JPS6025172Y2 - signal receiving device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a signal receiving device, such as a facsimile receiving device, for demodulating signals modulated by a number of modulation methods.

When transmitting image signals using a facsimile receiving device, etc., the image signals are usually modulated by the DSB method or AM-PM-VSB method using a modem installed at the end of the line, and then transmitted. It will be done.

In addition, on the receiving side of the image signal, the image signal and its control signal, etc., are distinguished by which modulation method they are modulated using a phase matching signal at the start of transmission, and the image signal is demodulated. That's what I do.

FIG. 1 is a time chart for explaining signals with different modulation methods, and FIG. 2 is a block diagram of a conventional facsimile receiving apparatus.

DMO in the figure. VMO is DSB and VSB modulator, SMI
, 3M2. SDl, SD2 are switches, DDM, VDM
is a demodulator, 0°C is a carrier identification section, Konaka is a hybrid circuit, and C0NT is a control section.

Generally, a phase matching signal (shown in FIG. 1a) of a signal modulated and transmitted using the DSB method is formed by modulating a carrier signal of frequency f1 at a predetermined period t1 for a modulation period 110. There is.

For this reason, 1. When demodulating this received signal a, a filter having the frequency of the carrier signal in its pass band is used, and the detection unit α℃
Detect with.

Next, the control unit C0NT switches the switches SDI and SD2 for phase matching, and the demodulator DDM demodulates this signal.

In addition, the phase matching signal (shown in Figure 1) of the signal modulated and transmitted by the AM-PM-VSB method has a frequency f2
The carrier signal, CAR, is amplitude-modulated depending on the presence or absence of the signal, and is modulated to become a signal with a corresponding phase shift.

Therefore, when demodulating this received signal, the detection unit CDC detects that the signal of frequency f2 is received by a filter or the like, and the control unit C0NT selects the switch SDI,
Switch SD2.

Next, after demodulating the carrier by phase matching the carrier CAR in the demodulation circuit VDM, the received signal is multiplied by this carrier and full-wave rectified, resulting in a pulse signal whose level changes in three levels (as shown in Figure 1 d). ) is output.

In addition, when a facsimile machine or the like is driven unattended, it modulates the received signal using the received signal modulation method based on the carrier detected by the carrier detection unit, and sends a phase-matched signal to the opposing facsimile machine. The control unit C0NT controls the modulator D to send back a reception confirmation signal, etc.
Switches SMI and SM2 are driven to select MO1VMO. Therefore, a received signal and a signal modulated using the same modulation method are sent to an opposing facsimile device (not shown) via the hybrid circuit HYB.

However, these conventional receiving devices require a timer or the like to determine which modulation method the received signal has been modulated with, and to detect when the signal extracted by the filter continues for a predetermined period of time. , has the disadvantage of making the device complex and expensive.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a signal receiving apparatus that eliminates the above-mentioned drawbacks and easily detects a modulation method and demodulates a signal without requiring carrier signal identification.

In order to achieve the above object, the present invention uses a phase matching signal modulated by the DSB method, AM, and PM.

Focusing on the fact that the modulation period is different from the phase matching signal modulated by the VS dust modulation method, we first phase match and detect the cycle of the envelope of the received signal using the DSB method, and then generate the signal modulated using the DSB modulation method. This device operates a demodulation circuit for demodulating signals modulated by AM, PM, or VSB modulation methods that require a phase-matched carrier signal when a phase-matched carrier signal is detected. The details will be explained based on FIG. 3.

Components in the figure that correspond to those in Figure 2 are indicated by the same symbols.
CT is a counter, SWC is a switch controller, C1
is a clock generator, and A1-A3 are AND circuits.

That is, the signal received via the hybrid circuit HYB is input to the DSB demodulator DDM via the switch SD2 which is always connected to the positive terminal side.

The demodulator DDM performs envelope detection of the input signal, and the pulse signal subjected to the envelope detection is input to the control unit C0NT via the switch SDI.

The control unit C0NT resets the counter CT at the rising edge of this pulse signal.

The counter CT counts the clocks from the clock generator, and when it counts the numerical values "n", "m", and '"r99, it produces pulse outputs at the terminals n and my r, and outputs pulses to the ant gates AI and A2 and A3, respectively. Open.

These numerical values, n, m, and r, are each outputted as a pulse at a time corresponding to the modulation period of the received signal described above.

Therefore, AND circuit AI, A2. It is determined which gate has output from A3, and, for example, an AND gate, for example, A
If the output is from 1, switch control SW
C does not drive the switches SDI, SD2, and if the modulation period is other than the DSB modulation method, AND circuits A, 2. The switch controller SWC detects the output from A3 and switches the switches SDI and SD2 to the ■ terminal side.

In the demodulation circuit DM, a PLL circuit (not shown) is used to perform phase matching with the carrier and phase matching of the demodulation cycle, thereby reproducing the image signal following the phase matching signal.

As described above, according to the present invention, a signal receiving device that does not require a carrier signal identification circuit is realized.

[Brief explanation of drawings]

FIG. 1 is a time chart of signals with different modulation methods, FIG. 2 is a block diagram of a conventional signal receiving device, and FIG. 3 is a block diagram of an embodiment of the present invention. In the figure, C0NT is the control unit, HYB is the hybrid circuit,
0°C is the carrier identification section, DMD, VMO is the modulator, DD
M, VDM is a demodulator, SMI, 8M2. SDl, SD2
is a switch.

Claims (1)

[Scope of utility model registration request] At every first predetermined period, the first
and a second signal modulated by the VSf modulation method with a period different from the first predetermined period, and the modulation method of the signal is received. In a signal receiving device that demodulates a received signal in accordance with A signal detecting signal comprising detection means for detecting the period of the signal, and switch means for switching and supplying the received signal to a demodulation circuit for a signal modulated by the VSf modulation method based on the output of the detection means. Receiving device.