COMMUNICATION SYSTEM

Abstract

The communication system includes a push-pull transmitter circuit (2) that includes a reflection signal attenuator circuit (10) configured to keep the reflection signals outside of the amplitude direction of communication signals to prevent contamination thereof. The reflection signal attenuator circuit (10) includes first and second rectifier elements (D1 and D2) connected in series to a high-side drive element and a low-side drive element (Q1 and Q2), respectively, to prevent the reflection signals from the communication signals from flowing back to a power supply side, and first and second voltage cap elements (ZD1 and ZD2) connected in parallel to the high-side drive element and the low-side drive element (Q1 and Q2), respectively, to provide (add or subtract) capping voltages equal to approximately 1.5 to 3 times upper or lower boundaries for a HIGH level voltage of the communication signals when passing the reflection signals from the communication signals therethrough.

Claims

1. A communication system comprising: a push-pull transmitter circuit including a high-side drive element and a low-side drive element to transmit communication signals having HIGH and LOW level binary values, the transmitter circuit also including a reflection signal attenuator circuit configured to attenuate an effect that reflection signals appearing on a transmission line of the communication system has on the communication signals by biasing the reflection signals outwards of an amplitude direction of the communication signals to prevent contamination thereof; and a receiver circuit configured to receive and discriminate HIGH and LOW levels of the communication signals with a binarization voltage threshold, the reflection signal attenuator circuit including: first and second rectifier elements connected in series to the high-side drive element and the low-side drive element, respectively, and configured to prevent the reflection signals from flowing back to a power supply side from the communication signals; and first and second voltage cap elements connected in parallel to the high-side drive element and the low-side drive element, respectively, and configured to add or subtract capping voltages, equal to approximately 1.5 to 3 times upper or lower boundaries for a HIGH level voltage of the communication signals, to or from the boundaries when passing the reflection signals from the communication signals therethrough.

2. The communication system as claimed in claim 1, wherein the reflection signal attenuator circuit is configured such that: the first rectifier element connected in series to the high-side drive element prevents positive electrical current of the reflection signals from flowing back to a positive supply side from the communication signals; the second voltage cap element connected in parallel to the low-side drive element adds a capping voltage equal to approximately 1.5 to 3 times a positive upper boundary for the HIGH level voltage when passing the positive electrical current from the communication signals therethrough; the second rectifier element connected in series to an output of the low-side drive element prevents negative electrical current of the reflection signals from flowing back to a negative supply side from the communication signals; and the first voltage cap element connected in parallel to the high-side drive element subtracts a capping voltage equal to approximately 1.5 to 3 times a negative lower boundary for the HIGH level voltage when passing the negative electrical current of the reflection signals from the communication signals therethrough.

3. The communication system as claimed in claim 1 or 2, wherein the first and second voltage cap elements are configured to add or subtract capping voltages equal to approximately twice the upper or lower boundaries for the HIGH level voltage.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The present invention will be more clearly understood from the following description of preferred embodiments made with reference to the accompanying drawings. However, the embodiments and the drawings are given merely for the purpose of illustration and explanation, and should not be used to delimit the scope of the present invention, which scope is to be delimited by the appended claims. In the accompanying drawings, alike numerals are assigned to and indicate alike parts throughout the different figures.

[0042] FIG. 1 is a circuit diagram of a transmitter circuit of a communication system in accordance with an embodiment of the present invention;

[0043] FIG. 2 is a circuit diagram of a receiver circuit of the communication system;

[0044] FIG. 3 illustrates how reflection signals flow during high-side driving periods of the transmitter circuit;

[0045] FIG. 4 illustrates how reflection signals flow during low-side driving periods of the transmitter circuit;

[0046] FIG. 5 illustrates a waveform on the receiver side;

[0047] FIG. 6 illustrates a waveform on the transmitter side;

[0048] FIG. 7 illustrates a transmitted waveform, a received waveform containing reflection waveforms, and a binarized result of the received waveform in accordance with a conventional example;

[0049] FIG. 8 illustrates how reflection signals flow during high-side driving periods of a conventional transmitter circuit; and

[0050] FIG. 9 illustrates how reflection signals flow during low-side driving periods of the conventional transmitter circuit.

