Isolated communication device and multi-level encoding method therefor

Abstract

The present disclosure describes an isolated communication device and a multi-level encoding method therefor. The isolated communication device includes a transceiver (10) and an isolation circuit (20). The isolation circuit (20) includes an isolation transformer (T1) having a driver-side winding and a line-side winding, a first serial resistor (R11) that is coupled with a first end of the driver-side winding, and a second serial resistor (R12) that is coupled with a second end of the driver-side winding. The transceiver (10) transmits a differential signal through the first serial resistor (R11) and the second serial resistor (R12), and receives the differential signal, bypassing the first serial resistor (R11) and the second serial resistor (R12). The isolated communication device reduces power consumption by arranging serial resistors at the driver side of the isolation transformer, and improve impedance matching and strengthen bulk current injection (BCI) immunity by arranging serial resistors at both sides of the isolation transformer.

Description

ISOLATED COMMUNICATION DEVICE AND MULTI-LEVEL ENCODING METHOD THEREFORTechnical Field

[0001] The present disclosure generally relates to electronic circuits, and more particularly, to an isolated communication device and a multi-level encoding method therefor.Background Art

[0002] In the battery power system of an electric vehicle (EV), numerous battery cells within a battery pack are interconnected to provide adequate power for propelling the electric vehicle. A battery management system (BMS) is integrated into the battery power system to monitor and manage the battery cells within the battery pack, ensuring the secure and efficient functionality of the battery system.

[0003] The battery management system (BMS) typically includes several control units which communicate with each other via a controller area network (CAN) bus. An isolated communication physical layer (IsoCom) is particularly used inside the BMS to guarantee electrical isolation from external electromagnetic interference (EMI), and from a high level of voltage and / or current of the battery pack. The IsoCom should ideally be designed to minimize electric-magnetic Susceptibility (EMS) and strengthen bulk current injection (BCI) immunity, so as to ensure timely and effective communication between the control units.

[0004] The control units in the BMS are typically coupled with each other through transmission lines, such as twisted pair cables. The IsoCom should ideally be designed to have impedance matching between the transmitter and receiver of the control units. The transmission lines must be terminated with an impedance equal to the characteristic line impedance at both the transmitter and receiver ends to ensure signal integrity during communication.

[0005] Conventional isolated communication devices with the IsoCom may include an isolation transformer or an isolation capacitor. The isolation transformer is an attractive solution because it prevents a high level of current from flowing from one side to the other. However, isolated communication devices may have increased power consumption if a parallel resistor is coupled with the transformer winding.

[0006] The turns ratio N of the isolation transformer is typically 1, but it may deviate from this value due to fluctuations in the manufacturing process. A resistor at one side of the isolation transformer has an equivalent resistance at the other side of the isolation transformer, which depends on the turns ratio N of an isolation transformer. Moreover, an equivalent winding impedance of the isolation transformer varies at different frequencies with the turns ratio N of an isolation transformer. It is difficult to achieve impedance matching in the isolated communication devices using an isolation transformer.

[0007] Therefore, it is required that the isolated communication device reduces power consumption and improves impedance matching.Summary of the Disclosure

[0008] IAccording to one aspect of the present disclosure, there is a provided an isolated communication device, comprising: a transceiver that transmits and receives a differential signal through first and second transmission lines; and an isolation circuit that is coupled between the transceiver and the first and second transmission lines, wherein the isolation circuit comprises an isolation transformer having a driver-side winding and a line-side winding, a first serial resistor that is coupled with a first end of the driver-side winding, and a second serial resistor that is coupled with a second end of the driver-side winding, the transceiver transmits the differential signal through the first serial resistor and the second serial resistor to the driver-side winding of the isolation transformer, and receives the differential signal, bypassing the first serial resistor and the second serial resistor, from the driver-side winding of the isolation transformer.

[0009] According to another aspect of the present disclosure, there is provided a multi-level encoding method for an isolated communication device. The isolated communication device includes an isolation transformer with a driver-side winding and a line-side winding, and serial resistors that are coupled with the driver-side winding and the line-side winding of the isolation transformer. The multi-level encoding method comprises: configuring a circuit for discrete signal levels; and encoding data into successive multi-bit signals, where each bit signal includes at least two symbol bits and one end bit, wherein the two symbol bits represent 1 with a positive level and a negative level, and 0 with a negative level and a positive level, and the one end bit is a zero level.Detailed Description of the Disclosure

[0010] The foregoing and other objects, features and advantages of the disclosure will be apparent from the following more particular description of preferred embodiments of the disclosure, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the disclosure.

