Communication equipment

Abstract

The present invention provides a communication device that can easily suppress reflected signals with a simple circuit configuration, and that can suppress reflected signals without requiring circuit modifications even when the wire length is changed. [Solution] In the push-pull driven transmission circuit 2 of the communication device 1, the reflected signal suppression circuit 10, which suppresses the intrusion of the reflected signal by causing the reflected signal itself to be emitted outward in the amplitude direction from the communication signal, comprises first and second rectifier elements D1 and D2 connected in series with the high-side drive element Q1 and the low-side drive element Q2, respectively, to prevent the reflected signal from flowing back from the communication signal to the power supply side, and first and second voltage limiting elements ZD1 and ZD2 connected in parallel with the high-side drive element Q1 and the low-side drive element Q2, respectively, which add or subtract a voltage approximately 1.5 to 3 times the value 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 for transmitting communication signals.

Background Art

[0002] Generally, in a communication device that transmits communication signals using an electric wire, it is required that the impedance of the transmission side, the reception side, and the electric wire match. In a communication line with such impedance mismatch, reflected signals may be generated due to the mismatch and混入 the communication signals. Fig. 7 shows a transmission waveform, a reception waveform including a reflected waveform, and a waveform obtained by binarizing this reception waveform.

[0003] For example, when the impedance Zt of the transmission side and the electric wire is 50Ω and the impedance Zr of the reception side is 1000Ω, assuming the signal amplitude of the transmission side is At, the reflection coefficient (reflected amplitude) Γ (gamma) n is Γ n = At × { (Zr - Zt) ÷ (Zr + Zt)} n ……Equation (1) Since the first reflected amplitude is n = 1, Γ1= At × { (1000 - 50) ÷ (1000 + 50)} 1 = 0.90 At That is, a reflected waveform 0.90 times the signal amplitude At of the transmission side is generated.

[0004] The reflection time t is proportional to the line length L, and assuming the signal transmission speed in the electric wire is υ, t (s) = 2L÷υ ……Equation (2) When using a general coaxial cable or twisted pair cable, υ is about 2×10 8 m / s. Therefore, for example, when the electric wire length L is 100m, 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 binarization threshold voltage Vt, as shown in Figure 7, it is equivalent to noise being introduced when the signal is demodulated on the receiving side, affecting the quality of communication.

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

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

[0008] Capacitor C11 is a bypass capacitor designed to reduce high-frequency impedance between the power supply + and power supply -, and between power supply + and communication signal -. When high-side drive occurs and current from the reflected signal flows in from communication signal +, it directs the current from communication signal + through power supply +, capacitor C11, and power supply - to communication signal -.

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

[0010] (22) in Figure 7 is the reflected signal at the start of low-side driving. At this time, the current for the reflected signal flows through path (B) in the transmitting circuit of Figure 9. After the reflection time t has elapsed, the reflected signal on the receiving side is inverted as in (23), and the current for the reflected signal flows through path (A) in the transmitting circuit of Figure 9, so the reflected signal oscillates with amplitude Γ1 with respect to the voltage of power supply -.

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

[0012] Various countermeasures against the intrusion of this reflected signal have been known for some time. For example, it is known to perform binarization processing that anticipates the presence of the reflected waveform when demodulating the received signal (for example, Patent Document 1), or to suppress the reflected waveform by adjusting the transmission impedance (for example, Patent Document 2).

