JP2005295086A - Data transmission circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a data transmission circuit capable of suppressing distortion of waveform due to magnification current and occurrence of transmission error by suppressing a counter electromotive voltage generated when a driver is turned off without decreasing the value of a termination resistance. <P>SOLUTION: The data transmission circuit comprises a waveform distortion measuring circuit 17 comprising an up/down counter 19 for measuring the width of the "H" pulse and "L" pulse of an output pulse during transmission of actual data, and a transmission data control circuit 18 transmitting extra data for suppressing a counter electromotive voltage generated in a pulse transformer 15 based on pulse distortion measured in the waveform distortion measuring circuit 17 after transmission of actual data. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a data transmission circuit that improves noise resistance and prevents transmission errors in a two-wire data transmission system that uses a pulse transformer and is electrically insulated from a transmission line.

The data transmission circuit of the prior art has adopted a balanced transmission system using a differential output type driver, a differential input type receiver, and a balanced circuit as a technique for improving noise resistance and preventing transmission errors ( For example, see Patent Document 1).
FIG. 4 is a block diagram showing a conventional data transmission circuit.
In FIG. 4, 1 is a data transmission circuit for transmitting and receiving data, 11 is a communication control IC, 12 is a differential bus transceiver (hereinafter referred to as a transceiver), 13 is a driver, 14 is a receiver, and 15 is a pulse transformer. , 16 is a terminating resistor, 20 is a communication cable, en is a transmission enable signal, and td is a pair of differential signals (hereinafter referred to as transmission data) output from the transceiver 12.
The transceiver 12 serving as a transmission / reception interface unit includes a driver 13 and a receiver 14. Output of transmission data, input of reception data, and output of a transmission enable signal en for controlling the transceiver 12 are performed by the communication control IC 11.
The communication cable 20 connects between the data transmission circuit 1 and at least one or more similar data transmission circuits, and the data transmission circuits at both ends of the communication cable 20 are adapted to match the characteristic impedance of a pair of wires. Terminal resistor 16 is provided. The communication cable 20 and the data transmission circuit 1 are electrically insulated by a pulse transformer 15.
FIG. 5 is a timing chart showing the transmission data frame configuration of the prior art.
In FIG. 5, 31 is a first station transmission data frame, 32 is a second station transmission data frame, and 33 is an nth station transmission data frame (n is the number of connected stations).
When transmission is performed using the data transmission circuit shown in FIG. 4, data transmission is performed in a frame configuration as shown in FIG.
Since the data transmission circuit 1 is in a reception waiting state after the data transmission of its own station is completed until another station transmits data, there is a pause period between the data frames of each station. Since no station drives the transmission line during this idle period, the transmission line is in a floating state.
FIG. 6 is an explanatory diagram showing a waveform obtained by enlarging one bit of transmission data of the prior art.
A coding system that performs level inversion at the midpoint of transmission data bits (hereinafter referred to as the Manchester coding system) is used. In the Manchester encoding method, data is “0” when the first half of the data is “L” level and the second half is “H” level, and “1” when the first half is “H” level and the second half is “L” level. Therefore, since the level inversion always occurs at the midpoint of the bit, ideally, the pulse widths of the “H” level and “L” level are equal as shown in the waveform of FIG. In the transmission line, an “H” level is a positive polarity and an “L” level is a negative polarity AC signal, and no DC component is generated in the transmission signal.
In this way, in the conventional data transmission circuit, the transmission control signal 11 is set to “H” during transmission of the data of the own station by the communication control IC 11 and the driver 13 in the transceiver 12 is enabled to perform data transmission, and the data transmission is completed. Then, the transmission enable signal en is set to “L”, the driver 13 is disabled, and the reception of data from another station is awaited.
Japanese Patent Laid-Open No. 06-85796 (see FIG. 10)

