Telecommunications Equipment

Abstract

To provide a communication device capable of easily suppressing a reflected signal with a simple circuit configuration and capable of suppressing the reflected signal without requiring a circuit change even if the length of an electric wire is changed. [Solution] In a push-pull driven transmission circuit 2 of a communication device 1, a reflected signal suppression circuit 10 that suppresses mixing of a reflected signal by causing the reflected signal itself to be output outward in the amplitude direction from the communication signal is provided. The reflected signal suppression circuit 10 is connected in series with a high side drive element Q1 and a low side drive element Q2, respectively, and prevents the reflected signal from flowing back from the communication signal to the power supply. The reflected signal suppression circuit 10 is connected in series with a high side drive element Q1 and a low side drive element Q2, respectively, and prevents the reflected signal from flowing back from the communication signal to the power supply. The reflected signal suppression circuit 10 is connected in parallel with a high side drive element Q1 and a low side drive element Q2, respectively, and adds / subtracts a voltage approximately 1.5 to 3 times the upper and lower limit values ​​of the high level voltage of the communication signal as a limiting voltage when a reflected signal flows from the communication signal.

Description

[Technical field]

[0001] The present invention relates to a communication device that suppresses reflected signals generated in a communication line along which a communication signal is transmitted. [Background technology]

[0002] Generally, in communication devices that transmit communication signals using electric wires, it is required that the impedance of the transmitting side, receiving side, and electric wire be the same. In communication lines with impedance mismatch, there is a risk that a reflected signal will be generated due to the mismatch and be mixed into the communication signal. Figure 7 shows the transmitted waveform, the received waveform including the reflected waveform, and the binarized waveform of this received waveform.

[0003] For example, if the impedance Zt of the transmitter and the wire is 50 Ω and the impedance Zr of the receiver is 1000 Ω, and the signal amplitude on the transmitter is At, the reflection coefficient (reflection amplitude) Γ (gamma) is n teeth, Gamma n = At × { (Zr - Zt) ÷ (Zr + Zt)} n ...Formula (1) Since the first reflection amplitude is n=1, Γ1= At × { (1000 - 50) ÷ (1000 + 50)} 1 = 0.90 At As a result, a reflected waveform with an amplitude of 0.90 times the signal amplitude At on the transmitting side is generated.

[0004] The reflection time t is proportional to the line length L. If the signal transmission speed in the wire is υ, then t (s) = 2L÷υ ...Equation (2) When using a typical coaxial cable or twisted pair cable, υ is approximately 2×10 8 m / s, so for example, if the length of the wire L is 100 m, the reflection time t is t = 2 × 100 ÷ (2×10 8 ) = 1×10 -6 = 1 (μs).

[0005] If this reflection amplitude Γ1 is large and the received waveform falls below the binary threshold voltage Vt, as shown in FIG. 7, it will be the same as if noise had been mixed in when the signal was demodulated on the receiving side, and this will affect the quality of communications.

[0006] Figures 8 and 9 show a conventional push-pull driven transmitter circuit, which has a communication signal drive transistor Q11, which is the high side drive element, and a communication signal drive transistor Q12, which is the low side drive element. When the communication signal is driven to a high level, Q11 is turned on by the high side drive signal, and when it is driven to a low level, Q12 is turned on by the low side drive signal. When not driving the communication signal and setting it to high impedance, both Q11 and Q12 are turned off.

[0007] Rectifier element (diode) D11 connected in parallel to transistor Q11 flows the reflected signal current to the power supply + side when it flows in from the communication signal +, protecting the transistor Q12 from exceeding its withstand voltage. The upper limit of the communication signal + voltage at that time is the sum of the power supply + and the forward voltage of diode D11. Diode D12 connected in parallel to transistor Q12 flows the reflected signal current to the communication signal - when it flows out from the communication signal +, preventing the withstand voltage of transistor Q11 from being exceeded. The lower limit of the communication signal + voltage at that time is the power supply - minus the forward voltage of diode D12.

