CAN transceiver

Abstract

A transceiver is disclosed. The transceiver includes a first receiver line, a first transmitter line, a second receiver line, and a second transmitter line, wherein the first receiver line and the second receiver line are coupled to a receiver line selector, and the first transmitter line and the second transmitter line are coupled to a transmitter line selector. A system monitor is included, the system monitor is configured to monitor a controller area network (CAN) bus and the first transmitter line, and select the second transmitter line and the second receiver line if an error condition is detected by the monitoring of the first transmitter line. A bias voltage generator is included, the voltage generator generates a bias voltage for a termination capacitor of the CAN bus, wherein the bias voltage generator is activated by the system monitor when an error condition is detected in the CAN bus.

Description

Technical Field

[0001] The present invention relates to a CAN transceiver. Background Art

[0002] Controller Area Network (CAN bus) is a vehicle bus standard designed to allow microcontrollers and devices to communicate with each other's applications without a host. The controller area network is a message-based protocol originally designed for multi-channel wires in cars to save copper, but can also be used in many other situations. For each device, the data in the packet is transmitted in sequence, but in such a way that if more than one device transmits at the same time, the highest priority device can continue, while the other devices fall back. The packet is received by all devices, including by the transmitting device. The CAN bus uses twisted pairs, one of which is CANH and the other is CANL. For some reason, these wires may not be welded and may show intermittent open circuits, which may cause bit errors and may cause data communication interruptions. In addition, microcontrollers using the CAN bus may fail and cause safety issues. One way to solve the reliability problem of the CAN bus and other components on the CAN bus is to provide redundancy. However, providing parallel redundant CAN buses, transceivers, chokes that couple transceivers to the CAN bus, etc. may increase the cost, maintenance and complexity of the communication system. Summary of the invention

[0003] This summary is used to introduce a series of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

[0004] In one embodiment, a transceiver is disclosed. The transceiver includes a first receiver line, a first transmitter line, a second receiver line, and a second transmitter line, wherein the first receiver line and the second receiver line are coupled to a receiver line selector, and the first transmitter line and the second transmitter line are coupled to a transmitter line selector. A system monitor is included, the system monitor is configured to monitor a controller area network (CAN) bus and the first transmitter line, and select the second transmitter line and the second receiver line if an error condition is detected by the monitoring of the first transmitter line. A bias voltage generator is included, the voltage generator generates a bias voltage for a termination capacitor of the CAN bus, wherein the bias voltage generator is activated by the system monitor when an error condition is detected in the CAN bus.

[0005] In some examples, the system monitor is further configured to monitor the first receiver line for the error condition and select the second transmitter line and the second receiver line via the receiver line selector and the transmitter line selector. The receiver line selector and the transmitter line selector are configured to operate simultaneously. The transceiver may include an enable circuit configured to disable communication to the CAN bus, wherein the enable circuit includes two series switches that operate simultaneously to disconnect power to the CANL pin.

[0006] In some embodiments, a voltage regulating circuit may be included. The voltage regulating circuit is configured to generate a bias voltage for the termination end of the CAN bus when an open-circuit wire in the CAN bus is detected to allow communication with the CAN bus using a wire. The system monitor may include a CAN bus error detector, the CAN bus error detector including a first comparator, a first resistor, and a second resistor, wherein the first comparator is connected across the second resistor and the end of the first resistor is connected to the CANH pin. In another example, the system monitor may include a CAN bus error detector, the CAN bus error detector including a first comparator, a first resistor, and a second resistor, wherein the first comparator is connected across the second resistor and the end of the first resistor is connected to the CANL pin. The CAN bus error detector may include a configurable voltage source, the configurable voltage source including a first group of resistors coupled to a first switch and a second group of resistors coupled to a second switch. The first switch and the second switch are configured to bypass one or more resistors in a plurality of resistors based on a control signal.

