JPH0553343B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a bus network transmission device, and more particularly to a transmission device for a node accessing a bus network.

[Conventional technology]

Figure 3 shows, for example, "Design of a sequel OP amplifier circuit"
Written by Hiroo Okamura CQ Publishing Co., Ltd. 5th edition Published in 1982 106
By configuring a differential line receiver using a comparator with the hysteresis characteristics described on the page, even if there is some noise signal at idle, the conventional method was designed not to output a significant signal to the LED driver. This is a bus type optical network transmitter. In the figure, 1 is a transformer, 2 and 3 are terminating resistors, 4 and 5 are resistors for signal separation between differential line receiver 6 and transformer 1, 7 is a differential line receiver positive phase input terminal, and 8 is a differential type Line receiver negative phase input terminal, 9 is differential line receiver positive phase output terminal, 10 is LED driver, 11
is an LED, 12 is an optical fiber for bus type network access, 13 is a positive feedback resistor, 14 is a reference voltage terminal, 15 is a resistor for signal separation between the power supply and the differential type line receiver input, 16 is a capacitor for power supply reset, 17 is the power terminal. Next, the operation will be explained below with reference to the operation waveform diagram of each part shown in FIG. 4. The input signal that passes through the transformer 1 and is terminated by the terminating resistors 2 and 3, that is, the differential mode input signal 1a with the pulse width allowed by the transformer coupling, is transmitted to the differential line receiver 6 and the signal separating resistor 4 between the transformer 1. ,5
are input to the positive phase input terminal 7 and the negative phase input terminal 8 of the differential line receiver 6 as a differential line receiver positive phase input signal 7a and a negative phase input signal 8a, respectively. The signal 9a output from the positive phase output terminal 9 of the differential line receiver 6 is input to the LED driver 10, which outputs a current corresponding to the input signal and transmits the optical signal from the LED 11 to the bus type network. Output to the work access optical fiber 12. The differential mode input signal 1a generated at both ends of the terminating resistors 2 and 3 described above may be of a code format with few consecutive codes of the same polarity (for example, a format such as a Manchester code in which each bit always has one sign change point). ) is used. This is because the differential mode input signal is input through transformer 1, and the DC component is short-circuited by transformer 1. Therefore, if the same polarity sign continues for a long time, the differential input amplitude becomes 0.
This is because the differential line receiver 6 may malfunction. Furthermore, in an idle state in which the transmitting device does not send out optical signals to the bus network, a differential mode input signal 1a is input so that the differential amplitude is 0 (V) so that no current flows through the transformer 1. Ru. This is because, in general, a bus type network transmitter needs to be designed with great care, since if it accidentally sends a signal to the bus type network when it is idle, it will interfere with the signals of other stations. The output 9a of the differential line receiver 6 mentioned above is positively fed back to the positive phase input terminal 7 via the positive feedback resistor 13. The reference voltage terminal supplies a voltage equal to the center level of the output 9a of the differential line receiver 6. Therefore, the positive phase input 7a of the differential line receiver 6 has an offset voltage due to positive feedback with respect to the negative phase input 8a, and during idle, the output 9a of the differential line receiver 6 maintains the transmission end state. do. Therefore, the input signal conditions stipulate that the final input signal ends with a change from "L" to "H". The differential line receiver output 9b when noise is mixed is connected to the differential line receiver positive phase input 7a when the power is turned on by a resistor 15 for signal separation between the power supply and the input of the differential line receiver and a capacitor 16 for resetting the power supply. momentarily power terminal 17
Since the voltage is increased to , the voltage is at the "H" level, which is the idle state. However, the differential mode input signal 1b mixed with noise provided via the power supply, transmission line, etc.
is input to the transmitting device, when the difference between the normal phase input 7b and the negative phase input 8b of the differential line receiver mixed with the noise exceeds the hysteresis width, the output 9b becomes a significant state "L" and The above state is maintained by hysteresis operation until the next transmission signal is input.

[Problems to be solved by the invention]

By the way, in the conventional bus-type network transmitter having the above-mentioned configuration, when the network is idle,
If noise exceeding the hysteresis width is input to the differential line receiver 6 for some reason, the output 9b of the differential line receiver 6 becomes the "L" level, which is a significant state, and the bus network Since optical signals must be continuously sent to other nodes, there are problems such as deterioration in the quality of signals sent from other nodes or the possibility of making communication across the entire bus network impossible. . This invention was made to solve the above problems, and even if the differential line receiver malfunctions due to noise exceeding the hysteresis width input to the differential line receiver, other It is an object of the present invention to provide a bus-type network transmitting device that does not degrade the quality of signals transmitted from nodes or make communication across the entire bus-type network impossible.