[0013] Furthermore, methods are known for giving the receiving circuit characteristics to correct (shape) reflected waveforms, thereby enabling normal demodulation even in the presence of reflected waveforms (e.g., Patent Document 3), and for reducing reflected waveforms (ringing) generated at branch lines by setting the wire length to a predetermined length (e.g., Patent Document 4). These conventional technologies aim to improve communication quality by attempting to suppress reflected waveforms due to impedance mismatch on the communication line or by correcting reflected waveforms on the receiving side. [Prior art documents] [Patent Documents]

[0014] [Patent Document 1] WO2008 / 038388 publication [Patent Document 2] Japanese Patent Publication No. 2009-296568 [Patent Document 3] Japanese Patent Publication No. 2011-239091 [Patent Document 4] Japanese Patent Publication No. 2016-051968 [Overview of the project] [Problems that the invention aims to solve]

[0015] However, with the conventional reflected wave countermeasures described above, the circuit configuration became complex, and if the wire length was changed, the circuit had to be modified each time, which sometimes made the circuit design cumbersome.

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

[0017] To achieve the aforementioned objective, the communication device according to the present invention is A communication device having a high-side drive element and a low-side drive element, a push-pull drive transmission circuit that transmits a communication signal in binary of a high level and a low level, and a reception circuit having a binary threshold voltage that distinguishes the received communication signal into a high level and a low level, The transmission circuit includes a reflection signal suppression circuit that suppresses the influence of a reflection signal generated on a communication line of the communication device on the communication signal, The reflection signal suppression circuit causes the reflection signal itself to be emitted outward in the amplitude direction of the communication signal to suppress its mixing, First and second rectifying elements connected in series with the high-side and low-side drive elements respectively to prevent the backward flow of the reflection signal from the communication signal to the power supply side, First and second voltage limiting elements connected in parallel with the high-side and low-side drive elements respectively, and when a reflection signal flows from the communication signal, adding and subtracting a voltage approximately 1.5 to 3 times that value as a limiting voltage to the upper and lower limit values of the high-level voltage of the communication signal. Here, the first and second voltage limiting elements are provided to add and subtract a voltage approximately 1.5 to 3 times in order to prevent the reflection signal from being surely mixed into the communication signal and due to the relationship of the withstand voltage of the drive element.

[0018] According to this configuration, the reflection signal suppression circuit of the push-pull drive transmission circuit includes first and second rectifying elements connected in series with the high-side and low-side drive elements respectively, and first and second voltage limiting elements connected in parallel and adding and subtracting a voltage approximately 1.5 to 3 times as a limiting voltage to the upper and lower limit values of the high-level voltage. Therefore, the reflection signal itself is emitted outward in the amplitude direction of the communication signal so that the reflection signal does not reduce the amplitude of the communication signal. As a result, the reflection signal does not cross the binary threshold voltage, the mixing of the reflection signal into the communication signal is suppressed, the reflection signal can be easily suppressed with a simple circuit configuration, and the reflection signal can be suppressed without requiring circuit modification even when the wire length is changed, enabling easy long-distance transmission and branch of the branch line.

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

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

[0021] The present invention provides a reflection signal suppression circuit for a push-pull driven transmitting circuit that includes first and second rectifier elements connected in series with the high-side and low-side driving elements, respectively, and first and second voltage limiting elements connected in parallel with each other, which add or subtract a voltage approximately 1.5 to 3 times the upper and lower limits of the high-level voltage as limiting voltages. As a result, the reflection signal itself is directed outward in the amplitude direction of the communication signal, preventing the reflection signal from reducing the amplitude of the communication signal. This suppresses the mixing of the reflection signal into the communication signal, allowing for easy reflection signal suppression with a simple circuit configuration, and enabling reflection signal suppression without the need for circuit changes even when the wire length is changed. [Brief explanation of the drawing]

[0022] [Figure 1] This is a circuit diagram showing the transmission circuit of a communication device according to one embodiment of the present invention. [Figure 2]This is a circuit diagram showing the receiving circuit. [Figure 3] This figure shows the flow of reflected signals when the high-side is driven in the same transmitting circuit. [Figure 4] This figure shows the flow of reflected signals when the low-side drive of the same transmission circuit is activated. [Figure 5] This diagram shows the waveform on the receiving end. [Figure 6] This is a diagram showing the waveform on the transmitting side. [Figure 7] This figure shows the transmitted waveform, the received waveform including the conventional reflected waveform, and the waveform obtained by binarizing the received waveform. [Figure 8] This diagram shows the flow of reflected signals during high-side drive in a conventional transmission circuit. [Figure 9] This diagram shows the flow of reflected signals when the low side is driven in a conventional transmission circuit. [Modes for carrying out the invention]

[0023] Preferred embodiments of the present invention will be described below with reference to the drawings. Figure 1 shows a transmission circuit 2 of a communication device 1 according to one embodiment of the present invention. This 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 the communication signal in binary form, high level and low level.