[0007] In some examples, the bias voltage is 1V or 4V, depending on the error condition. In some embodiments, the transceiver may include a pair of slope controllers coupled together by a plurality of transistors and a plurality of diodes. The pair of slope controllers are operated by the system monitor to provide a differential voltage to the CANH pin and the CANL pin. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] In order that the manner in which the above-described features of the invention may be understood in detail, a more particular description of the invention briefly summarized above may be made by reference to embodiments, some of which are illustrated in the accompanying drawings. It should be noted, however, that the drawings illustrate only typical embodiments of the invention and, therefore, should not be considered to limit the scope of the invention, as the invention may admit of other equally effective embodiments. The advantages of the claimed subject matter will become apparent to those skilled in the art reading this description in conjunction with the accompanying drawings, in which like reference numerals are used to refer to like elements, and in which:

[0009] Figure 1 Depicting a controller area network (CAN) bus with termination end capacitors according to one or more embodiments of the present disclosure;

[0010] Figure 2 Depicts the CAN bus communication protocol, showing the representation of "0" and "1" based on the differential voltage at CANH and CANL;

[0011] Figure 3 A transceiver according to one or more embodiments of the present disclosure is shown; Figure 4 A schematic diagram showing a circuit for regulating the voltage at a termination capacitor of a CAN bus according to one or more embodiments of the present disclosure;

[0012] Figure 5 A schematic diagram showing a circuit for generating a variable voltage at a terminating capacitor of a CAN bus to overcome an intermittent open CANH or CANL wire in accordance with one or more embodiments of the present disclosure.

[0013] Figure 6 A schematic diagram showing a circuit for generating a variable voltage to be applied at CANH or CANL to overcome an intermittent open CANH or CANL wire according to one or more embodiments of the present disclosure;

[0014] Figure 7 illustrates an example implementation of a transmission enabling module according to one or more embodiments of the present disclosure; and

[0015] Figure 8 A transceiver according to one or more embodiments of the present disclosure is shown; and

[0016] Fig. 9 Describes a device having one or more embodiments according to the present disclosure Figure 2 The transceiver of the CAN bus.

[0017] It should be noted that the figures are not necessarily drawn to scale. Not all components in the transceiver are shown. The omitted components are known to those skilled in the art. DETAILED DESCRIPTION

[0018] Many well-known manufacturing steps, components, and connectors have been omitted or not described in detail in the description to avoid obscuring the present disclosure.

[0019] It will be readily appreciated that the components of the embodiments generally described herein and illustrated in the accompanying drawings may be arranged and designed in a variety of different configurations. Therefore, the following more detailed description of the various embodiments represented in the figures is not intended to limit the scope of the present disclosure, but is merely representative of the various embodiments. Although various aspects of the embodiments are presented in the drawings, the drawings are not necessarily drawn to scale unless specifically indicated.

[0020] The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics of the present invention. The described embodiments are considered in all respects to be illustrative only and not restrictive. Therefore, the scope of the present invention is indicated by the appended claims rather than by the specific embodiments thereof. All changes within the meaning and scope of the equivalents of the claims are included within the scope of the claims.

[0021] References throughout this specification to features, advantages, or similar language do not imply that all features and advantages that may be achieved with the present invention are or are included in any single embodiment of the present invention. Rather, language referring to features and advantages should be understood to mean that a specific feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment of the present invention. Thus, discussion of features and advantages and similar language throughout this specification may, but does not necessarily, refer to the same embodiment.

[0022] In addition, the described features, advantages and characteristics of the present invention may be combined in any suitable manner in one or more embodiments. In view of the description herein, those skilled in the relevant art will recognize that the present invention may be practiced without one or more of the specific features or advantages of a particular embodiment. In other cases, additional features and advantages may be identified in certain embodiments that may not be present in all embodiments of the present invention.