[0008] Capacitor C11 is a bypass capacitor used to lower the high frequency impedance between power supply + and power supply -, and between power supply + and communication signal -. When a reflected signal current flows from communication signal + during high side operation, it acts to flow from communication signal + through power supply +, capacitor C11, and power supply - to communication signal -.

[0009] (20) in Figure 7 is the reflected waveform when high side drive begins. At this time, in the transmitting circuit in Figure 8, a reflected signal current flows through path (A). That is, it flows from communication signal - through capacitor C11 and transistor Q11 to communication signal +. When reflection time t has elapsed, the reflected signal on the receiving side is inverted as shown in (21), and in the transmitting circuit in Figure 8, a reflected signal current flows through path (B). That is, it flows from communication signal + through diode D11 and capacitor C11 to communication signal -. As a result, the reflected signal oscillates with amplitude Γ1, based on the voltage of the power supply +.

[0010] (22) in Figure 7 is the reflected signal when low-side drive begins. At this time, in the transmission circuit in Figure 9, the reflected signal current flows through path (B). After the reflection time t has elapsed, the reflected signal on the receiving side is inverted as shown in (23), and in the transmission circuit in Figure 9, the reflected signal current flows through path (A), so the reflected signal oscillates with an amplitude Γ1 based on the power supply - voltage.

[0011] As a result, the reflected waveform falls below the binarization threshold voltage Vt at (21) in Figure 7 and exceeds the binarization threshold voltage Vt at (23). The reflected signal crosses the binarization threshold voltage Vt at points (21) and (23), causing the binarized received waveform to be interrupted. This noise contamination causes the binarized signal to have a different value from the original communication signal.

[0012] Various countermeasures against the interference of reflected signals have been known in the past, such as performing binarization processing in anticipation of the presence of reflected waveforms when demodulating received signals (e.g., Patent Document 1) and suppressing reflected waveforms by adjusting the transmission impedance (e.g., Patent Document 2).

[0013] Also known are methods that allow normal demodulation even when there is a reflected waveform by giving the receiving circuit the ability to correct (shape) the reflected waveform (for example, Patent Document 3), and methods that reduce the reflected waveform (ringing) that occurs at the branch line branch by setting the electric wire length to a predetermined length (for example, Patent Document 4). These conventional technologies aim to improve communication quality by attempting to suppress the reflected waveform caused by impedance mismatch on the communication line or by correcting the reflected waveform on the receiving side. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] WO2008 / 038388 publication [Patent Document 2] JP 2009-296568 A [Patent Document 3] JP 2011-239091 A [Patent Document 4] JP 2016-051968 A Summary of the Invention [Problem to be solved by the invention]

[0015] However, in the above-mentioned conventional countermeasures against reflected waves, the circuit configuration becomes complicated, and whenever the length of the electric wire is changed, the circuit needs to be changed, which may make the circuit design complicated.

[0016] The present invention aims to solve the above problems and provide a communication device that can easily suppress reflected waves with a simple circuit configuration and can suppress reflected waves without requiring circuit modifications even if the length of the electric wire is changed. [Means for solving the problem]

[0017] In order to achieve the above object, a communication device according to the present invention comprises: A communication device having a push-pull driven transmission circuit having a high side drive element and a low side drive element, which transmits a communication signal in two values, high level and low level, and a reception circuit having a binary threshold voltage for distinguishing a received communication signal into a high level and a low level, the transmission circuit includes a reflected signal suppression circuit that suppresses the influence of a reflected signal generated in a communication line of the communication device on the communication signal; The reflected signal suppression circuit suppresses the reflected signal itself from being mixed in with the communication signal by directing the reflected signal outward in the amplitude direction of the communication signal, a first rectifier element and a second rectifier element connected in series with the high-side drive element and the low-side drive element, respectively, for preventing a reflected signal from flowing back from the communication signal to the power supply side; The device is provided with first and second voltage limiting elements that are connected in parallel with the high-side and low-side driving elements, respectively, and that, when a reflected signal flows from the communication signal, add or subtract a voltage that is approximately 1.5 to 3 times the upper and lower limit values ​​of the high-level voltage of the communication signal as a limiting voltage. Here, the first and second voltage limiting elements are provided to add or subtract approximately 1.5 to 3 times the voltage in order to reliably prevent a reflected signal from being mixed into the communication signal and in relation to the withstand voltage of the driving element.

