JP4195856B2 - Signal transmission system - Google Patents

Description

  The present invention relates to a signal transmission system for transmitting a digital signal used in an interface or the like for connecting a computer and peripheral devices via an analog transmission line.

  Conventionally, in order to transmit a digital signal using an analog transmission line such as a telephone line, the digital signal is modulated and converted into an analog signal, then transmitted to the analog transmission line, and received on the receiving side from the analog transmission line. This was dealt with by demodulating an analog signal and returning it to a digital signal. Here, when demodulating an analog signal and returning it to a digital signal, a comparator and an ATC (Auto Threshold Control) circuit are often used.

  However, such a conventional modulation / demodulation method cannot be used for a signal having an extreme duty ratio. That is, when a signal that continues for a long period of time at a low level or a high level is transmitted to a narrow-band transmission line, a large waveform distortion occurs in the transmission line, and the original digital signal cannot be accurately determined. In addition, when a digital signal such as that used in the RS-232C interface that connects a computer and peripheral devices is modulated and transmitted via an analog transmission path in the voice band, the transmission path may depend on the modulation method. There is also a problem that the transmission efficiency of the digital signal is suppressed without fully utilizing the above bandwidth.

Problems in the conventional modulation / demodulation method will be described in detail below.
For example, when a digital signal used in the RS-232C interface is transmitted through an analog transmission line with a voice band of about 10 kHz, it is necessary to perform digital modulation. In order to perform this digital modulation, Since a certain amount of bandwidth is used, the actual transmission rate is limited.

  Also, since the audio signal is composed of a sine wave, the change is gentle and abrupt change is unlikely to occur, but the change of the digital signal is steep. Therefore, in order to transmit a digital signal via an analog transmission line in the voice band, it is necessary to perform signal processing that brings the waveform of the digital signal close to the waveform of the analog signal. Further, in order to restore the signal subjected to such signal processing to the original digital signal, a comparator for determining the signal level using the threshold value and an ATC circuit for controlling the threshold value are required. . However, when “0” or “1” continues, the range that can be handled by the ATC circuit is exceeded, and as a result, a state in which the pulse width per bit does not become constant in the restored digital signal occurs. To do.

  FIG. 7 is a diagram showing waveform changes in the conventional modulation / demodulation method. FIG. 7A shows the waveform of the original digital signal, FIG. 7B shows the waveform modulated into an analog signal, and FIG. 7C shows the demodulated signal. The waveform of a digital signal is shown. In addition, the broken line in FIG.7 (b) represents the threshold value in determination of a signal level.

  As shown in FIG. 7 (a), when “0” continues and the duty ratio becomes about 8%, when modulated to an analog signal, a waveform as shown in FIG. 7 (b) is obtained. Is demodulated into a digital signal, a waveform as shown in FIG. In the demodulated digital signal, deterioration in which the pulse width expands and contracts occurs, and the data ratio becomes abnormal as the duty ratio increases as compared with the original digital signal. In order to avoid such a data abnormality, the duty ratio that can be actually used is limited to a range of about 25% to 75%, and it is difficult to transmit data having a duty ratio outside the range.

By the way, the following Patent Document 1 discloses recording data output from a computer on an audio cassette tape by using a modem device (modem) that connects a data processing device and an analog telephone line. However, Patent Document 1 does not teach any novel modulation / demodulation method.
JP-A-57-89359 (page 1-2, FIG. 3)

  In view of the above, the present invention provides a signal transmission system capable of efficiently transmitting various digital signals used in an interface or the like for connecting a computer and peripheral devices via an analog transmission line. For the purpose.