DESCRIPTION OF EMBODIMENTS

[0051] What follows is a description of preferred embodiments of the present invention, made with reference to the drawings. FIG. 1 depicts a transmitter circuit 2 of a communication system 1 in accordance with an embodiment of the present invention. The transmitter circuit 2 is in the form of a push-pull output circuit that includes a high-side drive element (e.g., a communication signal drive PNP transistor Q1) and a low-side drive element (e.g., a communication signal drive NPN transistor Q2) to transmit communication signals having HIGH and LOW level binary values.

[0052] To drive a communication signal at HIGH level, a high-side drive signal 3 is applied to a base B of the transistor Q1 to turn on the transistor Q1. To drive a communication signal at LOW level, a low-side drive signal 4 is applied to a base B of the transistor Q2 to turn on the transistor Q2. Both the transistor Q1 and the transistor Q2 are switched off when it is wished to create a non-activated state having a high impedance.

[0053] The transmitter circuit 2 includes a reflection wave attenuator circuit 10 configured to attenuate an effect that reflection waves appearing on a transmission line of the communication system 1 has on the communication signals. The reflection wave attenuator circuit 10 includes first and second voltage cap elements (e.g., Zener diodes ZD1 and ZD2) and first and second rectifier elements (e.g., rectifier diodes D1 and D2).

[0054] A positive supply 7 is connected to the junction between an emitter E of the transistor Q1 and a cathode K of the Zener diode ZD1. A negative supply 8 is connected to the junction between an emitter E of the transistor Q2 and an anode A of the Zener diode ZD2. A positive communication signal 5 is output via the junction between a cathode K of the rectifier diode D1 and an anode A of the rectifier diode D2. A negative communication signal 6 is output via the junction between the emitter E of the transistor Q2 and the anode A of the Zener diode ZD2.

[0055] The high-side drive rectifier diode D1 is connected in series to the junction between a collector C of the transistor Q1 and an anode A of the Zener diode ZD1 to prevent positive electrical current of the reflection signals flowing in via the positive communication signal 5 side from flowing back to the positive power supply 7 side. The low-side drive rectifier diode D2 is connected in series to the junction between a collector C of the transistor Q2 and a cathode K of the Zener diode ZD2 to prevent negative electrical current of the reflection signals flowing in via the positive communication signal 5 side from flowing back to the negative power supply 8 side.

[0056] The Zener diode ZD1 is connected in parallel to the transistor Q1 for voltage subtraction when negative electrical current of reflection signals flows in via the positive communication signal 5 side, such that the voltage of the positive supply 7 minus the voltage across the Zener diode ZD1 is applied to the positive communication signal 5. The Zener diode ZD2 is connected in parallel to the transistor Q2 for voltage addition when positive electrical current of reflection signals flows out via the positive communication signal 5 side, such that the voltage of the negative supply 8 plus the voltage across the Zener diode ZD2 is applied to the positive communication signal 5.

[0057] Here, the Zener diodes ZD1 and ZD2 are configured to provide capping voltages or to add or subtract a breakdown voltage to or from the upper or lower boundary for a HIGH level voltage of the communication signals, the breakdown voltage to be a capping voltage that is preferably equal to approximately 1.5 to 3 times the boundary (e.g., voltage). In other words, the Zener diodes ZD1 and ZD2 are configured to keep voltages within approximately 1.5 to 3 times the upper or lower boundaries for the HIGH level voltage. More preferably, they are configured to provide capping voltages equal to approximately twice the upper or lower boundaries for the HIGH level voltage. Approximately 1.5 to 3 times the boundaries are chosen for the Zener diodes ZD1 and ZD2 to ensure that the communication signals are not contaminated with the reflection signals or in consideration of the withstand voltages of the drive elements.