[0023] Reference throughout this specification to "one embodiment," "an embodiment," "an example," or similar language means that a particular feature, structure, or characteristic described in connection with the indicated embodiment is included in at least one embodiment of the present invention. Thus, the phrases "in one embodiment," "in an embodiment," and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

[0024] Figure 1Describe a controller area network (CAN) bus 100 with a termination end capacitor 108. The CAN bus 100 includes a twisted pair 106. The twisted pair 106 includes a CANH conductor and a CANL conductor. The CAN bus 100 may include one or more communication nodes 104-1..104-N. The capacitor 108 is typically 4.7nF. The value of the capacitor 108 may be increased to approximately 100nF. By increasing the value of the capacitor 108, the signal voltage at the CANL or CANH during intermittent open circuits can be improved. However, the improvement in the signal voltage is not sufficient for reliable communication during intermittent open circuits. The resistors coupled to the capacitor 108 are typically 60 ohms each.

[0025] As shown, communication nodes (ECUs) 104-1 ... 104-N are connected via unshielded twisted pair 106. Termination is implemented at the far left and far right of the CAN bus 100. There are two options: by using a single resistor as shown on the left side of the CAN bus 100, or via two resistors and capacitors 108, known as "split termination," as shown on the right side of the CAN bus 100. The latter approach is usually used because it provides additional low-pass filtering to improve EMC performance.

[0026] like Figure 2 As shown, in normal operation (when there is no error), the CAN bus 100 uses signals to indicate that CANH and CANL are driven so that a differential voltage is generated (to send a dominant signal) or no differential signal is generated (to send a recessive bit). For a dominant bit ("0"), the voltage at CANL is about 1.5V and the voltage at CANH is 3.5V, and V diff Represents the difference between the voltage at CANH and the voltage at CANL.

[0027] In some examples, the following error conditions may cause communication on the CAN bus 100 to be interrupted.

[0028] 1. The wire on CANH or CANL is open

[0029] 2. The wire on CANH or CANL is intermittently open

[0030] 3. Open connection contact at CANH or CANL

[0031] 4. Intermittent open connection at CANH or CANL

[0032] 5. Open solder joint contact at CANH or CANL

[0033] 6. Intermittent open solder joint contact at CANH or CANL

[0034] 7. Open solder joint contact at TXDL or RXDL at the microcontroller

[0035] 8. Intermittent open solder joint contacts at TXDL or RXDL at the microcontroller

[0036] 9. Open solder joint contact at TXDL or RXDL at transceiver

[0037] 10. Intermittent open solder joint contact at TXDL or RXDL of the transceiver

[0038] 11. When using common mode chokes, there may also be errors associated with them (eg, related to soldering points).

[0039] The typical solution using a larger capacitor 108 has disadvantages. The bit rate is limited to 125kbit / s. The solution requires an external 511Ω at the termination end (connected between the RtL pin of the CAN transceiver and CANL, and between the RtH pin of the CAN transceiver and CANH). This solution does not allow a "standardized" CAN transceiver pinout. The internal switches on the RtH and RtL pins need to be implemented with high voltage transistors, so that the typical solution will require a larger silicon wafer area for the CAN transceiver. It should be noted that the CAN transceiver is part of the node 104-1 ... 104-N. The CAN transceiver (not shown) is connected between the twisted pair 106 of the CAN protocol controller (not shown) and the CAN bus 100. CAN transceivers and CAN protocol controllers are well known in the art.

[0040] Figure 3 A CAN transceiver 300 is shown. The CAN transceiver 300 includes features that provide redundancy with respect to failures of the CANL and CANH wires or failures in the microcontroller or communication failures between the microcontroller and the transceiver 300 or other bus conditions that could potentially cause or indicate an error condition.

[0041] The inventor's U.S. application Ser. No. 16 / 693,022, filed on Nov. 22, 2019, entitled "CAN communication with disconnected cable," describes regulating bus split voltage, which is incorporated herein by reference in its entirety. The inventor's U.S. application Ser. No. 16 / 509,304, filed on Jul. 11, 2019, entitled "communication between a transceiver and a microcontroller," describes bidirectional communication between a microcontroller and a transceiver, which is incorporated herein by reference in its entirety.