[0011] FIG. 1 illustrates a conventional battery power system of an electric vehicle.

[0012] FIG. 2 illustrates isolated communication between a battery monitor unit and a battery control unit in the battery power system.

[0013] FIG. 3 illustrates an exemplary isolated communication device in the battery monitor unit according to an embodiment of the present disclosure.

[0014] FIG. 4 illustrates an exemplary battery monitor unit with serial resistors in a chip.

[0015] FIG. 5 is a flow chart of multi-level encoding method for an isolated communication device according to an embodiment of the present disclosure.

[0016] FIG. 6 illustrates an exemplary bit signal according to an embodiment of the present disclosure.Specific Embodiment

[0017] Many specific details of the present disclosure, such as the structure, material, dimensions, treatment processes, and techniques of the components, are described below for more clear understanding of the present disclosure. However, as will be appreciated by those skilled in the art, the present disclosure may not be practiced in accordance with these specific details.

[0018] It should also be noted that in this description, relational terms such as first and second are merely used to distinguish one entity or operation from another, and do not necessarily require or imply that there is any such actual relationship or sequence among these entities or operations. Furthermore, the word "include", "contain", or any other variation thereof is intended to cover non-exclusive inclusion, so that a process, method, article, or device including a series of elements includes not only those elements, but other elements that are not explicitly listed or elements inherent to such process, method, article, or device. In the absence of further limitations, elements defined by the phrase "comprises a…" do not exclude the presence of additional identical elements in the process, method, article, or device that includes the elements.

[0019] It will be appreciated by those of ordinary skill in the art that the words "during", "when", and "while" used herein in connection with circuit operation are not strict terms for actions that occur immediately at the beginning of a start action, but that there may be some small but reasonable one or more delays after a reaction action initiated by a start action, such as various transmission delays, etc. As used herein, the word "approximately" or "substantially" means an element has a parameter that is expected to approximate the declared value or location. However, as is well known in the art, there are always minor deviations that make it difficult to have the value or position to be strictly the declared value. It has been properly determined in the art that a deviation of at least ten percent (10%) is a reasonable deviation from the precise desired target described (for a doping concentration of semiconductor, at least twenty percent (20%)). When a signal is described in the context of a state, an actual voltage value or logic state of the signal (e.g. "1" or "0") depends on whether positive or negative logic is used.

[0020] It will be appreciated by those of ordinary skill in the art that the word "circuit" may include single or multiple combinations of hardware circuits, programmable circuits, state machine circuits, and / or components capable of storing instructions which are executed by a programmable circuit. Conversely, when the element is said to be "directly coupled" or "directly connected" to another element, it means that there is no intermediate element therebetween.

[0021] FIG. 1 illustrates a conventional battery power system of an electric vehicle. The battery power system is used to provide adequate power for propelling the electric vehicle.

[0022] As shown in FIG. 1, the battery power system 100 includes numerous battery cells 111 which are interconnect to provide power for propelling the electric vehicle. Each cell stores and releases electrical energy through chemical reactions. The battery cells 111 are typically lithium-ion cells due to their high energy density, long life cycle, and reliability. The battery cells 111 may be arranged in series or parallel configurations and grouped into battery modules 110-1 to 110-N, to achieve the desired voltage and capacity. The battery modules 110-1 to 110-N may be housed in a protective casing to form a battery pack. The battery power system 110 may have one or more battery packs in view of the power requirements. Although not shown in the figure, the battery packs may be connected to an inverter, which converts the DC power from the battery pack into AC power and supplies the AC power to electric motors of the electric vehicle.

[0023] The battery power system 100 further includes a battery management system for controlling the charging and discharging functions of the battery cells. The battery management system may include battery monitor units 112 inside the battery modules 110-1 to 110-N, and a battery control unit 120 outside the battery modules 110-1 to 110-N. The battery control unit 120 and the battery monitor units 112 may communicate with each other via a controller area network (CAN) bus.

[0024] The battery monitor units 112 are responsible for monitoring the individual cell voltages, temperatures, and overall health of the cells within each module. They provide real-time data and diagnostics to ensure safe and efficient operation. The battery control unit 120 collects this data and makes higher-level decisions regarding battery management, such as balancing the charge among cells, protecting against overcharging or deep discharging, and managing thermal conditions.

[0025] FIG. 2 illustrates isolated communication between a battery monitor unit 112 and a battery control unit 120 in the battery power system 100. An isolated communication physical layer is designed here in the CAN bus to prevent ground loops, protect against high voltage transients, and ensure safety and reliability in electrically noisy environments.