[0058] A capacitor C1 is a bypass capacitor used to provide reduced high-frequency impedance between the positive supply 7 side and the negative supply 8 side and between the positive supply 7 side and the negative communication signal 6 side. And it acts to pass electrical current of reflection signals flowing out via the positive communication signal 5 side, from the negative communication signal 6 side to the positive communication signal 5 side through the negative supply 8 side, the capacitor C1, and the positive supply 7 side.

[0059] FIG. 2 depicts a receiver circuit 20 configured to receive positive communication signals 5 and negative communication signals 6 transmitted by the transmitter circuit 2. A Zener diode ZD3 determines a binarization voltage threshold Vt. Resistors R1 and R2 determine a base current that flows to a transistor Q3. An emitter of the transistor Q3 is connected to a negative supply 23, and a resistor R3 coupled to a positive supply 22 is connected to a collector of the transistor Q3 to generate a voltage thereacross with a collector current to provide a received signal 21.

[0060] FIG. 3 illustrates how electrical current of reflection signals flows during high-side driving periods (when the communication signals have a HIGH level), and FIG. 4 illustrates how electrical current of reflection signals flows during low-side driving periods (when the communication signals have a LOW level). During high-side driving periods, negative electrical current of reflection signals flows through the transmitter circuit 2 of FIG. 3 along the route (A). That is, the negative electrical current flows from the negative communication signal 6 side to the positive communication signal 5 side through the capacitor C1, the transistor Q1, and the rectifier diode D1. As the reflection time t elapses, the reflection signals flip on the receiver side, so that positive electrical current of the reflection signals flows in FIG. 3 along the route (B). That is, the positive electrical current passes from the positive communication signal 5 side to the negative communication signal 6 side through the rectifier diode D2 and the Zener diode ZD2.

[0061] During low-side driving periods, positive electrical current of reflection signals flows through the transmitter circuit 2 of FIG. 4 along the route (B). That is, the positive electrical current flows from the positive communication signal 5 side to the negative communication signal 6 side through the rectifier diode D2 and the transistor Q2. As the reflection time t elapses, the reflection signals flip on the receiver side, so that negative electrical current of the reflection signals flows in FIG. 4 along the route (A). That is, the negative electrical current passes from the negative communication signal 6 side to the positive communication signal 5 side through the capacitor C1, the Zener diode ZD1, and the rectifier diode D1.

[0062] According to the present invention, the reflection signal attenuator circuit 10 of the push-pull transmitter circuit 2 in FIG. 1 prevents reflection signals from jeopardizing the amplitude of the communication signals with a simple circuit configuration that uses rectifier diodes D1 and D2 connected in series to high-side and low-side drive elements Q1 and Q2, respectively, as rectifier elements and with a simple circuit configuration that has Zener diodes ZD1 and ZD2 connected in parallel to the high-side and low-side drive elements Q1 and Q2, respectively, to add and subtract voltages and that breakdown voltages (capping voltages) of them are set to approximately 1.5 to 3 times the transmission amplitude At of the communication signals.

[0063] FIG. 5 depicts a waveform on the receiver side according to the transmitter circuit 2 of FIG. 3. The points (1) and (3) in FIG. 5 have a reflection amplitude .sub.1 determined according to equation (1) (where n=1) and a reflection time t determined according to equation (2). FIG. 6 depicts a waveform on the transmitter side according to the transmitter circuit 2 of FIG. 3. Negative electrical current of the reflection signals flows at the point (11) in FIG. 6 during a high-side driving period via the route (A) in FIG. 3, generating a voltage that is equal to the positive supply 7 plus the forward voltage of the diode D1. At the point (12), the reflection signals from the receiver side arrives after the reflection time t according to equation (2), and positive electrical current of it flows via the route (B) in FIG. 3, adding a reflection amplitude .sub.2 (where n=2) according to equation (1) to the transmission amplitude At of the voltage of a positive communication signal with the maximum of it being capped by the breakdown voltage of the Zener diode ZD2.