However, in the conventional data transmission circuit, since the communication control IC 11 and the transceiver 12 have skew characteristics, the output data is biased to “H” or “L”, and the output pulse width is distorted.
FIG. 7 is an explanatory diagram showing a case where the data waveform for 1 bit is biased to “H” by Δt.
7A shows a waveform when the data waveform for one bit is biased to “H” by Δt, FIG. 7B shows a pulse waveform equivalent to the waveform shown in FIG. 7A, and FIG. 7C shows distortion in the transmission data. It is a magnetizing current waveform generated in a pulse transformer in a certain case.
The pulse when the data waveform for 1 bit is biased to “H” by Δt has the waveform shown in FIG. This indicates the same thing as the generation of the pulse shown in FIG. In order to improve noise resistance, the transmission circuit 1 and the communication cable 20 are insulated from each other by the pulse transformer 15. However, when the pulse shown in FIG. A magnetizing current as shown by a solid line in (c) flows. This magnetizing current is consumed and attenuated by the terminating resistor 16 or the like when no pulse is input. However, when data bits are output continuously, the next data bit is output before the magnetizing current for 1 bit of data is consumed and becomes 0, so that the one-dot difference line in FIG. Magnetization current is accumulated in the pulse transformer 15. When the transmission circuit 1 completes the output of data and turns off the driver 13, no station is driven in the transmission path, and the pulse transformer 15 generates a back electromotive voltage in an attempt to continue the accumulated magnetizing current. The counter electromotive voltage is attenuated during a pause period between frames of transmission data and finally becomes 0. However, when the accumulated magnetizing current is large, the magnetizing current is attenuated and becomes 0. Then, the frame of the next station started, and there was a problem that the waveform was distorted or a transmission error occurred due to this magnetizing current.
It is conceivable to reduce the value of the termination resistor 16 in order to quickly attenuate this magnetizing current to zero during the pause period between frames, but the resistance value is reduced and the transmission line and impedance are adapted. In addition, it is necessary to add inductance separately, and there is a problem that the current consumption increases because the resistance value becomes small.
The present invention has been made in view of such problems, and suppresses the back electromotive voltage generated when the driver is turned off without reducing the value of the termination resistor, thereby generating waveform distortion and transmission error due to the magnetizing current. An object of the present invention is to provide a data transmission circuit capable of suppressing the above.

  In order to solve the above problems, a data transmission circuit of the present invention includes a pulse transformer connected on a transmission line and electrically insulated from the transmission line, and a driver for transmitting a transmission signal on the transmission line. And a data transmission circuit comprising a receiver for detecting a transmission signal transmitted on the transmission line and a communication control IC for controlling transmission / reception data, wherein the data transmission circuit measures a waveform distortion amount of the transmission signal. A waveform distortion measuring circuit for controlling transmission data and a transmission data control circuit for controlling transmission data, the waveform distortion measuring circuit comprising an up / down counter for measuring a pulse width, Pulse distortion by measuring the width of “H” pulse and “L” pulse of the output pulse of the receiver during actual data transmission that is data to be transmitted to the station The transmission data control circuit is configured to acquire a measurement value and transmit additional data for suppressing a counter electromotive voltage generated in the pulse transformer based on the pulse distortion measurement value after completion of the actual data transmission. It is characterized by that.

  According to the data transmission circuit of the present invention, the output pulse distortion during actual data transmission is measured, and the additional data for canceling the accumulated magnetizing current based on the distortion measured after the actual data transmission is output. As a result, the back electromotive voltage generated in the pause period between frames can be suppressed without reducing the value of the termination resistance, and the occurrence of waveform distortion and transmission error due to the magnetizing current can be suppressed.

  Hereinafter, specific examples of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a data transmission circuit of the present invention.
In FIG. 1, 17 is a waveform distortion measurement circuit for measuring the amount of waveform distortion of transmission data, 18 is a transmission data control circuit for controlling transmission data, and cnt is a waveform distortion measurement for controlling the waveform distortion measurement circuit 17. The circuit control signal, dis, is a waveform distortion measurement value indicating the waveform distortion measurement result. Note that the same reference numerals as those in FIG. 4 are the same components and indicate the same functions, and thus the description thereof is omitted.
FIG. 2 is a block diagram showing details of the waveform distortion measuring circuit 17 of the present invention.
In FIG. 2, 19 is an up / down counter. Note that the same reference numerals as those in FIG. 1 indicate the same components and the same functions, and thus description thereof is omitted.
The features of the present invention are as follows.
That is, the data transmission circuit 1 includes a waveform distortion measurement circuit 17 for measuring a waveform distortion amount of the transmission signal and a transmission data control circuit 18 for controlling transmission data, and the waveform distortion measurement circuit. Reference numeral 17 is an up / down counter 19 for measuring the pulse width. During transmission of actual data, which is data transmitted by the driver 13 to another station, an "H" pulse of an output pulse of the receiver 14, and an "L""The pulse distortion measurement value dis is obtained by measuring the width of the pulse, and the transmission data control circuit 18 suppresses the back electromotive voltage generated in the pulse transformer 15 based on the pulse distortion measurement value dis. The additional data to be transmitted is transmitted after the end of the actual data transmission.
Specifically, the present invention includes a waveform distortion measurement circuit 17 that takes in received data and a waveform distortion measurement circuit control signal cnt and sends a waveform distortion measurement value dis to the transmission data control circuit 18 in FIG. It becomes the composition.
FIG. 3 is a timing chart showing the operation of the data transmission circuit of the present invention.
A timing chart of a transmission enable signal en, transmission data, transmission data td (differential signal), reception data, waveform distortion measurement circuit control signal cnt, waveform distortion measurement value dis, and clock signal is shown.