In order to solve the above problems, a signal transmission system according to the present invention converts a level of an input digital signal having a predetermined bit rate to generate an NRZ signal, and outputs the NRZ signal to a predetermined level. A sampling unit that generates a synchronization signal by sampling at a frequency corresponding to or higher than the bit rate , and a timing signal based on a rising edge and / or a falling edge of the synchronization signal A timing generator for generating a bi-phase signal by synthesizing the synchronization signal and the timing signal and performing bi-phase modulation, and generating a clock pulse signal based on the timing signal A clock pulse generator, the bi-phase signal and the clock pulse signal Limit the transmission system circuit having the first and second analog circuits to be transmitted to the two analog transmission lines, and the levels of the two system signals respectively received from the two analog transmission lines. A receiving circuit that generates a biphase signal and a clock signal, restores the NRZ signal based on the biphase signal and the clock signal, shapes the waveform of the restored NRZ signal, converts the signal level, and outputs the signal It comprises.

  According to the present invention, based on an input digital signal, a biphase signal having a duty ratio within a certain range and a clock signal synchronized with the biphase signal are generated, and these signals are band-limited. Therefore, various digital signals used in an interface for connecting a computer and peripheral devices can be efficiently transmitted via the analog transmission path.

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, the same reference number is attached | subjected to the same component and description is abbreviate | omitted.
FIG. 1 is a block diagram showing a configuration of a transmission system circuit included in a signal transmission system according to an embodiment of the present invention. As shown in FIG. 1, a transmission system circuit inputs a signal (hereinafter referred to as “RS-232C signal”) used in an RS-232C interface for connecting a computer and peripheral devices with a serial cable. The modulation circuit 10 that modulates the −232C signal and outputs a biphase signal and a clock signal, and the biphase signal and the clock signal output from the modulation circuit 10 are band-limited and supplied to the two transmission lines 1 and 2. The analog circuit 16 and 17 are comprised.

The modulation circuit 10 includes a signal level conversion unit 11, a sampling unit 12, a timing generation unit 13, a biphase modulation unit 14, and a clock pulse generation unit 15.
The signal level conversion unit 11 inputs an RS-232C signal having a bit rate of 9600 bps (bit per second), converts the level of the RS-232C signal, and NRZ (non-return to Zero) signal is output.

The sampling unit 12 samples the NRZ signal output from the signal level conversion unit 11 at a frequency corresponding to a transmission bit rate of 9600 bps or a frequency higher than a frequency corresponding to the transmission bit rate , so that transmission is performed. Synchronize at the same time. The timing generation unit 13 generates a timing signal based on the rising edge and / or the falling edge of the synchronization signal Sa output from the sampling unit 12.

  The biphase modulation unit 14 generates the biphase modulation signal Sb by synthesizing the synchronization signal Sa output from the sampling unit 12 and the timing signal output from the timing generation unit 13 and performing biphase modulation. To do. The clock pulse generator 15 generates a clock pulse signal Sc based on the timing signal output from the timing generator 13.

  By performing biphase modulation in this way, the duty ratio of the biphase modulation signal Sb is limited to a range of 33.3% to 66.7%, and transmission is performed using an analog transmission line in the voice band. It is a suitable value. In addition, the duty ratio of the clock pulse signal Sc is set to approximately 50%.

  The analog circuit 16 includes an integrating circuit (low-pass filter), band-limits the bi-phase modulation signal Sb output from the bi-phase modulation unit 14 to generate an analog transmission signal Sb ′, and transmits this to the transmission line. 1 is supplied. Similarly, the analog circuit 17 also includes an integration circuit (low-pass filter), which limits the clock pulse signal Sc output from the clock pulse generator 15 to generate an analog transmission signal Sc ′. Supply to transmission line 2.

  As a result, the analog transmission signal Sb ′ obtained based on the biphase modulation signal Sb mainly has frequency components of 4800 Hz and 9600 Hz. The analog transmission signal Sc ′ obtained based on the clock pulse signal Sc mainly has a frequency component of 9600 Hz. Therefore, these analog transmission signals Sc and Sc 'can be transmitted through an analog transmission line having a voice band of about 10 kHz.

  FIG. 2 is a block diagram showing a configuration of a reception system circuit included in the signal transmission system according to the embodiment of the present invention. As shown in FIG. 2, the receiving circuit receives and demodulates the analog transmission signals Sb ′ and Sc ′ transmitted through the two transmission lines 1 and 2, respectively, and outputs an RS-232C signal. The circuit 20 is configured.