[0018] According to this configuration, the reflected signal suppression circuit of the push-pull driven transmission circuit includes first and second rectifier elements connected in series with the high side and low side drive elements, respectively, and first and second voltage limiting elements connected in parallel, which add / subtract a voltage approximately 1.5 to 3 times the upper and lower limits of the high-level voltage as a limiting voltage. Therefore, the reflected signal itself is output outward in the amplitude direction of the communication signal, and does not reduce the amplitude of the communication signal. Therefore, the reflected signal does not cross the binary threshold voltage, and mixing of the reflected signal with the communication signal is prevented. As a result, the reflected signal can be easily suppressed with a simple circuit configuration, and reflected signal suppression can be performed without requiring circuit changes even if the length of the electric wire is changed, making it possible to easily transmit long distances and branch line branching.

[0019] Furthermore, the reflected signal suppression circuit may have the first rectifier element connected in series with the high side driving element to prevent a reverse flow of a positive current of a reflected signal from the communication signal to the positive side of a power supply, the second voltage limiting element connected in parallel with the low side driving element to add a voltage of approximately 1.5 to 3 times the upper limit positive value of a high-level voltage when a positive current flows from the communication signal, the second rectifier element connected in series with an output of the low side driving element to prevent a reverse flow of a negative current of a reflected signal from the communication signal to the negative side of a power supply, and the first voltage limiting element connected in parallel with the high side driving element to subtract a voltage of approximately 1.5 to 3 times the lower limit negative value of a high-level voltage when a negative current of a reflected signal flows from the communication signal. In this case, the reflected signal can be easily suppressed with a simple circuit configuration, and even if the length of the electric wire is changed, the reflected signal can be suppressed without requiring any circuit changes.

[0020] Preferably, the first and second voltage limiting elements add or subtract a voltage that is approximately twice the upper and lower limit values ​​of the high-level voltage, so that reflected signals can be easily suppressed with a simpler circuit configuration. Effect of the Invention

[0021] In the present invention, the reflected signal suppression circuit of the push-pull driven transmission circuit comprises first and second rectifier elements connected in series with the high side and low side drive elements, respectively, and first and second voltage limiting elements connected in parallel, respectively, for adding or subtracting a voltage approximately 1.5 to 3 times the upper and lower limits of the high-level voltage as a limiting voltage. Therefore, the reflected signal itself is output outward in the amplitude direction of the communication signal, and does not reduce the amplitude of the communication signal. This prevents the reflected signal from being mixed into the communication signal, and the reflected signal can be easily suppressed with a simple circuit configuration, and reflected signal suppression is possible without requiring circuit modifications even if the length of the electric wire is changed. [Brief description of the drawings]

[0022] [Figure 1] 1 is a circuit diagram showing a transmission circuit of a communication device according to an embodiment of the present invention; [Diagram 2]FIG. 2 is a circuit diagram showing the receiving circuit. [Diagram 3] 11 is a diagram showing the flow of a reflected signal during high-side driving of the transmission circuit. FIG. [Figure 4] 11 is a diagram showing the flow of a reflected signal during low-side driving of the transmission circuit. FIG. [Diagram 5] FIG. 13 is a diagram showing waveforms on the receiving side. [Figure 6] FIG. 13 is a diagram showing a waveform on the transmitting side. [Figure 7] 1A and 1B are diagrams showing a transmitted waveform, a received waveform including a conventional reflected waveform, and a binarized waveform of the received waveform. [Figure 8] FIG. 13 is a diagram showing the flow of a reflected signal during high side driving of a conventional transmission circuit. [Figure 9] FIG. 13 is a diagram showing the flow of a reflected signal during low-side driving of a conventional transmission circuit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Preferred embodiments of the present invention will now be described with reference to the drawings. Fig. 1 shows a transmission circuit 2 of a communication device 1 according to one embodiment of the present invention. The transmission circuit 2 is a push-pull output circuit having a high-side driving element, for example a PNP type communication signal driving transistor Q1, and a low-side driving element, for example an NPN type communication signal driving transistor Q2, and transmits a communication signal in two values, high level and low level.