The function of the data transmission circuit of this embodiment will be described below with reference to FIGS.
The transmission data control circuit 18 in the communication control IC 11 starts transmission data by setting the transmission enable signal en to “H” when the transmission frame of the local station is reached, and simultaneously sets the waveform distortion measurement circuit control signal cnt to “H”. The operation of the up / down counter 19 of the waveform distortion measuring circuit 17 is started. Transmission data output from the transmission data control circuit 18 is input to the up / down counter 19 as reception data via the driver 13 and the receiver 14. The up / down counter 19 counts up when the received data is “H” when the clock signal is input (part (B) in FIG. 3), and counts down when the received data is “L” (FIG. 3). (Part (A)). When there is no distortion in the transmission data, the value of the up / down counter 19 becomes 0 when the transmission of one bit of data is completed. However, when the transmission data is distorted, the count value is set when the transmission of data of one bit is completed. It is biased to either positive or negative instead of zero. The timing chart shown in FIG. 3 shows a case where the transmission data is distorted to “H”.
The up / down counter 19 accumulates waveform distortion for each bit of transmission data, and measures the amount of waveform distortion in the entire actual data. When the transmission data control circuit 18 completes the transmission of the actual data, the waveform distortion measurement circuit control signal cnt is set to “L” to stop the waveform distortion measurement, and the waveform distortion measurement value dis output from the up / down counter 19 at that time is stopped. Thus, additional data for canceling the counter electromotive voltage generated in the pulse transformer 15 is transmitted. That is, in the timing chart of FIG. 3, since the transmission data is distorted to “H” and a back electromotive voltage of “L” is generated after data transmission is completed, the transmission data control circuit 18 uses “L” data as additional data. By outputting only the waveform distortion measurement value dis, it is possible to suppress the back electromotive voltage.
When the transmission of the additional data is completed, the transmission enable signal en is set to “L”, the driver 13 is disabled, and the reception of data from another station is awaited.

  As described above, the data transmission circuit 1 according to the embodiment of the present invention measures the width of the “H” pulse and the “L” pulse of the output pulse during actual data transmission that is data to be transmitted to another station. To transmit additional data for suppressing the back electromotive voltage generated in the pulse transformer 15 based on the waveform distortion measurement circuit 17 including the up / down counter 19 and the pulse distortion measured by the waveform distortion measurement circuit 17 after the actual data transmission is completed. Since the transmission data control circuit 18 is provided, the back electromotive voltage generated when the driver is turned off can be suppressed, and the occurrence of waveform distortion and transmission error due to the magnetizing current can be suppressed.

  By measuring the distortion of the output pulse width during data transmission and adding additional data that corrects the distortion of the entire transmission data, the back electromotive voltage generated by the pulse transformer after data transmission can be suppressed. The present invention can also be applied to data transmission using a balanced transmission circuit using a pulse transformer, a differential output type driver, a differential input type receiver, and a balanced circuit.

The block diagram which shows the data transmission circuit of this invention The block diagram which showed the detail of the waveform distortion measurement circuit 17 of this invention Timing chart showing operation of data transmission circuit of the present invention Block diagram showing a prior art data transmission circuit Timing chart showing prior art transmission data frame configuration Explanatory drawing which showed the waveform which expanded 1 bit of transmission data of the prior art (A) Waveform when 1-bit data waveform is biased to “H” by Δt (b) Waveform shown in (a) (C) Magnetization current waveform generated in the pulse transformer when transmission data is distorted

Explanation of symbols

1 Data transmission circuit 11 Communication control IC
DESCRIPTION OF SYMBOLS 12 Transceiver 13 Driver 14 Receiver 15 Pulse transformer 16 Termination resistance 17 Waveform distortion measurement circuit 18 Transmission data control circuit 19 Up / down counter 20 Communication cable 31, 32, 33 Transmission data frame en Transmission enable signal td Transmission data dis Waveform distortion measurement value cnt Waveform distortion measurement circuit control signal

Claims (1)

A pulse transformer (15) connected on the transmission line and electrically insulated from the transmission line, a driver (13) for transmitting a transmission signal on the transmission line, and transmitted on the transmission line In a data transmission circuit comprising a receiver (14) for detecting a transmission signal to be transmitted and a communication control IC for controlling transmission / reception data,
The data transmission circuit (1) includes a waveform distortion measurement circuit (17) for measuring the amount of waveform distortion of the transmission signal, and a transmission data control circuit (18) for controlling transmission data,
The waveform distortion measuring circuit (17) includes an up / down counter (19) for measuring the width of a pulse, and the receiver (14) during actual data transmission which is data transmitted from the driver (13) to another station. ) To obtain a pulse distortion measurement value (dis) by measuring the width of the “H” pulse and the “L” pulse of the output pulse of
The transmission data control circuit (18) transmits additional data for suppressing the back electromotive voltage generated in the pulse transformer (15) after the actual data transmission is completed based on the pulse distortion measurement value (dis). A data transmission circuit characterized by that.

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