JPS6242393B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a carrier wave regeneration circuit, and more particularly to a carrier wave regeneration circuit for a demodulator that needs to regenerate a carrier wave when demodulating a signal transmitted on a receiving side in data transmission such as facsimile.

AM-PM-VSB modulation is a modulation method in facsimile that regenerates and demodulates a carrier wave.
This modulation method uses standard A4
It was developed for the purpose of shortening the transmission time, which conventionally required about 6 minutes, to transmit an image signal in about 3 minutes. However, on the sending side, AM−PM−
In order to obtain a VSB-modulated image signal as a reproduced image signal on the receiving side, a carrier wave regeneration circuit, which was not necessary in the conventional 6-minute transmission facsimile, became an essential component.

FIG. 1 shows a block diagram for reproducing both signals in the AM-PM-VSB modulation system, and FIG. 2 shows the operating waveforms of each part in FIG. 1 correspondingly. Referring to Figure 2,
The operation shown in FIG. 1 will be explained in principle. The AM-PM-VSB modulated signal a (drawn somewhat simplified in the drawing for clarity) applied to the received signal input port 1 is applied to the carrier recovery circuit 2 and is also applied to the multiplier 3. It will be done. The carrier wave reproducing circuit 2 reproduces the carrier wave b based on this signal a. On the other hand, the multiplier 3 uses the carrier wave b and the
The AM-PM-VSB modulated signal a is multiplied to obtain a multiplied output signal c. This multiplied output signal c is inputted to a low-pass filter 4 to obtain a ternary image signal d.
By applying the value image signal d to the signal restorer 5, a reproduced image signal e can be obtained at the reproduced image signal output port 6.

Generally, data transmission devices such as facsimile machines use telephone lines to communicate documents between each other, but the electrical characteristics of these telephone lines have a significant effect on the quality of the reproduced image signal on the receiving side. . The electrical characteristics of telephone lines mainly include frequency characteristics,
There are delay characteristics and jitter, and compensators for these two characteristics are commercially available. However, there is no device that can compensate for jitter. Jitter here refers to a phenomenon in which "fluctuations" occur in the signal received at the receiving end when an electrical signal of a certain single frequency is applied to a telephone line and transmitted. If such a jittery (“fluctuation”) AM-PM-VSB signal were to be demodulated, black would appear where it should have been white on a facsimile machine, or conversely, black would appear where it should have been black. If white appears, the information will be reproduced incorrectly.

In FIG. 3, the state of reproduction of the image signal of the AM-PM-VSB signal in which jitter has occurred is shown as a' to e' corresponding to a to e in FIG. 2, respectively. Figure 3 a' shows AM-PM-VSB with 90° jitter in some parts.
b' is a carrier wave reproduced from the signal a'. As will be described later, this recovered carrier wave b' does not respond to such jitter because the response time constant of the phase comparison circuit used in the carrier wave recovery circuit is increased. Therefore, the signal containing jitter
When a' is multiplied by a carrier wave that does not respond to jitter, a multiplied output signal c' is obtained, and when this signal c' is passed through the low-pass filter 4 shown in FIG. 1 to extract the low frequency component, a ternary image signal is obtained. d' is obtained, and this ternary image signal d' is applied to the signal restorer 5 to restore the image signal, as shown in Fig. 3 e', and the difference is obvious when compared with Fig. 2 e. It is. In other words, the part where the 90° jitter occurs is reproduced as black, even though it should originally be white.

In this way, data transmission equipment such as facsimile machines using AM-PM-VSB modulation method has significantly shortened transmission time, but because carrier wave regeneration circuits are essential components, This has led to the drawback that the quality of the received and reproduced image is greatly degraded due to the jitter.

Therefore, the main object of the present invention is to provide a carrier wave recovery circuit that can overcome the above-mentioned drawbacks.