[0042] The transceiver 300 includes two transmitter pins TX1, TX2 and two receiver pins RX1, RX2. In some examples, two microcontrollers or ECUs can be coupled to the transceiver 300 to provide redundancy in the event of a microcontroller failure. For example, TX1 can be connected to microcontroller 1 and TX2 can be connected to microcontroller 2. The two microcontrollers can be coupled to two different subsystems (e.g., a brake control system) to provide redundancy. This redundancy provides better safety that is desired in modern vehicles, especially with autonomous driving features. In some embodiments, the transceiver 300 can also support more than two microcontrollers.

[0043] The transceiver 300 includes a system monitor 302 configured to monitor TX1, TX2, RX1, and RX2 lines. For example, the system monitor 302 also monitors the CANL line and the CANH line to monitor the voltage. The system monitor 302 can also monitor the temperature, safety, and security-related events on the CAN bus 100. For example, the system monitor 302 can check whether the communication on the transmitter and receiver lines complies with the CAN protocol. For example, the system monitor 302 can check the voltage level, and if the voltage level exceeds a predetermined threshold, switch to the second set of transmitter lines and receiver lines. The transceiver 300 may include an ERR pin coupled to the system monitor 302 to provide an error signal to an external entity such as a microcontroller (not shown) coupled to the transceiver 300. The TX1 and TX2 lines can be coupled to a line selector (Mux TX) 304. For example, the system monitor 302 can continuously monitor the TX1 line, and if it detects a communication failure on TX1, the system monitor 302 can select the TX2 line. In some examples, the system monitor 302 can also select the RX2 line while selecting TX2. Transmission failures can be detected by monitoring the voltage level on TX1 and verifying the data frame on TX1. When switching to TX2 occurs, the ERR signal can be activated so that the external (i.e., external to the transceiver 300) monitoring system can, for example, notify the operator of the vehicle. In some examples, for safety reasons, the driving control system can turn the vehicle to a safe position. The redundancy feature provided by the transceiver 300 will continue to ensure normal or controllable operation until the redundant component also fails. However, in some examples, the time interval between the failure of the first microcontroller and the second microcontroller may be sufficient to turn the vehicle to safety. A receiver line selector (Mux RX) 306 is included to switch between the first microcontroller and the second microcontroller. Mux TX 304 and Mux RX 306 can be operated synchronously by the system monitor 302, that is, if TX2 is selected, RX2 is also selected. In some embodiments, the receiver line selector 306 and the transmitter line selector 304 may be implemented using toggle switches that may be operated using the same drive signal to toggle both switches simultaneously to switch from microcontroller 1 to microcontroller 2 .

[0044] The transceiver 300 includes a transmitter and a receiver 312 coupled to the CANL line and the CANH line. For simplicity, the transmitter and the receiver are shown in FIG. Figure 2. In some examples, the transmitter and receiver can be manufactured separately on the chip. System monitor 302 can be coupled with transmitter / receiver 312 to monitor communication and also monitor the voltage level at CANH, CANL to identify any disconnection of error conditions in the reception or transmission of data. Voltage regulating circuit 310 can be included to generate Vsplit voltage based on monitoring of CANH line and CANL line to ensure that there is at least temporarily some degraded communication in the case of open circuit of CANL wire or CANH wire. Transmission enabling circuit 308 can be provided to reliably stop transmission when safety conditions require.

[0045] Figure 4 A sample implementation scheme of a voltage regulating circuit 310 for generating a bias voltage to overcome an error condition on CANH or CANL is shown. The bias voltage is applied to capacitor 108. Voltage regulating circuit 310 includes resistor R1a and resistor R1b coupled to CANH. Resistor R1a and resistor R1b are coupled to comparator A1. An optional level shifter 404 may be included to change the voltage domain of the voltage at the output of comparator A1. Voltage regulating circuit 310 additionally includes resistors R2b and R2a coupled to comparator A2. An optional level shifter 406 may be included to change the voltage domain of the voltage at the output of comparator A2. A configurable voltage source 402 may be included to adjust the voltage at the end of capacitor 108.