[0024] To drive the communication signal to a high level, the high-side drive signal 3 is applied to the base (B) of transistor Q1 to turn it on. To drive it to a low level, the low-side drive signal 4 is applied to the base (B) of transistor Q2 to turn it on. To make it high impedance without driving, both transistors Q1 and Q2 are turned off.

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

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

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

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

[0029] In this case, Zener diodes ZD1 and ZD2 add or subtract a voltage preferably 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, Zener diodes ZD1 and ZD2 suppress 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 2 times the upper and lower limits of the high-level voltage. This value of approximately 1.5 to 3 times for Zener diodes ZD1 and ZD2 is set to ensure that reflected signals are not mixed into the communication signal and due to the voltage withstand capability of the driving element.

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

[0031] Figure 2 shows the receiving circuit 20 that receives communication signals +5 and -6 transmitted from the transmitting circuit 2. The Zener diode ZD3 determines the binarization threshold voltage Vt. Resistors R1 and R2 determine the base current flowing through transistor Q3. The emitter of transistor Q3 is connected to power supply -23, and resistor R3, which is connected to power supply +22, is connected to the collector of transistor Q3. This collector current is converted into a voltage to obtain the received signal 21.

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

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

[0034] In this invention, the reflection signal suppression circuit 10 of the push-pull driven transmitting circuit 2 shown in Figure 1 uses rectifier diodes D1 and D2, respectively, connected in series with the high-side and low-side driving elements Q1 and Q2, as rectifier elements, and sets the breakdown voltage of the Zener diodes ZD1 and ZD2, respectively, connected in parallel to subtract or add voltage, to approximately 1.5 to 3 times the transmission amplitude At of the communication signal. This simple circuit configuration achieves operation in which the reflection signal does not reduce the amplitude of the communication signal.

[0035] Figure 5 shows the waveform on the receiving side in the transmitting circuit 2 of Figure 3. In Figure 5 (1) and (3), the reflection amplitude Γ1 is determined by equation (1) where n=1, and the reflection time t is determined by equation (2). Figure 6 shows the waveform on the transmitting side in the transmitting circuit 2 of Figure 3. In Figure 6 (11) during high-side drive, the reflected signal passes through (A) in Figure 3, causing a negative current to flow, so its voltage is the power supply +7 plus the forward voltage of diode D1. Then, in (12), the reflected signal on the receiving side arrives with a delay of the reflection time t given by equation (2), and the path of its 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 Zener diode ZD2.

[0036] Next, in Figure 5 (2), the voltage of the reflected signal decreases, but at the same time, the positive current of the reflected signal in Figure 6 (12) flows through Figure 3 (B). Therefore, the decrease in (2) is suppressed to a certain extent at (12), and combined with the fact that the reflected signal itself is directed outward in the amplitude direction of the communication signal, the reflected signal does not fall below the binarization threshold voltage Vt, as in the conventional Figure 7 (21), and the reflected signal does not cross the binarization threshold voltage Vt. Thus, the mixing of the reflected signal into the communication signal can be suppressed.

[0037] In Figure 6 (13) during low-side drive, the positive current of the reflected signal flows through Figure 4 (B), so its voltage is the power supply -8 minus the forward voltage of diode D2. Then, in (14), the reflected signal on the receiving side arrives with a delay of the reflection time t given by equation (2), and the path of its negative current goes through Figure 4 (A), so the voltage of the communication signal +5 is the potential difference between power supply +7 and power supply -8 minus the breakdown voltage of Zener diode ZD1.