[0024] To drive the communication signal to a high level, high side drive signal 3 is applied to B (base) of transistor Q1 to turn it on, and to drive it to a low level, low side drive signal 4 is applied to B (base) of transistor Q2 to turn it on. To not drive the signal and set it to high impedance, both transistors Q1 and Q2 are turned off.

[0025] The transmission circuit 2 includes a reflected wave suppression circuit 10 that suppresses the influence of reflected waves generated on the communication line of the communication device 1 on the communication signal. The reflected wave suppression circuit 10 includes first and second voltage limiting elements, such as Zener diodes ZD1 and ZD2, and first and second rectifying elements, such as rectifying diodes D1 and D2.

[0026] The power supply +7 is connected to the connection point of E (emitter) of transistor Q1 and K (cathode) of Zener diode ZD1. The power supply -8 is connected to the connection point of E (emitter) of transistor Q2 and A (anode) of Zener diode ZD2. The communication signal +5 is output from the connection point of K (cathode) of rectifier diode D1 and A (anode) of rectifier diode D2. The communication signal -6 is output from the connection point of E (emitter) of transistor Q2 and A (anode) of Zener diode ZD2.

[0027] The rectifier diode D1 on the high side drive side is connected in series with the connection point between C (collector) of transistor Q1 and K (cathode) of Zener diode ZD1, and prevents backflow to the power supply +7 when a positive current of the reflected signal flows in from the communication signal +5. The rectifier diode D2 on the low side drive side is connected in series with the connection point between C (collector) of transistor Q2 and K (cathode) of Zener diode ZD2, and prevents backflow to the power supply - when a current of the reflected signal flows out from the communication signal +5.

[0028] Zener diode ZD1 is connected in parallel to transistor Q1 and subtracts voltage when a reflected signal current flows out from communication signal +5, so the voltage of Zener diode ZD1 is subtracted from the voltage of power supply +7 for communication signal +5. Zener diode ZD2 is connected in parallel to transistor Q2 and adds voltage when a reflected signal current flows in from communication signal +, so the voltage of Zener diode ZD2 is added from the voltage of power supply -8 to communication signal +5.

[0029] At this time, the Zener diodes ZD1 and ZD2 preferably add or subtract a voltage approximately 1.5 to 3 times the upper and lower limits of the high-level voltage of the communication signal as a breakdown voltage (limiting voltage). In other words, the Zener diodes ZD1 and ZD2 limit the voltage to approximately 1.5 to 3 times the upper and lower limits of the high-level voltage. More preferably, they add or subtract a voltage approximately twice the upper and lower limits of the high-level voltage. The approximately 1.5 to 3 times value for the Zener diodes ZD1 and ZD2 is set to ensure that a reflected signal is not mixed into the communication signal and in relation to the withstand voltage of the driving element.

[0030] Capacitor C1 is a bypass capacitor used to lower the high frequency impedance between power supply +7 and power supply -8, and between power supply +7 and communication signal -6. When a reflected signal current flows out from communication signal +5, it flows from communication signal -6 through power supply -8, capacitor C1, and power supply +7 to communication signal +5.

[0031] Figure 2 shows a receiving circuit 20 that receives a communication signal +5 and a communication signal -6 transmitted from a transmitting circuit 2. A Zener diode ZD3 determines a binary threshold voltage Vt. Resistors R1 and R2 determine a base current to be passed through a transistor Q3. The emitter of the transistor Q3 is connected to a power supply -23, and a resistor R3 connected to a power supply +22 is connected to the collector of the transistor Q3, and this collector current is converted to a voltage to be used as a receiving signal 21.