In summary, this invention generates a first pulse at a predetermined position of an input signal in a carrier wave regeneration circuit of a demodulator of a data transmission device, and this pulse can also be voltage-controlled and has a frequency N times that of the carrier wave. sampling an oscillation signal of an oscillating self-excited oscillator, integrating this sampling result and applying the integrated output to the voltage controllable self-excited oscillator to synchronize the phase of the input signal and the oscillation signal of the oscillator; A phase comparison is performed between the phase-synchronized oscillation signal and a second pulse generated at a predetermined position of the input signal, the oscillation signal is further corrected by the phase comparison output, and this correction signal is sent to the comparison circuit. The carrier wave is regenerated by modulating the modulated signal and dividing the frequency of this modulated signal by 1/N.
This is a carrier wave regeneration circuit that shifts the phase of a carrier wave in a portion of an input signal where jitter occurs by the amount of jitter.

The above objects and features of the present invention will become more apparent from the following detailed description with reference to the drawings.

FIG. 4 is a block diagram of a carrier wave recovery circuit showing an embodiment of the present invention, and FIG. 5 shows waveforms of various parts of FIG. Note that FIG. 4 includes a conventionally used phase synchronization circuit. Below, in order to facilitate understanding of this invention, these will be explained together.

The noise component of the AM-PM-VSB modulated signal a' partially containing jitter is removed by the bandpass filter 21, and a delay of .DELTA.t is generated, as shown in, for example, a' and g in FIG. The AM-PM-VSB modulated signal g from which noise has been removed is given to the first single pulse generator 22, and an appropriate pulse width is set at the intersection between the falling edge of each cycle of the signal g and the ground potential. A rectangular pulse h is generated. On the other hand, the self-excited sawtooth wave oscillator 25 generates a sawtooth wave i with an amplitude of A (volt) above and below the ground potential, and a frequency twice the carrier frequency c. h and the phase comparator 23
give to This phase comparator 23 obtains a phase error signal j by sampling the sawtooth wave i with a pulse h. Then, this phase error signal j is applied to an integrator 24 with a large time constant to obtain an integral output k. This integrated output k is applied to the self-excited sawtooth wave oscillator 25. Therefore, in this self-excited sawtooth wave oscillator 25, the oscillation frequency is changed so that the integral output k becomes zero, that is, the phase error becomes zero. In this way, a sawtooth wave having a frequency twice the carrier frequency c, which is phase-locked in synchronization with the carrier wave, is obtained. Circuit 21 explained above
~25 is a commonly used phase-locked circuit.By the way, if you divide this sawtooth wave by 1/2 to create a square wave with a duty of 50%, for example, as shown in Figure 3.
A carrier wave as shown in b' can be obtained.

Now, the jitter-containing AM-PM-VSB modulated signal a' that has entered the received signal input port 1 is also provided to the second single pulse oscillator 26. This second single pulse oscillator 26 generates a rectangular pulse l at the intersection of the falling edge of the waveform of the input signal a' and the ground potential. Then, this pulse l and the phase-locked sawtooth wave are applied to a phase error detector 27,
The phase-locked sawtooth wave is sampled with a pulse l to obtain a phase error voltage m. Further, by adding the phase-locked sawtooth wave and the phase error voltage m to a subtractor 28 and subtracting the phase error voltage m from the phase-locked sawtooth wave i, a modulated sawtooth wave n can be obtained. Can be done. By adding this modulated sawtooth wave n to the comparator 29 and performing level discrimination using the ground potential, a level discrimination output p is obtained. Here, the subtracter 28 and the comparator 29,
This means that the sawtooth wave i, which is the output of the sawtooth wave oscillator 25, is phase-modulated by the phase error voltage m, which is the output of the phase error detector 27. This signal p is 1/
In addition to the 2-frequency divider 30, if the frequency is divided by 1/2 at the rising edge of the pulse of the signal p, the phase of the regenerated transmission corresponding to the part where jitter has occurred is shifted by the amount of jitter, as shown in Fig. 5. A jitter-corrected carrier wave can be obtained as shown as signal b''.

Jitter-corrected carrier wave b″ and AM shown in Figure 5
-PM-VSB When the modulated signal a' is multiplied by the multiplier 3 shown in Fig. 1, the multiplied output signal is obtained as shown in Fig. 5.
c'', and a reproduced image signal e'' is obtained in exactly the same way as the principle explained in FIG. 1. Furthermore, in the signal c in Fig. 2, the signal c' in Fig. 3, and the signal hc'' in Fig. 5, the ground potential portion is reproduced as black, and the portion with a signal only on the positive or negative side is reproduced as white. Please note that the third
If you compare the reproduced image signal e′ in the figure and the same e'' in FIG. 5, the difference is obvious, and the reproduced image signal
e'' is similar to the reproduced image signal e in FIG. 2, and it can be seen that no erroneous reproduction has occurred.