The demodulation circuit 20 includes signal level conversion units 21 and 22, a synthesis unit 23, a waveform shaping timing generation unit 24, a waveform shaping unit 25, and a signal level conversion unit 26.
In the present embodiment, each of the signal level conversion units 21 and 22 compares the analog transmission signal with a threshold value to binarize, and an ATC (controlling the threshold value used in this comparator). Auto threshold control) circuit.

  The signal level conversion unit 21 determines the level of the analog transmission signal Sb ′ transmitted via the transmission path 1 and converts it to a TTL level biphase modulation signal Sb with a bit rate of 9600 bps. The signal level conversion unit 22 determines the level of the analog transmission signal Sc ′ transmitted through the transmission path 2 and converts the analog transmission signal Sc ′ into a TTL level clock pulse signal Sc.

  In the present embodiment, the synthesizer 23 is configured by an exclusive OR circuit that obtains an exclusive OR of the biphase modulation signal Sb and the clock pulse signal Sc. The synthesizer 23 obtains an exclusive OR, and synthesizes the biphase modulation signal Sb and the clock pulse signal Sc to generate a synthesized signal Sd.

  The waveform shaping timing generator 24 shapes the waveform of the clock pulse signal Sc to generate a waveform shaping timing signal Se. The waveform shaping unit 25 generates a correction signal Sf by correcting a glitch (spike-like noise) of the synthesized signal Sd using the waveform shaping timing signal Se. The signal level conversion unit 26 converts the level of the TTL level correction signal Sf and outputs the converted signal as an RS-232C signal.

  FIG. 3 is a waveform diagram showing signal waveforms in respective parts of the transmission system circuit shown in FIG. 1 and the reception system circuit shown in FIG. In the transmission circuit, by performing biphase modulation based on the synchronization signal Sa output from the sampling unit 12, the phase is inverted when the synchronization signal Sa is “0” and “1”. A biphase modulation signal Sb is generated. A timing signal is generated based on the rising edge and / or the falling edge of the synchronization signal Sa, and the clock pulse signal Sc is generated based on the timing signal.

  On the other hand, in the reception system circuit, a composite signal Sd is generated by obtaining an exclusive OR of the biphase modulation signal Sb and the clock pulse signal Sc. That is, when the biphase modulation signal Sb and the clock pulse signal Sc are a combination of “0” and “1”, the combined signal Sd becomes “1”, and both the biphase modulation signal Sb and the clock pulse signal Sc are “ The composite signal Sd becomes “0” when “0” or both are “1”. However, when the biphase modulation signal Sb or the clock pulse signal Sc changes, a glitch is generated in the synthesized signal Sd. Therefore, the glitch of the synthesized signal Sd is obtained using the waveform shaping timing signal Se obtained from the clock pulse signal Sc. Is removed, and a correction signal Sf is generated.

  FIG. 4 is a diagram showing a waveform change of a signal having a duty ratio of 50% in the signal transmission system according to the present invention. 4A shows the waveform of the original digital signal, FIG. 4B shows the waveform modulated into an analog signal, and FIG. 4C shows the demodulated signal. The waveform of a digital signal is shown. In addition, the broken line in FIG.4 (b) represents the threshold value in level determination.

  As shown in FIG. 4A, when the duty ratio is 50%, even if the signal is modulated into an analog signal and demodulated after the waveform shown in FIG. As shown in FIG.

  FIG. 5 is a diagram showing a waveform change of a signal having a duty ratio of 33.3% in the signal transmission system according to the present invention. FIG. 5A shows the waveform of the original digital signal, FIG. 5B shows the waveform modulated into an analog signal, and FIG. 5C shows the demodulated signal. The waveform of a digital signal is shown. In addition, the broken line in FIG.5 (b) represents the threshold value in level determination.

  When the duty ratio is 33.3% as shown in (a) of FIG. 5, the waveform shown in (b) of FIG. 5 is obtained when modulated to an analog signal, and when this is demodulated into a digital signal, the waveform of FIG. The waveform is as shown in (c). In the demodulated digital signal, although the duty ratio is slightly increased as compared with the original digital signal, the expansion and contraction of the pulse width is suppressed by the operation of the ATC circuit, and the data can be processed.