[0032] Figure 3 shows the current flow of the reflected signal during high side drive (communication signal is high level), and Figure 4 shows the current flow of the reflected signal during low side drive (communication signal is low level). During high side drive in Figure 3, a negative current of the reflected signal flows through path (A) in the transmitting circuit 2. That is, a negative current flows from communication signal -6 through capacitor C1, transistor Q1, and rectifier diode D1 to communication signal +5. After the reflection time t has elapsed, the reflected signal on the receiving side is inverted, and a positive current of the reflected signal flows through path (B) in Figure 3. That is, a positive current flows from communication signal +5 through rectifier diode D2 and Zener diode ZD2 to communication signal -6.

[0033] During low-side driving in Figure 4, a positive current of the reflected signal flows through the path (B) in the transmitting circuit 2. That is, a positive current flows from the communication signal +5 through the rectifier diode D2 and Zener diode ZD2 to the communication signal -6. When the reflection time t has elapsed, the reflected signal on the receiving side is inverted, and a negative current of the reflected signal flows through the path (A) in Figure 4. That is, a negative current flows from the communication signal -6 through the capacitor C1, Zener diode ZD1, and rectifier diode D1 to the communication signal +5.

[0034] In the present invention, the reflected signal suppression circuit 10 of the push-pull driven transmission circuit 2 in Figure 1 uses rectifier diodes D1 and D2 connected in series with the high side and low side drive elements Q1 and Q2, respectively, as rectifier elements, and sets the breakdown voltages of Zener diodes ZD1 and ZD2, which are connected in parallel to subtract or add voltage, to approximately 1.5 to 3 times the transmission amplitude At of the communication signal, thereby achieving an operation that prevents the reflected signal from reducing the amplitude of the communication signal.

[0035] The waveform on the receiving side of the transmitter circuit 2 in Figure 3 is shown in Figure 5. For (1) and (3) in Figure 5, the reflection amplitude Γ1, where n = 1 in equation (1), and the reflection time t are determined by equation (2). The waveform on the transmitting side of the transmitter circuit 2 in Figure 3 is shown in Figure 6. For (11) in Figure 6 during high side driving, the reflected signal passes through (A) in Figure 3 and a negative current flows, so its voltage is the power supply +7 plus the forward voltage of diode D1. And for (12), the reflected signal on the receiving side arrives with a delay of the reflection time t in equation (2), and the path of the positive current passes through (B) in Figure 3, so the voltage of the communication signal + is the transmission amplitude At plus the reflection amplitude Γ2, where n = 2 in equation (1), and its maximum value is limited by the breakdown voltage of the Zener diode ZD2.

[0036] Next, in (2) of Fig. 5, the voltage of the reflected signal drops, but at the same time, the positive current of the reflected signal in (12) of Fig. 6 flows via (B) of Fig. 3, so the drop in (2) is suppressed to a certain extent in (12), and coupled with the fact that the reflected signal itself is sent outward in the amplitude direction of the communication signal, the reflected signal does not fall below the binary threshold voltage Vt, as in the conventional case in (21) of Fig. 7, and the reflected signal does not cross the binary threshold voltage Vt. Therefore, it is possible to prevent the reflected signal from being mixed into the communication signal.

[0037] In (13) of Figure 6, when the low side is driven, the positive current of the reflected signal flows via (B) of Figure 4, so its voltage is the voltage of power supply -8 minus the forward voltage of diode D2. And in (14), the reflected signal from the receiving side arrives delayed by the reflection time t in equation (2), and the path of its negative current passes via (A) of Figure 4, so the voltage of communication signal +5 is the potential difference between power supplies +7 and -8 minus the breakdown voltage of Zener diode ZD1.

[0038] Next, in (4) of Fig. 5, the voltage of the reflected signal rises, but at the same time, the negative current of the reflected signal in (14) of Fig. 6 flows via (A) of Fig. 3, so the rise in (4) is suppressed to a certain extent in (14), and coupled with the fact that the reflected signal itself is directed outward in the amplitude direction of the communication signal, the reflected signal does not exceed the binarization threshold voltage Vt as in the conventional case in (23) of Fig. 7, and the reflected signal does not cross the binarization threshold voltage Vt. Therefore, it is possible to prevent the reflected signal from being mixed into the communication signal.