[0046] Resistors R2b and R1b allow current sensing in the CANL branch and the CANH branch, respectively. The sensing current is converted into voltage via differential amplifiers A1 and A2. When the sensing current in the CANH branch (detected via comparator A1) is zero but the sensing current in the CANL branch (detected via comparator A2) is not zero, an open circuit CANH connection is detected, and in one example, a configurable voltage source 402 is configured to generate 4V. Similarly, when the sensing current in the CANL branch (detected via comparator A2) is zero but the sensing current in the CANH branch (detected via comparator A1) is not zero, an open circuit CANL connection is detected, and in one example, a configurable voltage source 402 is configured to generate 1V. In other cases, the configurable voltage source 402 is biased to 2.5V (Vcc / 2, equal to half of the power supply voltage). A controller 408 is included to send a control signal to the configurable voltage source 402 based on the sensing current in the CANH branch and the CANL branch as described above.

[0047] For the configurable voltage source 402, various implementations are possible. Figure 5 and Figure 6 Two such example implementations are shown. Figure 5A configurable voltage source 402 using a resistor divider is shown. When both switch S1 and switch S2 are open, the separation voltage VSplit (which is applied to terminal 102 of capacitor 108) is set to 2.5V (Vcc divided by two). When switch S1 is closed (and switch S2 is open), the separation voltage VSplit is set to 4V, and when switch S2 is closed (and switch S1 is open), the separation voltage VSplit is set to 1V. Switches S1 and S2 are opened or closed based on a control signal from a controller 408.

[0048] Figure 6 A configurable voltage source 402 in another embodiment 402A is shown. In this embodiment, the configurable voltage source 402A includes a comparator 410 coupled to a reference voltage Vref, and the comparator 410 is configured to drive a transistor M1. Switches S1 and S2 are controlled by a control signal from a controller 408. The configurable voltage source 402A is based on a linear voltage regulator operation, where the voltage feedback ladder is configured in different ways depending on the desired nominal output voltage. When both switches S1 and S2 are open, the split voltage (VSplit) is set to 1V. When switch S1 is closed and switch S2 is open, VSplit is set to 4V. When switch S2 is closed and switch S1 is open, Vsplit can also be set to 2.5V. It should be noted that the reference voltage (Vref, which is equal to 0.6V in the example embodiment) is a well-known bandgap voltage reference, but can alternatively be implemented by a resistor divider connected to Vcc so that the output voltage will also track the supply voltage Vcc.

[0049] Figure 7 An example implementation of an enabling circuit 308 is shown. An entity external to the transceiver 300 uses the TXEN signal to enable or disable transmission via the transceiver 300. During some safety events, it is important to reliably stop the transmission of signals from the transceiver 300 to the CAN bus 100. The example implementation uses a set of CANH switches 316 and a set of CANL switches 318. A set of switches 316, 318 may include multiple individual switches in series. In some examples, (for example) due to a switch failure, using only one switch may not completely stop the transmission.

[0050] Figure 8 Transceiver 300A is shown. Obviously, not all components are Figure 8, so as not to confuse the present disclosure. Transceiver 300A includes transistors T1, T2, T3, T4 and diodes D1, D2, D3, D4 coupled to a first slope controller 320 and a second slope controller 322. Slope controller and associated circuit arrangements including transistors and diodes are used to provide CANL, CANH differential signals. System monitor 302 can be coupled with slope control circuit arrangements at junctions 324 and 326. If system monitor 302 detects an open circuit CANH or an open circuit CANL, system monitor 302 can provide a voltage at junctions 324 or 326 so that even one wire has enough voltage swing to enable communication via one wire. In some examples, a voltage swing is provided to CANL / CANH and a bias voltage Vsplit is provided to capacitor 108, as previously described.

[0051] Fig. 9 The CAN bus 100 is shown using a transceiver 300. As shown, the transceiver 300 includes two RX lines and two TX lines to couple with two ECUs or microcontrollers to provide redundancy.

[0052] Some or all of these embodiments may be combined, some may be omitted entirely, and additional process steps may be added while still achieving the products described herein.Thus, the subject matter described herein may be embodied in many different variations, and all such variations are contemplated to be within the scope of the claims.

