JPS5915551B2 - Facsimile signal sampling method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sampling method for sampled facsimile signals that is asynchronous with the clock frequency of a transmission line.

Conventionally, when sampling a signal that is asynchronous with the sampling frequency of a transmission line, sampling methods called multi-point sampling method and dual mode method are known as methods for reducing distortion caused by this sampling.

However, this multi-point sampling method requires several times the number of code bits as in the case of synchronous relationship, and the dual mode method has the disadvantage that the number of additional bits for mode designation increases. In order to eliminate the drawbacks of the conventional example described above, the present invention inserts or removes stuff pulses provided in a period corresponding to the synchronization signal section of the facsimile signal, and effectively utilizes the characteristics of the facsimile signal. The present invention provides a facsimile signal sampling method that enables synchronous sampling.

Hereinafter, embodiments will be described in detail with reference to the drawings. Figure 1 shows
FIG. 1A shows a signal conversion process for explaining the sampling method of the present invention.
Figures B and B' are transmission signals. A facsimile signal is composed of an image signal section PIX and a phase signal section PHS. Let the number of pulses in one frame be N, and the clock accuracy be E. If this signal is synchronously sampled with the clock of the transmission line, 1
The time difference after the frame is in units of sampling interval,
Only N6, = N-E (bits) is generated.

If 1N, 1≦0.5, sample the next frame in the same way, and if 1N, 1>0.5, insert (N,) pulses into the phase signal interval PHS. Alternatively, by erasing, the starting point of the next frame can be kept within 0.5 bits. This pulse is similar in concept to the normal staff pulse used in the multiplex synchronization system of PCM communication, and the number required per frame can be considered to be approximately {NJ+1. That is, N
=2000bit. If E-10-4 is used, synchronous sampling becomes possible by increasing or decreasing the pulse of 1 bit in one frame. FIG. 2 shows an embodiment of the present invention, where 1 is an input terminal for a facsimile signal, 2 is a first-in-first-out shift register that creates a matrix, 3 is a shift register, and 4 is an output terminal. terminal, 5
6 is a synchronous signal detection circuit, 6 is a counter for addition and subtraction, 7 is a gate circuit for inserting and inhibiting pulses, and 8 is a transmission line clock input terminal.

Next, to explain the operation of this embodiment, first, the signal inputted from 1 is inputted to the shift register 2 using its own clock, outputted using the clock from the gate circuit 7, and sent to the transmission line clock from the input terminal 8. Therefore, it is input to the shift register 3 and output to the output terminal 4 after a certain delay.

Further, when a synchronization signal is identified by the detection circuit 5 from the contents of the shift register 3, the gate circuit 7 is driven by the contents of the counter 6, and the pulses supplied to the shift register 2 are controlled. The counter 6 subtracts the number of pulses of the facsimile signal from the input terminal 1 and the number of pulses of the transmission line clock from the input terminal 8, and stores the difference between the two within one frame. That is, if the clock on the transmission line is N1 bits less, the gate circuit 7 sends out a pulse of N1 bits to decrease the contents of the shift register 2 by N1 bits. Also, if the transmission line clock has N2 bits,
The gate circuit 7 inhibits the N2 bits and inputs the extra N2 bits to the shift register 3. In order to prevent the image signal from being erroneously caused by this operation, a bit group consisting of {Nε}+1 "0" and one "1" may be provided at the rear of the synchronizing signal, for example.

FIG. 3 illustrates this situation. FIG. 3A shows a reference facsimile signal, FIG. 3B shows a case where a bit is inserted, and FIG. 3C shows a case where a bit is deleted.
In order to restore the transmission line signal to the original facsimile signal, it is sufficient to detect the last 1 of the changed bit group and make the next bit correspond to the beginning of the frame.

In addition, on the receiving side, by knowing the number of stuff pulses, the number of clock pulses of the terminal before being sampled on the transmission path can be detected, and a phase smoothing circuit configured with a phase control loop can be used to control the clock pulses of the transmitting terminal. It is clear from the example of the staff synchronization technique used in the PCM multiplex synchronization system that it is possible to reproduce and restore the original signal sequence. As explained above, according to the present invention, synchronous sampling can be performed by synchronizing the asynchronous facsimile signal using the synchronization period, which is effective when resampling the facsimile signal. Therefore, the present invention can provide a very useful sampling method for facsimile signals.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating signal conversion of the method of the present invention,
FIG. 2 is a block diagram of an embodiment of the present invention, and FIG. 3 is a diagram illustrating signal conversion according to the present invention. 1... Input terminal, 2... First-in/7 first-out shift register, 3...
・Shift register, 4... Output terminal, 5...
... Synchronous signal detection circuit, 6 ... Counter, 7
......Gate circuit, 8...--Transmission line clock input terminal.

Claims (1)

[Claims] 1. In a method in which a facsimile signal sampled by the clock of a facsimile terminal, which is asynchronous with the sampling clock frequency of the transmission line, is sampled again on the transmission line, the frequency of the sampling clock of the facsimile signal and the sampling clock of the transmission line is Sampling of a facsimile signal, characterized in that synchronous sampling is performed by detecting a speed difference and inserting or erasing a stuff pulse provided in a period corresponding to a synchronization signal section of the facsimile signal according to the detection. method.