  FIG. 6 is a diagram showing a waveform change of a signal having a duty ratio of 66.7% in the signal transmission system according to the present invention. 6A shows the waveform of the original digital signal, FIG. 6B shows the waveform modulated into an analog signal, and FIG. 6C shows the demodulated signal. The waveform of a digital signal is shown. In addition, the broken line in FIG.6 (b) represents the threshold value in level determination.

  When the duty ratio is 66.7% as shown in FIG. 6 (a), a waveform as shown in FIG. 6 (b) is obtained when modulated to an analog signal. The waveform is as shown in (c). In the demodulated digital signal, although the duty ratio is slightly reduced as compared with the original digital signal, the expansion and contraction of the pulse width is suppressed by the operation of the ATC circuit, and the data can be processed.

  The present invention can be used in a signal transmission system for transmitting a digital signal used in an interface or the like for connecting a computer and peripheral devices via an analog transmission line.

It is a block diagram which shows the structure of the transmission system circuit contained in the signal transmission system which concerns on one Embodiment of this invention. It is a block diagram which shows the structure of the receiving system circuit contained in the signal transmission system which concerns on one Embodiment of this invention. FIG. 3 is a waveform diagram showing signal waveforms in respective parts of the transmission system circuit shown in FIG. 1 and the reception system circuit shown in FIG. 2. It is a figure which shows the waveform change of the signal whose duty ratio is 50% in the signal transmission system which concerns on this invention. It is a figure which shows the waveform change of the signal whose duty ratio is 33.3% in the signal transmission system which concerns on this invention. It is a figure which shows the waveform change of the signal whose duty ratio is 66.7% in the signal transmission system which concerns on this invention. It is a figure which shows the waveform change in the conventional modulation / demodulation system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 Transmission path 10 Modulation circuit 11 Signal level conversion part 12 Sampling part 13 Timing generation part 14 Biphase modulation part 15 Clock pulse generation part 16, 17 Analog circuit 20 Demodulation circuit 21, 22 Signal level conversion part 23 Synthesis part 24 Waveform shaping timing generation unit 25 Waveform shaping unit 26 Signal level conversion unit

Claims (3)

A signal level conversion unit that converts the level of an input digital signal having a predetermined bit rate to generate an NRZ signal , and samples the NRZ signal at a frequency corresponding to the predetermined bit rate or higher than the frequency A sampling unit that generates a synchronization signal, a timing generation unit that generates a timing signal based on a rising edge and / or a falling edge of the synchronization signal, and the synchronization signal and the timing signal are combined A bi-phase modulation unit that generates a bi-phase signal by performing bi-phase modulation, a clock pulse generation unit that generates a clock pulse signal based on the timing signal, and a band of the bi-phase signal and the clock pulse signal. 1st and 2nd to transmit to 2 analog transmission lines A transmission circuit having an analog circuit of
The bi-phase signal and the clock signal are generated by determining the levels of the two systems of signals received from the two analog transmission lines, and the NRZ signal is restored and restored based on the bi-phase signal and the clock signal. A receiving circuit that shapes the waveform of the NRZ signal and converts and outputs the signal level;
A signal transmission system comprising:   A second and third signal level conversion unit for generating a biphase signal and a clock pulse signal by determining the levels of the two systems of signals received from the two systems of analog transmission lines, respectively, A synthesis unit that generates a synthesized signal by synthesizing the biphase signal and the clock pulse signal; a waveform shaping timing generation unit that generates a waveform shaping timing signal by shaping a waveform of the clock pulse signal; and the waveform shaping A waveform shaping unit that generates a correction signal by correcting the synthesized signal using a timing signal; and a fourth signal level conversion unit that restores a digital signal by converting the level of the correction signal. Item 1. The signal transmission system according to Item 1.   The signal transmission system according to claim 2, wherein the synthesis unit generates the synthesized signal by obtaining an exclusive OR of the biphase signal and the clock pulse signal.

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