[Means to solve the problem]

The bus type network transmission device according to the present invention includes a peak detection circuit that outputs a signal responsive to the polarity of a negative phase output signal output from a differential line receiver, and a preset output signal level of the peak detection circuit. and a switching means that adjusts the input signal of the differential line receiver by performing a switching operation based on the signal output from the comparison means. It is.

[Effect]

The bus type network transmission device of the present invention detects a peak when the abnormal polarity of the negative phase output signal output from the differential line receiver continues for a pulse width longer than the pulse width of the input signal allowed by transformer coupling. When the output signal level of the circuit exceeds the reference level, the switching means is made conductive by the output signal from the comparison means and the differential line receiver input is reset, thereby preventing the differential line receiver from malfunctioning due to noise signals, etc. It is possible to automatically return to a normal state in an extremely short period of time.

【Example】

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram of a bus type network transmitting device according to an embodiment of the present invention, and reference numbers 1 to 17 are the same as those of the conventional device. In FIG. 1, 22 is a differential line receiver negative phase output terminal, and a peak detection resistor 23 and a capacitor 24 are connected in parallel to the differential line receiver negative phase output terminal 22. The peak detection circuit includes the peak detection resistor 23 and capacitor 24.
and a differential line receiver with negative phase output. It is assumed that the negative phase output section of the differential line receiver 6 described above is constituted by an open emitter type emitter follower circuit. The peak detection circuit charges a polarity output indicating non-transmission of the reverse phase output of the line receiver, and discharges a polarity output indicating transmission (abnormal polarity). A comparator 25 serving as a comparison means has its negative phase input terminal 26 connected to the peak detection circuit, and its positive phase input terminal 27 connected to a reference voltage setting circuit (not shown). The comparator 25
The output terminal 28 of is connected to the anode side terminal of a diode 29. The comparator 25 compares the output level of the peak detection circuit inputted from the negative phase input terminal 26 with a reference voltage inputted from the positive phase input terminal 27, that is, a threshold value serving as a reference level. Therefore, an output signal is outputted from the output terminal 28 to the anode side terminal of the diode 29. Next, the operation of the bus-type network transmitting apparatus having the above-mentioned structure will be described below with reference to the operational waveform diagram of each part shown in FIG. The peak detection resistor 23 and capacitor 2
4, the output signal level of the peak detection circuit changes. This output level is input to the negative phase input terminal 26 of the comparator 25 and compared with the threshold voltage 27a input from the positive phase input terminal 27 of the comparator 25. When the differential line receiver 6 is in a normal operating state, the output waveform 22a of the peak detection circuit that detects continuous output of abnormal polarity of the negative phase output signal of the differential line receiver 6 is at a threshold value. 2
7a, the logic level of the signal 28a output from the output terminal 28 of the comparator 25 is "L". The logic level “L” of the signal 28a output from the comparator 25 is set to have a lower potential than the voltage level “L” of the differential line receiver positive phase input 7a, and The logic level "H" of the output signal 28a is set to have a higher potential than the voltage level "H" of the differential line receiver positive phase input signal 7a. Therefore, when the differential line receiver 6 is in a normal operating state, the logic level of the signal 28a output from the comparator 25 is always at a lower potential than the differential line receiver positive phase input signal 7a. Therefore, the diode 29 is reverse biased and is in a non-conducting state. If the diode 29 is in a non-conductive state in this way, the positive-phase input signal 7a of the differential line receiver 6 is not affected by the output signal 28a from the comparator 25, so that the differential Due to the hysteresis operation of the differential line receiver 6, an "H" level signal can be obtained as the positive phase output signal 9a of the differential line receiver 6 during idle, and a significant signal corresponding to the data can be obtained during data transmission. However, if for some reason a differential mode input signal 1c mixed with noise is applied via a power supply or a transmission line, etc., and is input to the differential line receiver 6, unlike the conventional example, the following explanation will be made. It is possible to automatically recover from an abnormal state to a normal state through the following process. That is, when the differential mode input signal 1c is input to the differential line receiver 6, the differential line receiver output signal 9 mixed with noise from the line receiver 6 is generated.
Initially, c becomes a significant "L" level due to differential noise. When this state is maintained, the voltage level of the negative phase output signal 22c of the differential line receiver 6 becomes "H".
Therefore, the transistor constituting the negative phase output section of the differential line receiver 6 becomes non-conductive, and the difference is determined by the resistance value of the peak detection resistor 23 and the capacitance value of the capacitor 24. The output signal level 22c of the peak detection circuit of the negative phase output signal of the dynamic line receiver 6 rises (discharges) and finally rises above the threshold value 27a which is input to the comparator 25 via the positive phase input terminal 27. do. At this moment, the logic level of the output signal 28c from the comparator 25 becomes "H", and the diode 29 is forward biased, so that the diode becomes conductive. As a result, the potential of the positive phase input terminal 7 of the differential line receiver 6 increases, and the voltage level of the positive phase output signal 9c of the differential line receiver 6 becomes "H" again. Type line receiver 6
Reset. When the differential line receiver 6 is reset, the negative phase output signal of the differential line receiver 6 becomes "L" again, so the transistor constituting the negative phase output section of the differential line receiver 6 conducts and rapidly charges the capacitor 24,
Since the negative phase input signal of the comparator 25, that is, the output signal level 22c of the peak detection circuit is restored, the logic level of the signal 28c output from the comparator 25 becomes "L" and returns to the normal state. The time it takes to return to this normal state depends on the resistance value of the peak detection resistor 23 and the capacitor 24 described above.
Although it is determined by the capacitance value of , it is possible to set the time to a short time without causing any practical problems. Further, the reason for using the peak detection circuit is as follows. In other words, the differential line receiver 6
The output signal is a digital signal of H or L, and if this digital signal is inputted to the comparator 25 as it is, each time an H is output to the negative phase output terminal 22 of the differential line receiver 6, the comparator 25 outputs a reset signal and does not operate normally. Therefore, the peak detection circuit detects the negative phase output signal of the negative phase output terminal 22, and the threshold value of the comparator 25 is exceeded only when the negative phase output signal continues to be in the H state for more than the pulse width of the input signal. I have to. In this way, a peak detection circuit is required to detect an abnormality in the differential line receiver 6 based on the fact that its negative phase output signal continues to have an abnormal polarity for longer than the pulse width of the input signal. Moreover, according to the bus-type network transmission device having the above-described configuration, this device does not require a power source or a power source as in the conventional example.
Resistor 15 for signal separation between differential line receiver inputs
Since there is no need for a power supply reset circuit constituted by the power supply reset capacitor 16, it is possible to prevent noise from entering through the power supply reset circuit, and it is possible to greatly reduce the frequency of occurrence of malfunctions. In the above embodiment, the output terminal 2 of the comparator 25
8 and the positive phase input terminal 7 of the differential line receiver 6 is shown, but depending on the output level from the comparator 25,
A similar effect can be obtained by connecting a level shift diode and a resistor in series between the output terminal 28 and the positive phase input terminal 7. In addition, as the above embodiment, a bus-type network transmission device using optical fibers has been described;
Of course, similar effects can also be obtained in a bus type network transmitter using a coaxial cable driver instead of the LED driver 10.