Note that in the above embodiment, the sawtooth wave oscillator 25
Although the oscillation frequency of the carrier wave is twice the frequency c of the carrier wave, it is not limited to twice, and it is of course possible to set the oscillation frequency to N parts (N is a positive integer). The frequency divider 30 may also be a 1/N frequency divider. This is similar to the fact that a normal phase-locked circuit can be constructed with an oscillation frequency that is an integral multiple of the input signal. Note that changing the value of N does not fundamentally affect the operation, so
It is determined by the ease of making the oscillator, the required frequency, etc.

Further, although the waveform of the oscillator 25 is shown as a sawtooth wave in the above embodiment, it may be a square wave oscillator, for example. In this case, the same operation can be achieved by using a phase comparator 23 that compares the phases of the rectangular pulse h and the square wave.

Further, in the above embodiment, the pulse h and the pulse l are generated at the intersection of the falling edge of each cycle of the input signal and the ground potential, but the generation point of the pulse h and the pulse l is set at the intersection point of the rising edge and the falling edge of each cycle of the input signal and the ground potential. There is an advantage that more accurate jitter correction can be achieved if pulses are generated at .

Furthermore, although the subtracter 28 and the comparator 29 constitute a phase modulator in FIG. 4, it is also possible to directly constitute a phase modulator to perform jitter correction.

In addition, in the above embodiment, the input signal is AM-PM-
Although the explanation has been given using a VSB modulated signal as an example, it goes without saying that the present invention can be similarly applied as long as the input signal does not sufficiently contain a carrier component, that is, a carrier suppressed modulated signal.

As described above, according to the present invention, when data is transmitted using a commercial line such as a telephone line, the jitter that occurs in the line is compensated for, thereby greatly improving the reliability of reproduction of the received signal. .

[Brief explanation of the drawing]

FIG. 1 is a block diagram illustrating the principle of the image signal reproduction process of the AM-PM-VSB modulation method. FIG. 2 is a waveform diagram of each part of FIG. 1. FIG. 3 is a waveform diagram showing how an image signal is reproduced from an AM-PM-VSB modulated signal in which jitter has partially occurred. Fourth
The figure is a block diagram showing a carrier wave recovery circuit showing one embodiment of the present invention. FIG. 5 is a waveform diagram of each part of FIG. 4. In the figures, the same reference numerals indicate the same or equivalent parts, 1 is a received signal input port, 2 is a carrier wave recovery circuit, 3 is a multiplier, 4 is a reduced pass filter,
5 is a signal restorer, 6 is a reproduced image signal output port, 2
1 is a band pass filter, 22 is a first pulse generator, 23 is a phase comparator, 24 is an integrator, 25 is a sawtooth wave oscillator, 26 is a second pulse generator, 27
28 is a subtracter, 29 is a comparator, and 30 is a frequency divider.

Claims (1)

[Claims] 1. Pulse generating means for generating a pulse at the intersection of the received signal subjected to carrier suppression modulation and the ground potential;
oscillation means that is voltage controllable and that oscillates a signal with a frequency N times the carrier wave (N is a positive integer); means that compares the phase of the oscillated signal and the pulse based on the pulse; and an output of the phase comparison means. means for applying a control voltage to the signal oscillation means in accordance with the signal oscillation means, further comprising means for generating a second pulse at a crossing point of the received signal with a ground potential, the second pulse and the oscillation signal, phase error detection means for detecting a phase error based on the oscillation signal, means for phase modulating the signal oscillated from the oscillation means by the output of the phase error detection means, and 1/N modulating the phase modulation output. Equipped with a means to divide the frequency into
A carrier wave recovery circuit, characterized in that the phase of the carrier wave corresponding to the portion where jitter occurs in the received signal is derived from the frequency dividing means as a recovered carrier wave whose phase is shifted by the amount of jitter.