[0053] Although one or more embodiments have been described by way of example and according to specific embodiments, it should be understood that one or more embodiments are not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements that will be obvious to those skilled in the art. Therefore, the scope of the appended claims should be given the broadest interpretation so as to cover all such modifications and similar arrangements.

[0054] Unless otherwise indicated herein or clearly contradicted by the context, the use of the terms "a / an" and "said" and similar indicators in the context of describing elements (especially in the context of the above claims) should be understood to cover the singular and the plural. Unless otherwise indicated herein, the description of the value range herein is intended only to serve as a shorthand method for individually referring to each individual value belonging to the range, and each individual value is incorporated into this specification as if it were individually described herein. In addition, the above description is for illustrative purposes only, not for limiting purposes, because the scope of protection sought is defined by the claims set forth below and any equivalents thereof. Unless otherwise required, the use of any and all examples or exemplary language (e.g., "for example") provided herein is intended only to better illustrate the subject matter, without limiting the scope of the subject matter. The use of the term "based on" and other similar phrases indicates the conditions for producing the results in the attached claims and written descriptions, and is not intended to exclude other conditions for producing the results. Any language in this specification should not be understood as indicating any non-claimed elements necessary for practicing the claimed invention.

[0055] Preferred embodiments known to the inventor for practicing the claimed subject matter are described herein. Of course, after reading the above description, variations of those preferred embodiments will be clear to those skilled in the art. The inventor expects that such variations will be adopted by those skilled in the art in due course, and the inventor intends to practice the claimed subject matter of the present invention in other ways than those specifically described herein. Therefore, the claimed subject matter includes all variations and equivalents of the subject matter recited in the attached claims as permitted by applicable law. In addition, unless otherwise indicated herein or otherwise clearly contradictory to the context, any combination of the above-mentioned elements with all possible variations thereof is encompassed.

Claims

1. A transceiver, characterized in that: include: a first receiver line, a first transmitter line, a second receiver line, and a second transmitter line, wherein the first receiver line and the second receiver line are coupled to a receiver line selector, and the first transmitter line and the second transmitter line are coupled to a transmitter line selector; a system monitor configured to monitor a controller area network (CAN) bus and the first transmitter line, and select the second transmitter line and the second receiver line if an error condition is detected by said monitoring of the first transmitter line; as well as A bias voltage generator generates a bias voltage for a termination capacitor of the CAN bus, wherein the bias voltage generator is activated by the system monitor when an error condition is detected in the CAN bus.

2. The transceiver according to claim 1, characterized in that: The system monitor is additionally configured to monitor the first receiver line for the error condition and select the second transmitter line and the second receiver line via the receiver line selector and the transmitter line selector.

3. The transceiver according to claim 1, characterized in that: The receiver line selector and the transmitter line selector are configured to operate simultaneously.

4. The transceiver according to claim 1, characterized in that: Additionally included is an enabling circuit configured to disable communications to the CAN bus, wherein the enabling circuit includes two series switches that operate simultaneously to disconnect power to the CANL pin.

5. The transceiver according to claim 1, characterized in that: In addition, a voltage regulating circuit is configured to generate a bias voltage for a terminated end of the CAN bus when an open wire in the CAN bus is detected to allow communication with the CAN bus using one wire.

6. The transceiver according to claim 1, characterized in that: The system monitor includes a CAN bus error detector including a first comparator, a first resistor and a second resistor, wherein the first comparator is connected across the second resistor and an end of the first resistor is connected to a CANH pin.

7. The transceiver according to claim 1, characterized in that: The system monitor includes a CAN bus error detector including a first comparator, a first resistor and a second resistor, wherein the comparator is connected across the second resistor and an end of the first resistor is connected to a CANL pin.

8. The transceiver according to claim 6, characterized in that: The CAN bus error detector includes a configurable voltage source including a first set of resistors coupled to a first switch and a second set of resistors coupled to a second switch.

9. The transceiver according to claim 8, characterized in that: The first switch and the second switch are configured to bypass one or more resistors of the plurality of resistors based on a control signal.

10. The transceiver according to claim 1, characterized in that The bias voltage is either 1V or 4V depending on the error condition.

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