[0026] The battery monitor unit 112 includes an isolated communication device 101, and the battery control unit 120 includes an isolated communication device 102. The isolated communication device 101 and the isolated communication device 102 are connected with each other via transmission lines 103 of a twisted pair cable. Both the isolated communication devices 101 and 102 support bidirectional communication, allowing each of the battery monitor unit 112 and the battery control unit 120 to transmit and receive data via the transmission lines 103.

[0027] Specifically, as shown in FIG. 3, the isolated communication device 101 in the battery monitor unit 112 includes a transceiver 10 and an isolation circuit 20. The isolation circuit 20 is coupled between the transceiver 10 and the transmission lines 103. The transceiver 10 transmits and receives a differential signal through the transmission lines 103.

[0028] The isolation circuit 20 includes an isolation transformer T1, a first serial resistor R11, and a second serial resistor R12. The isolation transformer T1 has a driver-side winding and a line-side winding. The first serial resistor R11 is defined as a serial resistor because it is coupled between a first output of the transceiver 10 and a first end of the driver-side winding. The second serial resistor R12 is also defined as a serial resistor because it is coupled between a second output of the transceiver 10 and a second end of the driver-side winding.

[0029] The transceiver 10 transmits the differential signal through the first serial resistor R11 and the second serial resistor R12 to the driver-side winding of the isolation transformer T1, and receives the differential signal, bypassing the first serial resistor R11 and the second serial resistor R12, from the driver-side winding of the isolation transformer T1. Compared with a parallel resistor which is coupled between the first end and the second end of the driver-side winding, the first serial resistor R11 and second serial resistor R12 can reduce driving current of the transceiver 10 to one half for the same transmission power. The isolated communication device 101 will reduce power consumption in the communication, because the energy loss in the isolation circuit 20 decreases.

[0030] Preferably, the isolation circuit 20 includes a third serial resistor R13, and a fourth serial resistor R14. The third serial resistor R13 is defined as a serial resistor because it is coupled between a first end of the line-side winding and a first transmission line of the transmission lines 103. The fourth serial resistor R14 is also defined as a serial resistor because it is coupled between a second end of the line-side winding and a second transmission line of the transmission lines 103.

[0031] Each of the first serial resistor R11 and the second serial resistor R12 has a first resistance Rd, and has a first equivalent resistance Rel at the line-side winding of the isolation transformer T1, which depends on a turns ratio N of the isolation transformer T1. Each of the third serial resistor R13 and the fourth serial resistor R14 has a second resistance Rl, and has a second equivalent resistance Red at the driver side of the isolation transformer T1, which depends on a turns ratio N of the isolation transformer T1.

[0032] The transceiver 10 transmits the differential signal through the first serial resistor R11 and the second serial resistor R12, the isolation transformer T1, and the third serial resistor R13 and the fourth serial resistor R14, to the transmission lines 103.

[0033] A sum of the first equivalent resistance Rel and the second resistance Rl matches 1 / 2 of the line impedance Zcl of the transmission lines 103. Here, the word “match” means “be approximately equal to”, but not “be exactly equal to”. Assuming that the turns ratio N of the isolation transformer T1 is 1:1 and the line resistance Zcl is 120 Ohm, each of the first serial resistor R11 and the second serial resistor R12 may have a first resistance Rd≈k*Zcl / 2 Ohm, and each of the third serial resistor R13 and the fourth serial resistor R14 may have a second resistance Rl≈(1-k)*Zcl / 2 Ohm, so that the isolation circuit 20 matches the line impedance Zcl of the first and second transmission lines.

[0034] Here, the ratio k ranges from 0.1 to 0.9.  The ratio k may be optimized for the performance of the isolated communication device 101. It has been found that the power consumption in the transmission mode can be reduced and the signal-to-noise ratio can be increased, by configuring the ratio k to be smaller than 0.7.

[0035] By dividing an equivalent resistance of the isolation circuit 20 into two parts at both sides of the isolation transformer T1, the impedance matching can be achieved both in the transmission mode and in the receiving mode, even in case that the turns ratio N of the isolation transformer T1 is not equal to 1. At least the third serial resistor R13 and the fourth serial resistor R14 directly contribute to the equivalent resistance of the isolation circuit 20 in the transmission mode, which will not be affected by the turns ratio N of the isolation transformer T1.

[0036] Thus, the isolation circuit 20 will have improved impedance matching because the turns ratio N of the isolation transformer affects only some of the serial resistors, compared with the case that all of the serial resistors are arrange at the driver side of the isolation transformer T1. The isolation circuit 20 allows that the isolation transformer T1 has a turns ratio varying from 0.8 to 1.2.