[0038] Next, in (4) of Figure 5, the voltage of the reflected signal increases, but at the same time, the negative current of the reflected signal in (14) of Figure 6 flows through (A) of Figure 3. Therefore, the increase in (4) is suppressed to a certain extent by (14), and combined with the fact that the reflected signal itself is directed outward in the amplitude direction of the communication signal, it does not exceed the reflected signal binarization threshold voltage Vt, as in (23) of the conventional Figure 7, and the reflected signal does not cross the binarization threshold voltage Vt. Thus, the mixing of the reflected signal into the communication signal can be suppressed.

[0039] As a result, in this invention, the reflection signal suppression circuit 10 of the push-pull driven transmitting circuit 2 includes rectifier diodes D1 and D2 connected in series with the high-side and low-side driving elements Q1 and Q2, respectively, and Zener diodes ZD1 and ZD2 connected in parallel with each other, which add or subtract a voltage of approximately 1.5 to 3 times the upper and lower limits of the high-level voltage as a breakdown voltage. Therefore, the reflection signal itself is directed outward in the amplitude direction of the communication signal, and the reflection signal does not reduce the amplitude of the communication signal. Consequently, the reflection signal does not cross the binarization threshold voltage Vt, and the mixing of the reflection signal into the communication signal is suppressed. This allows for easy suppression of the reflection signal with a simple circuit configuration, and reflection signal suppression is possible even if the wire length is changed without requiring circuit modification.

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

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

[0042] 1: Communication equipment 2: Transmitter Circuit 3: High-side drive signal 4: Low-side drive signal 5: Communication signal + 6: Communication signals - 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: Binarization threshold voltage ZD1, ZD2: First and second voltage limiting elements (Zener diodes) ZD3: Zener diode

Claims

1. A communication device comprising a push-pull driven transmitting circuit having a high-side driving element and a low-side driving element, which transmits a communication signal in two values, high-level and low-level, and a receiving circuit having a binarization threshold voltage that distinguishes the received communication signal into high-level and low-level, The transmission circuit includes a reflection signal suppression circuit that suppresses the influence of reflection signals generated in the communication line of the communication device on the communication signal. The aforementioned reflected signal suppression circuit works by directing the reflected signal itself outward in the amplitude direction of the communication signal to suppress its interference. First and second rectifier elements are connected in series with the high-side and low-side drive elements, respectively, to prevent the reflected signal from flowing back from the communication signal to the power supply side. A communication device comprising first and second voltage limiting elements, each connected in parallel to the high-side and low-side driving elements, which, when a reflected signal flows from a communication signal, add or subtract a voltage approximately 1.5 to 3 times the value of the high-level voltage of the communication signal as a limiting voltage to the upper and lower limits of the high-level voltage of the communication signal.

2. In claim 1, The aforementioned reflected signal suppression circuit is The first rectifier element is connected in series with the high-side drive element to prevent the reverse flow of positive current of the reflected signal from the communication signal to the positive side of the power supply, and the second voltage limiting element is connected in parallel with the low-side drive element to add a voltage approximately 1.5 to 3 times the positive value of the upper limit of the high-level voltage when a positive current flows from the communication signal. A communication device wherein the second rectifier element is connected in series with the output of the low-side drive element to prevent the negative current of the reflected signal from flowing back from the communication signal to the negative side of the power supply, and the first voltage limiting element is connected in parallel with the high-side drive element to subtract the voltage of the reflected signal from the communication signal to approximately 1.5 to 3 times the negative value of the lower limit of the high-level voltage.

3. In claim 1 or 2, The first and second voltage limiting elements add to or subtract from the high-level voltage to approximately twice the upper and lower limits of the communication device.

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