having a frequency that is significantly different from the nominal frequency as described above, this phase error signal initially shows a large error. This phase error signal passes through the gate circuit 7 and is input to the LPF 6.
It operates to normalize the DC voltage level held by PF8 to a predetermined voltage level (for example, OV). However, the capacitor 8d in the LPF 8 is charged with a large voltage (for example, 112 V) and does not suddenly drop to a predetermined voltage level (for example, ±OV), but the duration of the CED signal is 2.6 seconds. Because of the above, the output DC voltage level of the LPF 8 can sufficiently reach the predetermined voltage level during this period. Therefore, the VCO 9 outputs a signal having the same frequency (2100 Hz) as the CED signal. In the above description, the frequency of the signal output from the PLL circuit C is approximately equal to the frequency of the carrier wave of the image signal, and it is only necessary to correct phase and period errors. Next, the receiving side issues a CI signal informing the model and function.

This GI signal is also input to the demodulation circuit, but since the frequency of the GI signal is 1850 Hz, the control circuit 1 closes the gate circuit 7 and does not operate the PLL circuit, leaving it in a holding state.
Next, in response to the GI signal sent from the receiving side,
A GC signal is output from the transmitting side to notify the mode in which communication is possible.

This GC signal generally has the same frequency (2100Hz) as the carrier wave of the image signal, is modulated by the same modulation circuit, and passes through the same line, so the CC signal has the same phase and period as the carrier wave of the image signal. becomes. Therefore, when a GC signal is input to the receiving side, the control circuit 1 opens the gate circuit 7 and operates the PLL circuit C using the GC signal. As a result, the phase and period of the output signal of the PLL circuit C are corrected within a short time, so that the output signal can have the same phase and period as the carrier wave of the box signal. Note that when the GC signal arrives at the receiving side, the receiving device receives the GI signal, and when the GI signal arrives at the receiving side, the receiving device
Stop sending the I signal. In addition, following the GC signal, the transmission side transmits a signal at the same frequency as the carrier wave of the image signal (2100Hz).
) is sent out.

The receiving side reproduces this phase matching signal and sends it to the recording device 12.
match the phase of the regenerated phase matching signal. Since the signal output from the PLL circuit C has the same phase and the same period as the carrier wave of the image signal, the phase matching signal can be reproduced by the synchronous detection circuit 1 without providing an extra phase matching signal reproducing circuit.
0 and the signal processing circuit 11, sufficient reproduction is possible. It is also possible to operate the PLL circuit C during the period of . There are various facsimile transmitting devices and receiving devices, and the GC signal modulation circuit and the image signal modulation circuit are different on the transmitting side. In some cases, the modulation circuit for the GC signal and the modulation circuit for the image signal may be different on the receiving side, and the output signal of the PLL circuit during the GC signal period may be completely in phase and period with the carrier wave of the image signal. There will never be a match.

However, the phase signal sent from the transmitting side during this phase signal period is always modulated by the same modulation circuit as the image signal, and demodulated by the same demodulation circuit, so the phase signal and the carrier wave of the image signal have a period of and the phases are completely matched. Therefore, if the PLL circuit is operated during this phase signal period,
In most facsimile receiving apparatuses, a signal having the same phase and period as the carrier wave of the image signal is obtained at the output of the PLL circuit before the image signal arrives. However, since it is difficult to operate the PLL circuit for the phase signal as described above, it is preferable to use the same modulation circuit and demodulation circuit for the GC signal and the image signal as in this embodiment. . On the receiving side, when the phase matching is completed, the receiving device sends out a CFR signal indicating that the phase matching has been completed.

At this time, the PLL circuit C is in a holding state. Only after receiving this CFR signal does the transmitting side begin transmitting the image signal.
Then, on the receiving side, in the synchronous detection circuit 10', P
By using a signal having the same phase and the same period as the carrier wave of the image signal reproduced by the LL circuit C, normal synchronous detection can be performed from the beginning of the image signal.

The above explanation has been made according to the transmission format described in CCITT Recommendation T-30.

Therefore, the carrier waves of the CED signal and the image signal were the same. However, general facsimile machines have CCITT
In addition to the transmission mode complying with Recommendation T-30, each facsimile manufacturer has its own transmission mode, and in these transmission modes, the frequencies of the CED signal and the carrier wave of the image signal may differ. In this case, the nominal frequency of the VCO may be switched by a control circuit. That is, when transmitting the CED signal, the nominal frequency of the VCO is made to match the frequency of the CED signal, the control voltage level of the VCO output from the LPF is set to a predetermined voltage level, and then a communication control signal having the same frequency as the carrier wave of the image signal is sent. If the nominal frequency of the VCO is switched to the same frequency as the carrier wave of the image signal when the image signal arrives, a signal having the same phase and period as the carrier wave of the image signal can be reproduced before the image signal arrives. As described above, according to the present invention, in a facsimile receiving apparatus, a communication control signal to be transmitted to the transmitting side is inputted into the demodulation circuit and added to the demodulation circuit before the arrival of the image signal, and the PLL circuit in the demodulation circuit is operated. , no matter what voltage is charged to the capacitor of the voltage holding circuit in the PLL circuit when the power is turned on, it can be set to a predetermined voltage before it is sent from the receiving side, so the next receiving When the PLL circuit is operated for a transmission side communication control signal having the same frequency as the carrier wave of the image signal that has arrived at the device, a signal having the same phase and same period as the carrier wave of the image signal can be reproduced in a short time.

Therefore, before the image signal arrives, it is in phase with the carrier wave of the image signal.
Since signals of the same period can be reliably reproduced, normal synchronous detection can be performed from the beginning of the image signal, and a normal recorded image can be reproduced. Brief Description of the Drawings Figure 1 is an explanatory diagram of communication control signals, Figure 2 is a timing chart of GI signals and GC signals, Figure 3 is a timing chart of phase matching signals, and Figure 4 is an explanatory diagram of communication control signals.
The figure is a block diagram of a facsimile receiving apparatus according to an embodiment of the present invention.

1...Control circuit, 2...Modulation circuit, 3
...Hybrid circuit, 6...Phase comparator, 7...Gate circuit, 8...LP
F, 9...VC○, 1 0...Synchronous detection circuit, B...Demodulation circuit, C...PL
L circuit, 8d""" capacitor.

Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. A phase locked loop means for regenerating the carrier wave of the input modulated signal, a demodulating means for performing synchronous detection using the regenerated carrier wave outputted by the phase locked loop means, and and control means for operating the phase locked loop means when the communication control signal is input to the phase locked loop means. A facsimile receiving device characterized by: