Line termination circuit with configurable termination resistance

Abstract

According to an example aspect of the present invention, there is provided a line termination circuit for a signal line pair of a Controller Area Network, CAN, bus The line termination circuit comprises a resistor assembly (21) and a semiconductor switch unit (22) connected in serie between two lines of the line pair, wherein the semiconductor switch unit (22) a comprises at least one field-effect transistor, FET, configured to be controlled to a conducting state or to a non-conducting state with a gate drive voltage at its gate, a switch driver circuit (3) configured to generate the gate drive voltage in response to a driver activation voltage, and a control circuit (4) comprising a termination control input, wherein the control circuit (4) is configured to generate the driver activation voltage at least partially based on a termination control command at the termination control input, the gate drive voltage having a greater voltage swing than the driver activation voltage.

Description

LINE TERMINATION CIRCUIT WITH CONFIGURABLE TERMINATIONRESISTANCEFIELD

[0001] The present disclosure relates to communication buses in which signals are sent and received on a line pair of two complementary signal lines, and particularly to configurable line termination of CAN buses.BACKGROUND

[0002] Electrical systems in road vehicles and non-road mobile machinery are getting more intricate in each generation. More sophisticated functions require more controllability which means more electronic control units. In the context of the present disclosure, the term “electronic control unit”, or “ECU”, refers to an embedded system that is typically used in automotive electronics, as well as non-road mobile machinery, NRMM, that rely on batteries for electrical power. ECUs typically comprise at least one microcontroller unit, MCU, that is used to control one or more of the electrical systems or subsystems in a car or other machinery. A MCU typically comprises a processor, memory and a set of programmable peripherals and input / output interfaces, and can be programmed to perform a desired function or functions.

[0003] ECUs typically need reliable and robust communication networks and protocols for their communication. Controller Area Network, CAN, is an example of such a communication protocol. CAN utilizes a differential bus topology that comprises a signal line pair of two complementary wires called CAN High (CANH) and CAN Low (CANL). There are two logical states for the bus: a recessive state and a dominant state. During the recessive state, no differential voltage is driven across the wires and a voltage difference between CANH and CANL is approximately zero. The recessive state on the bus can take place when a recessive bit is transmitted during a message, or when the bus is idling. When a dominant bit is transmitted, a dominant bus state is activated by driving a differential voltage between CANH and CANL. If both bits, i.e., a dominant bit and a recessive bit, are transmitted simultaneously by different ECUs, the dominant bit is resulted on the bus.

[0004] A CAN bus requires termination resistance to ensure network integrity and proper data transmission. This means that termination resistors may have to be placed at the physical ends of the bus. Termination minimizes signals from reflecting off the end of a transmission line. Reflections at the ends of an unterminated transmission lines cause distortion, which can produce ambiguous digital signal levels and incorrect operation of digital systems. Further, the termination resistances dampen differential-mode noise caused by inductive noise coupling. It is also worth noting that the termination resistor plays a role in returning the CAN bus state back to recessive after a dominant bit. Without termination resistors, the differential voltage on the bus decays slower, and the recessive state might not be achieved before sampling of the bit.

[0005] Generally, there are two ways to achieve line termination for nodes of the CAN bus: either by placing external resistors between the signal lines, or by assembling the resistors inside the nodes. A node, such as ECU, with integrated termination resistors can only be used at the physical ends of the bus. This sets an inconvenience to ECU designers because many assembly variants or products are needed: some with and some without the termination resistors. This also requires planning from the users who design the systems the ECU will be a part of: they need to know which units will be located at the end of the CAN bus. Externally placed resistors, on the other hand, require custom cables, which lead to extra work and cost.

[0006] Configurable termination resistances enable the control unit to be used either at the ends of the bus or somewhere in between. A user of an ECU can configure the termination on or off depending on where the unit is located on the bus which makes the design of the network easier. However, the existing implementations may not be able to fulfil all operating requirements, particularly in more demanding fields of application, such as in the NRMM field. These requirements may relate to expected component lifespan, temperature, vibration and shock tolerance as well as power consumption, for example. Some existing implementations even fall short regarding requirements set in CAN standards, such as ISO 11898-2.

[0007] For example, one known approach for a configurable termination to use an optocoupler to switch a termination resistor on or off. The main advantage of using optical isolators is a galvanic isolation between the CAN bus and the control logic, which prevents electrical noise to coupling on the bus from a control circuit controlling the termination andoperates with a wide common-mode voltage range of the bus. However, optocouplers have some major disadvantages. For example, optocouplers typically have poor temperature tolerance. Optocouplers also typically require a relatively large current to reliably turn on. Additionally, the behaviour of light emitting diodes in optocouplers is highly temperature dependent. Their lifetime decreases and required drive current increases in high temperatures.

[0008] Another approach is to use a relay for switching the termination resistor on or off. With a relay, a galvanic isolation between the CAN bus and the control logic can be achieved. However, relays have poor vibration and shock tolerance, they are heavy and physically large components, require significant power for operating, and their service life is limited.SUMMARY

[0009] The present disclosure presents a line termination circuit that alleviates the above-discussed problems. According to some aspects, there is provided the subject-matter of the independent claims. Some embodiments are defined in the dependent claims. The scope of protection sought for various embodiments of the invention is set out by the independent claims. The embodiments, examples and features, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various embodiments of the invention.

[0010] According to a first aspect of the present disclosure, there is provided a line termination circuit for a signal line pair of a Controller Area Network, CAN, bus, the line termination circuit. The circuit comprises a resistor assembly and a semiconductor switch unit (or, simply, a switch unit) connected in series between two lines of the line pair, a switch driver circuit (or, simply, a switch driver) for controlling the semiconductor switch unit, and a control circuit for controlling the switch driver circuit. The semiconductor switch unit comprises at least one field-effect transistor, FET, that is configured to be controlled to a conducting state or to a non-conducting state with a gate drive voltage at its gate. The switch driver circuit is configured to generate the gate drive voltage in response to a driver activation voltage. The control circuit comprises a termination control input, and is configured to generate the driver activation voltage at least partially based on a termination control command at the termination control input. The gate drive voltage has a greater voltage swing than the driver activation voltage.

[0011] With the line termination circuit according to the present disclosure, a large common-mode voltage tolerance can be achieved while maintaining a low power consumption of the circuit. At the same time, the line termination circuit has a large operating temperature range and a good vibration and shock tolerance. Further, the powerconsumption of the circuit can be maintained at a very low level. The line termination circuit can be implemented without fast-aging components included, which increases the lifespan and robustness of the circuit.

[0012] Traditionally CAN networks stay unchanged in road vehicles or non-road mobile machinery throughout their lifespan. However, configurable termination allows the network to be changed. For example, nodes can be added or removed without any hardware modification to the termination. If used as a service spare part, an ECU with a configurable termination resistance can be installed at the end of a CAN bus or in between of the bus ends without need to have separate part versions for both install locations due to varied internal termination resistance assembly.

[0013] A line termination circuit according to the present disclosure can be provided with a memory unit that stores the set state of the configurable termination resistance. In this manner, the line termination circuit does not require a constant control signal. This is advantageous in applications with different operating modes, such as a sleep mode.BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIGURE 1 illustrates a simplified diagram of elements used to form a line termination circuit according to the present disclosure, connected to a CAN bus;

[0015] FIGURE 2 shows an example implementation of elements of a line termination circuit according to the present disclosure;

[0016] FIGURE 3 shows an example of a control circuit of a line termination circuit according to the present disclosure;

[0017] FIGURE 4 illustrates a simplified example implementation of a configurable termination resistance according to the present disclosure where its semiconductor switch unit is in the form of a bidirectional switch; and

[0018] FIGURE 5 illustrates a configurable termination resistance where its resistor assembly is formed by two halves.EMBODIMENTS

[0019] The present disclosure describes a line termination circuit for a signal line pair of a Controller Area Network, CAN, bus. In the context of the present disclosure, the term “line termination circuit” is intended to be understood as an electrical circuitry comprising a combination of electrical components and conductor traces / wires therebetween, the combination being configured to implement the functionality of line termination. As will be shown below, a line termination circuit according to the present disclosure can be divided into several subcircuits or elements, each having their own function within the context of the line termination.

[0020] CAN buses are often used in applications where control electronics are battery- powered, which include light and heavy-duty road vehicles, non-road mobile machinery, and other kinds of heavy machinery. Electrical control units, ECUs, in this kind of applications typically use CAN buses for their communications. These applications commonly use either 12 V or 24 V batteries for powering electrical equipment. Road vehicles, like ICE (internal combustion engine) cars, commonly use 12 V system voltage, whereas larger vehicles, like trucks, busses and other heavy-duty machinery use 24 V due to higher power consumption and longer cables. The operating environment, particularly in heavy duty road vehicles and in NRMM, may set tough physical and electrical requirements for an implementation of the CAN bus.

[0021] The differential bus topology of a CAN bus allows a common-mode voltage to appear on the bus without impairing the communication. This common-mode voltage that is different than the nominal level can appear, for example, if there is a difference in the ground potentials between nodes due to poor grounding, or if the bus is short-circuited to some voltage level, like the supply voltage line in a road vehicle. Requirements set for a CAN bus may also depend on the version of CAN bus being used. For example, the nominal voltage level for the recessive state, according to J1939 and ISO 11783 standards, is 2.5V, which means that the bus is actively biased to this voltage level. However, in the newest versions of ISO 11898-2, bus biasing is optional in a low-power mode, and the nominal recessive bus level without it is 0V. The maximum and minimum voltage levels of each wire in respect to ground, while proper operation is still guaranteed, are specified differently across these standards. Older standards required a common-mode voltage range from -2V to +7V, and the newest versions of ISO 11898-2 from -12V to +12V.

[0022] A line termination circuit according to the present disclosure enables configurability of a termination resistance in a CAN bus. An ECU with one or more CAN buses may be provided with the line termination circuit so that the ECU can be easily configured to have a termination resistance present or absent in its one or more CAN buses. Further, a line termination circuit according to the present disclosure can be easily adapted to different requirements.

[0023] A line termination circuit according to the present disclosure comprises a configurable termination resistance connected between two lines of the line pair of the CAN bus, a switch driver circuit configured to set up the configurable termination resistance, and a control circuit configured to control the switch driver circuit. FIGURE 1 shows a simplified diagram of elements used to form the line termination circuit connected to a CAN bus.

[0024] In FIGURE 1, the CAN bus has two signal lines CANH and CANL, marked with reference numbers 11 and 12, respectively. The signal lines 11 and 12 are connected to a CAN transceiver 1. In some embodiments, the CAN transceiver 1 may be connected to the signal lines via a common-mode choke that filters out high-frequency noise. Further, the CAN bus may also be provided with ESD protection. In FIGURE 1, a common-mode choke 13 and an ESD protection unit 14 are shown with dashed lines.

[0025] The line termination circuit in FIGURE 1 comprises a configurable termination resistance 2, a switch driver circuit 3, and a control circuit 4. The configurable termination resistance 2 comprises a resistor assembly 21 and a semiconductor switch unit 22 connected in series between the signal lines 11 and 12. Nominal characteristic impedance of the line pair of the CAN bus is 120Q. Thus, a matching termination resistance value of 120Q at each physical end of the CAN bus may be required to ensure signal integrity. In FIGURE 1, the resistor assembly 21 represents this resistance. While presented as a single resistor in FIGURE 1, the resistor assembly 21 may also be formed by a plurality of resistors in series and / or in parallel. Also, in the context of present disclosure, a resistor assembly may be formed by two separate halves with the semiconductor switch unit 22 therebetween.

[0026] The semiconductor switch unit 22 a comprises at least one field-effect transistor, FET, configured to be controlled to a conducting state or to a non-conducting state with a gate drive voltage Vdrv at its gate. In this context, the term “conducting state” refers to the saturation mode of the FET, and the term “non-conducting state” refers to the cut-off mode. A metal-oxide-semiconductor field-effect transistor, MOSFET, is an example of aFET. MOSFETs provide cheap and versatile options for being used as a semiconductor switch. Further, MOSFETs (and FETs in general) are driven with a voltage instead of a current. The semiconductor switch unit 22 can be used to connect the resistor assembly 21 between the signal lines 11 and 12, or to disconnect the connection. Thus, with the configurable termination resistance 120, a termination resistance of a node in the CAN bus can be selected to be present or absent between the signal lines 11 and 12. In other words, the configurable termination resistance may be considered to have two states: an “on” state where the termination is present and an “off’ state where the termination resistance is not present.

[0027] In FIGURE 1, the switch driver circuit 3 is configured to generate the gate drive voltage Vdrv in response to a driver activation voltage vact. The control circuit 4 comprises a termination control input Ctrl, and the control circuit is configured to generate the driver activation voltage Vdr at least partially based on a termination control command at the termination control input Ctrl. The termination control input Ctrl may comprise one or more signal lines. In this context, the phrase “at least partially” is intended to mean that the generation of the driver activation voltage in response to the termination control command, but, in some embodiments, the generation of the driver activation voltage may also be responsive to other signals.

[0028] In the context of the present disclosure, a termination control command may be in the form of a predetermined level of a parameter (e.g., voltage) provided on the one or more signal lines. For example, a termination control command may be in the form of a continuous signal in the form of one or more voltage levels, each provided on a different signal line of the one or more signal lines. Another example of a termination control command is a voltage pulse or pulses on the one or more signal lines. Further, the termination control command may be a combination of voltage levels and pulses. The termination control command may originate from an MCU of an ECU on which the line termination circuit has been implemented, for example.

[0029] In a line termination circuit according to the present disclosure, the gate drive voltage Vdrv has a greater voltage swing (i.e., voltage range) than the driver activation voltage Vact- In this context, the phrase “greater voltage swing” is intended to mean that when the switch driver circuit 3 generates the gate drive voltage Vdr , the gate drive voltage Vdr reaches a voltage potential not reached by the driver activation voltage vact. For example, inembodiments where the semiconductor switch unit 22 is controlled to the conducting state with a positive voltage, the gate drive voltage Vdrv is higher than the driver activation voltage Vact- Alternatively, in embodiments where the semiconductor switch unit 22 is controlled to the conducting state with a negative voltage, the gate drive voltage Vdrv is lower (more negative) than the driver activation voltage vact.

[0030] By having a large voltage range for the gate drive voltage Vdrv, the switch driver 3 is more reliably able to control the semiconductor switch unit 22 to the desired state, i.e., to the conducting state or the non-conducting state, and, thus, a common-mode voltage tolerance of the line termination circuit is improved. In this context, the term “commonmode voltage tolerance” refers to a guaranteed ability to set the configurable termination resistance to a desired state within a range of common-mode voltages the signal line of the CAN bus may have. In some applications, the common-mode voltage range may be from less than -10V to more than +10V, for example. However, a line termination circuit according to the present disclosure is not limited only to said range. The line termination circuit can be easily scaled to withstand even more extensive common-mode voltage ranges, such as from less than -12V to more than +12V, from less than -15V to more than +15V, or even more. More restricted ranges than the -10V to +10V can of course also be used.

[0031] Next, various elements and functional aspects of a line termination circuit according to the present disclosure are discussed in more detail in reference to FIGURE 2 and other figures. FIGURE 2 shows an example implementation of elements of a line termination circuit according to the present disclosure. The implementation presented in FIGURE 2 may be used in the embodiment of FIGURE 1, for example.

[0032] In FIGURE 2, a configurable termination resistance 2, a switch driver circuit 3, and a control circuit 4 are shown. Only the two signal lines CANH 11 and CANL 12 of the CAN bus are shown, other parts of the CAN bus, such as the CAN transceiver, have been omitted. The resistor assembly 21 and the semiconductor switch unit 22 of the configurable termination resistance 2 connected between the CANH 11 and CANL 12.

[0033] One functional aspect of a control circuit in a line termination circuit according to the present disclosure is ability to operate under different operating modes of its parent unit. In the context of the present disclosure, the term “parent unit” refers a larger unit in which the line termination circuit has been implemented. For example, the line termination circuit may be implemented in a parent unit that is in the form of an ECU that has to be ableto go to a low-power mode, such as a sleep mode. In a low power mode, the main power supplies of the parent unit may be powered off to reduce current consumption. Thus, the parent unit (e.g., an ECU or its MCUs) may not be able to provide a continuous termination control command holding the configurable termination resistance in a desired state. However, it may be preferable to be able to maintain the state of the line termination regardless of the mode the parent unit.

[0034] To ensure proper operation under different operating modes of the parent unit, the control circuit may comprise a memory unit. In the context of the line termination circuit according to the present disclosure, the term “memory unit” refers to a component or a portion of a component implementing a functionality of storing a representation of a state indicated by an input and reproducing the stored representation at an output. A simple example of this representation is one stored bit of digital logic. The memory unit may be implemented in the form of circuit formed out of one or more discrete logic gates, a simple latch (e.g., D-latch or SR-latch) or a flip-flop on a discrete IC, for example. Other implementations of memory unit can also be used.

[0035] In a line termination circuit according to the present disclosure, the memory unit may be configured to store a representation of a state of the configurable termination resistance based on a termination control command and reproduce the stored representation at its output. The driver activation voltage vact may then be generated at least partially based on the stored representation at the output of the memory unit. The representation of a state stored by the memory unit may represent the state of the configurable termination resistance (e.g., “on” or “off’). In Figure 2, the control circuit 4 comprises a memory unit 41. The driver activation voltage vact is generated at least partially based on the stored representation at the output of the memory unit 41. For example, in some embodiments, an output voltage at the output of the memory unit 41 is used as the driver activation voltage vact.

[0036] In some embodiments, there is a single termination control command for toggling the state of the configurable termination resistance 2 between the “on” state and the “off’ state. Thus, depending on the current state of the configurable termination resistance 2, the same command may be a termination-activating command or a terminationdeactivating command. For example, the termination control command may be the form of a voltage pulse and the memory unit 41 may be configured to change its output in response to the voltage pulse at its input. Thus, the voltage at the output of the memory unit changes41 from a low voltage level to a high voltage level when the termination control command is received, and back from the high voltage level to the low voltage level when the termination control command is received again. In the context of the termination control command, the term “voltage pulse” is intended to be understood as a change of state of a binary signal from one state to another, and then back to the original state, e.g., from low voltage level to high voltage level and then back to the low voltage level again. The duration of the pulse is configured to be sufficient to set the memory unit to a desired state. The terms “low voltage level” and “high voltage level”, or simply “low” and “high”, refer to the two states of the binary signal produced by the memory unit.

[0037] As an alternative to the embodiment with a single termination control command, there may be different commands for turning the configurable termination resistance on and off. For example, there may be a termination-activating command for turning the configurable termination resistance on, and a termination-deactivating command for turning the configurable termination resistance off. For example, the control circuit may be configured to recognize two different termination control commands: a first command for setting the configurable termination resistance on and a second command for setting the termination resistance off. The memory unit may be configured to then store a representation of the state of the configurable termination resistance based on the recognized command. In this approach, it is not necessary to keep track on the current state of the configurable termination resistance.

[0038] An advantage of having the memory unit 41 is that the set state (i.e., connected or disconnected) of the configurable termination resistance 2 can be maintained even when a termination control command cannot be continuously provided. As explained earlier, it may be desirable to set a controller (e.g., an MCU of an ECU, not shown in FIGURE 2) to its sleep state. The memory unit 41 allows the controller to be set to the sleep mode without affecting the operation of the line termination. After the memory unit 41 has received a termination control command from the controller, the memory unit 41 maintains its output state as configured until the memory unit itself is powered off or another termination control command is received. To achieve this, the memory unit 41 may be supplied from a power supply that is active even when the parent unit (e.g., an ECU) is in a low-power mode, so that the memory unit 41 is supplied regardless of operating mode of the parent unit. In Figure 2, such a power supply is shown as Vstandby.

[0039] The memory unit 41 may be configured such that its output is in a predefined state when the unit is initially powered on. The control circuit 4 and its memory unit 41 may be configured to have a default state. In a first variant, the default state is on, where the configurable termination resistance 2 is switched on as soon as supply voltage Vstandby is connected to the control circuit 4, even if a termination-activating control command has not yet been received. Alternatively, in a second variant, the default state is off, and the configurable termination resistance 2 is off when supply voltage is switched on and are turned on only if a termination-activating control command is received at the input Ctrl of the control circuit 4.

[0040] FIGURE 3 shows an example of a control circuit of a line termination circuit according to the present disclosure. The example may represent an implementation of the control circuit 4 of FIGURE 1 and / or FIGURE 2, for example. In FIGURE 3, the control circuit 4 comprises a memory unit 41, a power supply 42, and an optional pull-down resistor 43. The memory unit 41 has an input Ctrl to which the termination control command is produced. The termination control command may be generated by an MCU of the parent unit (e.g., ECU).

[0041] In FIGURE 3, the power supply 42 (in the form of a voltage regulator) provides an internal backup supply voltage Vstandby for the control circuit 4. The power supply 42 itself is supplied from a power supply Vbat that is always available (i.e., it is not affected by the sleep mode). Thus, the internal backup supply voltage Vstandby is always on, regardless of the mode of the parent unit. Because the memory unit 41 uses this supply voltage Vstandby, it is able to hold the selected state of termination even when the parent unit itself goes into a sleep mode and its main power supplies are powered off. The voltage level of the supply voltage Vstandby may be selected such that it is corresponds voltage levels of typical logic circuits. The supply voltage Vstandby may be +5V, for example. In FIGURE3, voltage levels of the voltage driver activation voltage vact outputted by the memory unit 41 are defined by the supply voltage Vstandby. In order to minimize the power consumption of the control circuit 4, it may be desirable use a low-power power supply for generating a supply voltage for the components in the control circuit 34. For example, the power supply 42 may be a low-power, low-dropout, LDO, regulator that has very low quiescent current.

[0042] While the above examples describe the line termination circuits with memory units in their control circuits, a line termination circuit according to the present disclosure may also be implemented without a memory.

[0043] Another functional aspect of the line termination circuit according to the present disclosure is improving common-mode voltage tolerance range of the termination of the CAN bus. To achieve this, the gate drive voltage Vdrv generated by the switch driver circuit 3 in FIGURE 2 has a greater voltage swing than the driver activation voltage vact generated in the control circuit unit 4. For example, as shown in FIGURE 2, the switch driver circuit 3 may comprise a first voltage source 31 (shown only as a supply voltage symbol) configured to generate a first voltage. A power supply 31 of the parent unit act as the first voltage source, and the supply voltage Vbat generated by this power supply 31 may be used as the first voltage, for example. The first voltage may be used as the gate drive voltage Vdrv. In this manner, a common-mode voltage tolerance range of at least -2V to +7V, at least - 10V to +10V, at least -12V to +12V, at least -15V to +15V or even more can be achieved, depending on the voltage range of the supply voltage Vbat. Of course, leakage currents are typically proportional to voltages used, and thus it may not be desirable set an unnecessarily large tolerance range.

[0044] It may be desirable to be able to use different supply voltages. For example, in different applications, the same parent unit may be provided with different supply voltages. In some cases, the supply voltage Vbat of the parent unit may not be sufficient to drive gate drive voltage Vdrv to the desired state. Some applications allow lower supply voltages than needed for fulfilling common-mode voltage tolerance requirements of CAN bus.

[0045] Also, it may be desirable to provide further security for the generation of the gate drive voltage Vdrv- In some applications, ECUs, and their line termination, are required to be able to operate even under very harsh conditions. For example, a worst-case scenario in some applications may present a situation where a combination of a very low ambient temperature (e.g., -40°C), a highest allowed common-mode voltage on CAN bus, and lowest allowed supply voltage level (e.g., 4,5 V during cold cranking) result in a situation where the first voltage is not sufficient to drive the semiconductor switch unit 22 to the desired state.

[0046] To ensure that that the termination resistance can be kept in a desired state regardless of the operating conditions, the switch driver circuit 3 may comprise a secondpower source, as shown in FIGURE 2. In FIGURE 2, the second power source is in the form of a charge pump 32 configured to convert a supply input voltage Vstandby into a second voltage in response to the driver activation voltage vact- In this context, the term “charge pump” refers to a switched-mode DC-DC converter that uses energy stored in its capacitors to create output voltage that is higher than input voltage. There are many different variations of charge pump topologies, one example of such topology being Dickson’s charge pump. In some embodiments, a higher output voltage can be generated by implementing additional stages to the charge pump.

[0047] In some embodiments, the same supply voltage used to supply the control circuit 4 may also be used to supply voltage for the charge pump 32, e.g., as shown in FIGURE 2. In some embodiments, the charge pump 32 is supplied directly from the driver activation voltage vact.

[0048] The charge pump 32 in FIGURE 2 may be configured such that it is be able to create a second voltage that is the sum of the voltage on CANL and the threshold voltage of the termination switch and some marginal. The maximum allowed common-mode voltage on the CAN bus depends on the standard being applied. For example, if compliance to ISO 11898-2 for CAN interfaces is wanted, the charge pump may be configured to generate around 15V to be used as the gate drive voltage Vdr . To improve power-efficiency of the charge pump, Schottky diodes with lowest possible forward voltage and minimal reverse leakage current may be used. Further, low-power implementation of a clock signal may be used for the charge pump. For example, the clock signal may be implemented with CMOS 555 timer IC.

[0049] As shown in FIGURE 2, the first voltage source 31 and second voltage source 32 may be used together to generate the gate drive voltage Vdr . For example, in FIGURE 2, the switch driver circuit 3 further comprises a voltage selector 33 configured to select the higher voltage from the first and second voltage and use the selected voltage as the gate drive voltage Vdrv. The voltage selector 33 may be created by using forward-biased diodes (not shown in FIGURE 2) after outputs of the first power supply 31 and the second power supply 32, for example. The diodes connect to a common output, thus forming a diode voltage source selector. The voltage at this common output corresponds to highest output voltage of the two supplies 31 and 32.

[0050] In FIGURE 2, the switch driver circuit 3 is configured to generate the gate drive voltage Vdrv in response to a driver activation voltage vact- For example, in some embodiments, the driver activation voltage vact controls two switches. In FIGURE 2, the supply voltage Vbat of the first power source 31 is connected to the voltage selector 33 via a switch 34. The other supply voltage Vstandby is connected to the charge pump 32 via another switch 35 in FIGURE 2. When the driver activation voltage vact is high, the supply voltage Vbat is provided to the voltage divider 33, and the supply voltage Vstandby is provided to the charge pump 32. When the driver activation voltage vact is low, both voltages are cut off. It is of course possible to flip the control logic so that when it is low, the voltages are on, and when it is high, voltages are off.

[0051] With two complementing power sources 31 and 32, a risk of an insufficient gate drive voltage Vdrv can be minimized. The second power supply 32 generates a sufficient supply voltage from the supply voltage Vstandby, thereby providing a sufficient gate drive voltage Vdrv, even when the supply voltage Vbat from the first voltage source 31 is not available, or is at an insufficient level. At the same time, the first power supply 31, when active, provides means for producing a sufficient gate drive voltage Vdrv very quickly.

[0052] While the embodiment of FIGURE 2 presents two parallel power sources 31 and 32, either one of the power sources may be omitted depending on the application. For example, if the power supply of the ECU has sufficiently high voltage to alone drive the gate drive voltage Vdrv even in the worst-case scenario, the charge pump may not be necessary. Alternatively, the switch driver circuit may also be implemented only with a charge pump.

[0053] The configurable termination resistance 2 of a line termination circuit according to the present disclosure may be implemented in various ways.

[0054] In FIGURE 2, the semiconductor switch unit 22 of the configurable termination resistance 2 is presented as simplified, generic switch connected between one end of the resistor assembly 21 and the CANL line 12 of the CAN bus. In some embodiments of a line termination circuit according to the present disclosure, the semiconductor switch unit 22 may be made of two FETs forming a bidirectional switch in order to be able to block current to both directions. The FETs may be a pair of N-channel enhancement type MOSFETs, which are widely available, for example.

[0055] FIGURE 4 shows a simplified diagram of an example implementation of a configurable termination resistance 2 according to the present disclosure where its semiconductor switch unit is in the form of a bidirectional switch. The example implementation may represent the configurable termination resistance 2 of FIGURE 1 and / or FIGURE 2, for example.

[0056] In FIGURE 4, the configurable termination resistance 2 comprises a semiconductor switch unit 22 in series with a resistor assembly 21 between the two signal lines CANH 11 and CANL 12 of the CAN bus. The semiconductor switch unit 22 comprises two FETs in the form of n-channel MOSFETs 221 and 222 connected to form a commonsource bidirectional switch. In some embodiments, the semiconductor switch unit 22 also comprises a biasing resistor (not shown in FIGURE 4) connecting sources of the FETs to a reference potential.

[0057] When choosing the FETs for the semiconductor switch unit of the configurable termination resistance, it may be desirable the select a switch that it can handle the maximum allowed short circuit current of the CAN transceiver. For example, in some embodiments, the maximum allowed short circuit current of the CAN transceiver is 110mA. The drain-to- source on resistance of the FETs is preferably low enough so that, when the FET is in the conducting state, the resistance value of the whole configurable termination resistance fulfils the requirement of 120Q ± 5% from CAN standard.

[0058] In FIGURE 4, gates of both MOSFETs 221 and 222 are driven with gate drive voltage Vdrv- As shown in FIGURE 4, a pull-down resistor 223 may be used to pull the gate drive voltage Vdrv down when the termination is configured off.

[0059] In a semiconductor switch unit of a line termination circuit according to the present disclosure, a maximum allowed gate-source voltage of the FETs is preferably higher than a maximum continuous voltage value of the gate drive voltage Vdrv, taking into account a possible negative common-mode voltage of the CAN bus. Alternatively, or in addition, a clamp circuit may be used to protect the gate from over-voltage situations that might occur for example when nominal battery voltage is connected to it and the common-mode voltage on the CAN bus is low (minimum is -12V, for example). FIGURE 4 shows a Zener diode 224 connected between the sources and the gates of the two MOSFETs 221 and 222 in order to limit the control voltage to remain below a set limit. The Zener diode 224 acts as overvoltage protection for the gates of the semiconductor switches of the semiconductorswitch unit. Its function is to clamp the gate-source voltage of the MOSFETs 221 and 222 to a safe level, which depends on the maximum voltage rating specified for the transistors used. Typically, it is +20V or +30V for small transistors with low power ratings. The voltage between the gates and the sources of the MOSFETs 221 and 222 may have to be clamped when a maximum value of the gate drive voltage Vdrv is being applied to the gates and a minimum common-mode voltage occurs on the CAN bus. Also, if the CAN bus is shorted to negative voltage (ISO 11898-2 defines -27V / +40V short circuit tolerance), clamping may be required.

[0060] While the above examples describe the semiconductor switch unit being configured as a bidirectional switch, other configurations may also be used. For example, in some embodiments, the semiconductor switch unit is made of a single n-channel enhancement type MOSFET. Similar to the embodiment of FIGURE 4, the source of the MOSFET of the semiconductor switch unit may be connected to an CANE line of the line pair, and the drain of the MOSFET may be connected to the resistor assembly.

[0061] It is also possible to tie the semiconductor switch unit to the potential of the CANH, and control it with a negative voltage. In such embodiments, an inverting charge pump may be used, for example. However, there may not be existing negative supply voltages in the parent unit to be used as the gate drive voltage.

[0062] Further, as explained in relation to the embodiments of FIGURES 1 and 2, while presented as a single resistor, the resistor assembly 21 of the configurable termination resistance in FIGURE 4 may be formed by a plurality of resistors in series and / or in in parallel.

[0063] As mentioned earlier, in some embodiments, the resistor assembly is formed by two series-connected halves. FIGURE 5 shows a configurable termination resistance 2 with a semiconductor switch unit 22 connected in series with a first half 21a and a second half 21b of a resistor assembly 21. The semiconductor switch unit 22 is connected between the two halves 21a and 21b. In some embodiments, the semiconductor switch unit 22 is made of two FETs forming a bidirectional switch. The construction of the semiconductor switch unit 22 in FIGURE 5 may correspond to the semiconductor switch unit 22 of FIGURE 4, for example. The two halves 21a and 21b may be formed by two equally sized resistor subassemblies that each have the resistance of one half of the characteristic impedance of the wire, i.e., 60Q. In some embodiments, an interconnection between the two FETs of thebidirectional switch is connected to a reference potential via a capacitor. For example, if semiconductor switch units similar to that of FIGURE 4, the common-source connection of the FETs 221 and 222 may be connected to ground via a capacitor. In this manner, high frequency noise can be filtered while avoiding unbalanced termination of the CANL and CANH lines.

[0064] A line termination circuit according to the present disclosure can be used in a large variety of different applications. For example, as discussed earlier, the above-discussed line termination circuit may be used in an ECU, for example. An ECU may comprise control electronics one or more instances of the line termination circuit, for example. With the line termination circuit, the ECU may be placed anywhere in the CAN bus, including at the physical ends of the CAN bus or between the two physical ends.

[0065] The above-discussed line termination circuits or ECUs implementing such a line termination circuit may be used in various demanding applications. Such an ECU may be used in non-road mobile machinery, NRMM, for example. Some examples of NRMM are excavators, forestry machinery, mining machinery, agricultural machinery, etc.

[0066] In NRMM applications, the electronics may be powered with a battery. Minimizing power consumption may be desirable, and it may be necessary to allow a low- power mode (e.g., sleep mode) of the equipment. Further, there may be requirements regarding the common-mode voltage range. In some embodiments, the circuit may have to be able to work with common-mode voltages from -2V to +7V in the CAN bus according to ISO 11898-3 standard. In other applications, the common-mode voltage tolerance may be even higher, e.g., from -12V to +12V. At the same time, there may be a requirement for low power consumption. Thus, it may be desirable to keep current consumption of the termination circuit as small as possible. In some embodiments a hard limit for the current consumption may be 1 mA. In addition, it may be desirable that the line termination circuit has a sufficient vibration and shock tolerance of the unit. The circuit should preferably also tolerate should preferably also tolerate temperatures from -40°C to +105 °C, and its components temperatures from -40°C to +125°C. A line termination circuit according to the present disclosure can be adapted to fulfil all these requirements.

[0067] While the line termination circuit according to the present disclosure is mostly discussed in the context of demanding applications, such as in NRMM, it can also be used in other fields of application, such as in heavy or light road vehicles.

[0068] It is to be understood that the embodiments disclosed in the present disclosure are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[0069] Reference throughout this specification to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Where reference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed.