【Effect of the invention】

As described above, according to the present invention, an input signal with a pulse width that is allowable for transformer coupling is input through the transformer coupling circuit, and the differential amplitude between the positive phase component and the negative phase component of this input signal is output. Due to positive feedback, even if a differential line receiver with hysteresis characteristics malfunctions, it can automatically return to a normal state in a very short time, resulting in a highly reliable bus-type network transmitter. be.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram of a bus-type network transmitter according to an embodiment of the present invention, FIG. 2 is an operational waveform diagram of each part constituting the bus-type network transmitter according to an embodiment of the present invention, and FIG. This figure is a circuit diagram of a conventional bus-type network transmitter, and FIG. 4 is an operational waveform diagram of each part constituting the conventional bus-type network transmitter. In the figure, 1 is a transformer, 6 is a differential line receiver, 10 is an LED driver, 13 is a positive feedback resistor, 23 is a peak detection resistor, 24 is a peak detection capacitor, 25 is a comparator, and 29 is a diode. be. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1 A differential signal with hysteresis characteristics due to positive feedback that inputs an input signal with a pulse width that is allowable for transformer coupling through a transformer coupling circuit and outputs the differential amplitude between the positive and negative phase components of this input signal. A bus-type network transmitter equipped with a differential-type line receiver includes a peak detection circuit that outputs a signal responsive to the polarity of a negative-phase output signal output from the differential-type line receiver, and an output signal level of the peak detection circuit. and a preset reference level, and the output signal has a larger amplitude than the input signal of the differential line receiver, and the switching operation is performed by the output signal from the comparison means. switching means for adjusting the input signal, when the output signal level of the peak detection circuit exceeds the reference level due to the abnormal polarity of the negative phase output lasting longer than the pulse width of the input signal, the switching means adjusts the input signal; A bus type network transmitting device characterized in that the output signal from the comparing means makes the switching means conductive to reset the differential line receiver.