[0064] Then, at the point (2) in FIG. 5, the voltage of the reflection signals drops while at the same time the positive electrical current of the reflection signals at the point (12) in FIG. 6 flows via the route (B) in FIG. 3. Hence, the drop at the point (2) is counteracted to some degree at the point (12). In combination with the fact that the reflection signals are biased outwards of the amplitude direction of the communication signals, this ensures that the reflection signals do not dip below the binarization voltage threshold Vt and prevents reflection signals from crossing the binarization voltage threshold Vt unlike the point (21) in FIG. 7 which illustrating a conventional example. Accordingly, the reflection signals can be kept from contaminating the communication signals.

[0065] Positive electrical current of the reflection signals flows at the point (13) in FIG. 6 during a low-side driving period via the route (B) in FIG. 4, generating a voltage that is equal to the negative supply 8 minus the forward voltage of the diode D2. At the point (14), the reflection signals from the receiver side arrives after the reflection time t according to equation (2), and negative electrical current of it flows via the route (A) in FIG. 4, resulting in the voltage of the positive communication signal 5 corresponding to the potential difference between the positive supply 7 and the negative supply 8 minus the breakdown voltage of the Zener diode ZD1.

[0066] Then, at the point (4) in FIG. 5, the voltage of the reflection signals rises while at the same time the negative electrical current of the reflection signals at the point (14) in FIG. 6 flows via the route (A) in FIG. 3. Hence, the rise at the point (4) is counteracted to some degree at the point (14). In combination with the fact that the reflection signals are biased outwards of the amplitude direction of the communication signals, this ensures that the reflection signals do not rise above the binarization voltage threshold Vt and prevents reflection signals from crossing the binarization voltage threshold Vt unlike the point (23) in FIG. 7 which illustrating a conventional example. Accordingly, the reflection signals can be kept from contaminating communication signals.

[0067] Thus, according to the present invention, the reflection signal attenuator circuit 10 of the push-pull transmitter circuit 2 includes rectifier diodes D1 and D2 connected in series to the high-side drive element Q1 and the low-side drive element Q2, respectively, as well as Zener diodes ZD1 and ZD2 connected in parallel to the high-side drive element Q1 and the low-side drive element Q2, respectively, to add or subtract breakdown voltages (to provide capping voltages) equal to approximately 1.5 to 3 times upper or lower boundaries for a HIGH level voltage. This will bias the reflection signals outwards of the amplitude direction of the communication signals to prevent the amplitude of the communication signals from being jeopardized by the reflection signals, thereby keeping the reflection signals from crossing the binarization voltage threshold Vt and from contaminating the communication signals. In this way, attenuation of reflection signals can be easily achieved with a simple circuit configuration with no need for circuit changes when a different electrical line length is used.

[0068] It should be noted that while Zener diodes are used as the first and second voltage cap elements in the preceding embodiment, examples of the first and second voltage cap elements are not limited thereto but can also include TVSs (or transient voltage suppressors) and varistors.

[0069] While preferred features for carrying out the present invention thus have been discussed on the basis of embodiments with reference to the drawings, the embodiments disclosed herein should be considered illustrative and not restrictive in all respects. The scope of the present invention is to be defined not by the foregoing description but by the claims. A person skilled in the art would readily conceive of a variety of changes and modifications within the scope of obviousness in light of the disclosure herein. Accordingly, such changes and modifications are considered to come within the scope of the invention delimited by the claims or breadth of equivalency thereof.

REFERENCE SYMBOLS

[0070] 1 . . . communication system [0071] 2 . . . transmitter circuit [0072] 3 . . . high-side drive signal [0073] 4 . . . low-side drive signal [0074] 5 . . . positive communication signal [0075] 6 . . . negative communication signal [0076] 7 . . . positive supply [0077] 8 . . . negative supply [0078] 10 . . . reflection signal attenuator circuit [0079] 20 . . . receiver circuit [0080] D1, D2 . . . first and second rectifier elements (rectifier diodes) [0081] Q1, Q2 . . . high-side drive element, low-side drive element (drive transistors) [0082] Vt . . . binarization voltage threshold [0083] ZD1, ZD2 . . . first and second voltage cap elements (Zener diodes) [0084] ZD3 . . . Zener diode