[0039] As a result, in the present invention, the reflected signal suppression circuit 10 of the push-pull driven transmission circuit 2 is equipped with rectifier diodes D1, D2 connected in series with the high side and low side drive elements Q1, Q2, respectively, and Zener diodes ZD1, ZD2 connected in parallel, respectively, and adding / subtracting a voltage approximately 1.5 to 3 times the upper and lower limits of the high level voltage as a breakdown voltage. Therefore, the reflected signal itself is output outward in the amplitude direction of the communication signal, and the reflected signal does not reduce the amplitude of the communication signal. Therefore, the reflected signal does not cross the binary threshold voltage Vt, and the reflected signal is prevented from being mixed into the communication signal. As a result, the reflected signal can be easily suppressed with a simple circuit configuration, and reflected signal suppression is possible without requiring circuit modification even if the length of the electric wire is changed.

[0040] In this embodiment, Zener diodes are used as the first and second voltage limiting elements, but the present invention is not limited to this, and for example, a TVS (Transient Voltage Suppressor) or a varistor may also be used.

[0041] The present invention is not limited to the above-described embodiment, and various additions, modifications, and deletions are possible without departing from the scope of the present invention. Therefore, such modifications are also included in the scope of the present invention. [Explanation of symbols]

[0042] 1: Communication equipment 2: Transmitting circuit 3: High side drive signal 4: Low side drive signal 5: Communication signal + 6: Communication signal- 7: Power+ 8:Power- 10:Reflected signal suppression circuit 20: Receiving circuit D1, D2: First and second rectifier elements (rectifier diodes) Q1, Q2: High side drive element, low side drive element (drive transistor) Vt: binary threshold voltage ZD1, ZD2: First and second voltage limiting elements (Zener diodes) ZD3: Zener diode

Claims

1. A communication device having a push-pull driven transmission circuit having a high side drive element and a low side drive element, which transmits a communication signal in two values, high level and low level, and a reception circuit having a binary threshold voltage for distinguishing a received communication signal into a high level and a low level, the transmission circuit includes a reflected signal suppression circuit that suppresses the influence of a reflected signal generated in a communication line of the communication device on the communication signal; The reflected signal suppression circuit suppresses the ingress of the reflected signal by directing the reflected signal itself outward in the amplitude direction of the communication signal. a first rectifier element and a second rectifier element connected in series with the high-side drive element and the low-side drive element, respectively, for preventing a reflected signal from flowing back from the communication signal to the power supply side; the communication device comprising: first and second voltage limiting elements respectively connected in parallel with the high side and low side driving elements, and configured to limit upper and lower limits of a reflected signal waveform of a communication signal when a reflected signal flows from the communication signal to a limiting voltage that is approximately 1.5 to 3 times the transmission amplitude At of the communication signal.

2. In claim 1, The reflected signal suppression circuit includes: the first rectifying element is connected in series with the high side driving element to prevent a reverse flow of a positive current of a reflected signal from a communication signal to the positive side of a power supply, and the second voltage limiting element is connected in parallel with the low side driving element to suppress an upper limit positive value of the reflected signal waveform to a limiting voltage that is approximately 1.5 to 3 times the transmission amplitude At when a positive current flows from the communication signal, the second rectifying element is connected in series with the output of the low side driving element to prevent reverse flow of a negative current of a reflected signal from the communication signal to the negative side of a power supply, and the first voltage limiting element is connected in parallel with the high side driving element to limit a lower limit negative value of the reflected signal waveform to a limiting voltage approximately 1.5 to 3 times the transmission amplitude At when a negative current of a reflected signal flows from the communication signal.

3. In claim 1 or 2, A communication device, wherein the first and second voltage limiting elements limit the transmission amplitude At to approximately twice the limiting voltage.

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