[0070] As used herein, a plurality of items, structural elements, compositional elements, and / or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and examples according to the present disclosure may be referred to along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations.

[0071] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the preceding description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments according to the present disclosure. One skilled in the relevant art will recognize, however, that the embodiments can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the embodiments.

[0072] While the examples are illustrative of the principles of the present disclosure in one or more particular applications, itis apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made withoutthe exercise of inventive faculty, and without departing from the principles and concepts the present disclosure. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0073] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", that is, a singular form, throughout this document does not exclude a plurality.

[0074] As used herein, “at least one of the following: ” and “at least one of ” and similar wording, where the list of two or more elements are joined by “and” or “or”, mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.ACRONYMS LISTCAN Controller area networkCANH CAN High (signal line)CANL CAN Low (signal line)CMOS Complementary metal-oxide-semiconductor ECU Electronic control unitFET Field-effect transistorIC Integrated chipICE Internal combustion engineMCU Microcontroller unitMOSFET Metal-oxide-semiconductor field-effect transistor NRMM Non-road mobile machineryREFERENCE SIGNS LIST1 CAN transceiver2 Configurable termination resistance3 Switch driver circuit4 Control circuit11 CANH signal line12 CANL signal line21 Resistor assembly21a, 21b Halves of resistor assembly22 Semiconductor switch unit31 First power supply32 Second power supply (charge pump)33 Voltage selector34 Switch41 Memory unit42 Voltage regulator43 Pull-down resistor221 MOSFET222 MOSFET223 Pull-down resistor224 Zener diode

Claims

CLAIMS:

1. A line termination circuit for a signal line pair of a Controller Area Network, CAN, bus, the line termination circuit comprising:- a configurable termination resistance (2) comprising a resistor assembly (21) and a semiconductor switch unit (22) connected in series between two lines of the line pair, wherein the semiconductor switch unit (22) comprises at least one field-effect transistor, FET, configured to be controlled to a conducting state or to a non-conducting state with a gate drive voltage at its gate,- a switch driver circuit (3) configured to generate the gate drive voltage in response to a driver activation voltage, and- a control circuit (4) configured to generate the driver activation voltage at least partially based on a termination control command at a termination control input of the control circuit (4), wherein- the control circuit comprises a memory unit (41) configured to store a representation of a state of the configurable termination resistance (2) based on the termination control command and reproduce the stored representation at an output of the memory unit (41),- the driver activation voltage is generated at least partially based on the stored representation at the output of the memory unit (41), and- the gate drive voltage generated by the switch driver circuit (3) has a greater voltage swing than the driver activation voltage.

2. A line termination circuit according to claim 1, wherein- the control circuit is configured to recognize two different termination control commands: a first command for setting the configurable termination resistance on and a second command for setting the termination resistance off, and- the memory unit is configured to store the representation of the state of the configurable termination resistance based on the recognized command.

3. A line termination circuit according to claim 1, wherein the termination control command is in the form of a voltage pulse and the memory unit is being configured to change its output voltage from a low voltage level to a high voltage level in response to the voltage pulse.

4. A line termination circuit according to any one of the preceding claims, wherein the switch driver circuit comprises a first power source configured to generate a first voltage, the first voltage being used as the gate drive voltage.

5. A line termination circuit according to claim 4, wherein the driver circuit further comprises- a second power source in the form of a charge pump configured to convert an input voltage into a second voltage in response to the driver activation voltage, and- a voltage selector configured to select a higher voltage from the first and second voltage and use the selected voltage as the gate drive voltage.

6. A line termination circuit according to any one of claims 1 to 3, wherein the driver circuit further comprises- a power source in the form of a charge pump configured to convert an input voltage into the gate drive voltage in response to the driver activation voltage.

7. A line termination circuit according to any one of the preceding claims, wherein the CAN bus has a common-mode voltage tolerance range of at least -10V to 10V.

8. A line termination circuit according to any one of the preceding claims, wherein- the semiconductor switch unit is made of a n-channel enhancement type MOSFET,- the source of the MOSFET is connected to a CANL line of the line pair,- the drain of the MOSFET is connected to the resistor assembly.

9. A line termination circuit according to any one of claims 1 to 7, wherein- the semiconductor switch unit is made of two FETs forming a bidirectional switch, and- the semiconductor switch unit connected between one end of the resistor assembly and the CANL line.

10. A line termination circuit according to any one of claims 1 to 7, wherein- the resistor assembly is formed by two separate halves, and- the semiconductor switch unit is connected between the two halves of the resistor assembly.

11. A line termination circuit according to claim 10, wherein- the semiconductor switch unit is made of two FETs forming a bidirectional switch, and- an interconnection between the two FETs is connected to a ground potential via a capacitor.

12. A line termination circuit according to any one of the preceding claims, wherein a Zener diode is connected between the source and the gate of the semiconductor switch unit in order to limit the control voltage to remain below a set limit.

13. An electronic control unit, ECU, comprising a line termination circuit according to any one of the preceding claims.

14. Non-road mobile machinery, NRMM, comprising at least one ECU according to claim 13.

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