[0037] Moreover, the first resistance of the first serial resistor R11 and the second serial resistor R12 and the second resistor resistance of the third resistor R13 and the fourth serial resistor R14 may be optimized for impedance matching by calculating an equivalent resistance of the isolation circuit 20 for an actual turns ratio N of the isolation transformer T1, as mentioned above. Thus, the variation of the turns ratio N of the isolation transformer T1 will be compensated by optimizing the serial resistors at both sides of the isolation transformer T1.

[0038] Furthermore, in a case that an interference signal is injected from the transmission lines 103, the transceiver 10 will received an divided voltage due to the serial resistors R11 and R12 and the serial resistors R13 and R14 which are arranged at both sides of the isolation transformer T1. The isolated communication device 101 will strengthen bulk current injection (BCI) immunity, because the impact of the interference signal on the transceiver 10 is reduced by the serial resistors at both sides of the isolation transformer T1.

[0039] Preferably, the isolation circuit 20 includes a first low-pass filter 21 and a second low-pass filter 22, but this is not intended to limit the scope of the disclosure. Instead, the first low-pass filter 21 and the second low-pass filter may be omitted if the interference signal is insignificant.

[0040] The first low-pass filter 21 includes an inductor L1 which is coupled between the first serial resistor R11 and the first end of the first winding of the isolation transformer T1, and a capacitor C1 which is coupled between an intermediate node of the first serial resistor R11 and the inductor L1 and ground. The second low-pass filter 22 includes an inductor L2 which is coupled between the second serial resistor R12 and the second end of the first winding of the isolation transformer T1, and a capacitor C2 which is coupled between an intermediate node of the second serial resistor R12 and the inductor L2 . The inductors L1, L2 of the first low-pass filter 21 and the second low-pass filter 22 may be coupled as a transformer to suppress common-mode noise, but this is not intended to limit the scope of the disclosure.

[0041] FIG. 4 illustrates an exemplary battery monitor unit with serial resistors in a chip. The battery monitor unit 112 may be used for isolated communication in the battery power system as shown in FIG. 2.

[0042] As shown in FIG. 4, the battery monitor unit 112 includes a logic circuit 21 and  some portions of the isolated communication device 101, which are integrated into one chip and have two pins PIN1 and PIN2.

[0043] The logic circuit 21 collects battery data from various sensors that monitor voltage, current, temperature, and other relevant parameters of the battery cells, and controls the charging and discharging functions of the battery cells. Moreover, the logic circuit 21 encodes battery data into structured data packet or decodes control instructions, which are also structured data packet and received from a battery control unit 120.

[0044] The transceiver 10 is a bidirectional transceiver which includes a transmitter TX, and two receivers RX1 and RX2. The transmitter TX has a logic interface which receives data packet from the logic circuit 21 and an analog interface which outputs a differential signal according to bits of the data packet. The transmitter TX converts high and low logic inputs to a differential signal with either a positive level, a negative level, or a zero level. Each of the receivers RX1 and RX2 has an analog interface which receives a differential signal from the transmission lines 103 and a logic interface which outputs bits of the data packet. The receiver RX1 converts a differential voltage into a positive polarity of the differential voltage, and the receiver RX2 converts a differential voltage into a negative polarity of the differential voltage. The differential voltage is a combination of the positive polarity and the negative polarity of the differential voltage.

[0045] The first serial resistor R11 and the second serial resistor R12 of the isolation circuit 20 are integrated into the chip, together with the transceiver 10. The transmitter TX is coupled to the pins PIN1 and PIN2 of the chip, through the first serial resistor R11 and the second serial resistor R12. Each of the receivers RX1 and RX2 is directly coupled to the pins PIN1 and PIN2 of the chip, bypassing the first serial resistor R11 and the second serial resistor R12. Each of the first serial resistor R11 and the second serial resistor R12 inside the chip may have fixed first resistance, and each of the third serial resistor R13 and the fourth serial resistor R14 may have a second resistance which depends on variation of the turns ratio N of the isolation transformer T1. With the first serial resistor R11 and the second serial resistor R12 being integrated into the chip, the transmitter TX and the receivers RX1 and RX2 may use only two pins PIN1 and PIN2 of the chip for bidirectional communication, which reduces the number of pins of the chip and simplifies peripheral components.

[0046] FIG. 5 is a flow chart of multi-level encoding method for an isolated communication device according to an embodiment of the present disclosure. The multi-level encoding method may be implemented in the battery monitor unit 112 or in the battery control unit 120 shown in FIG. 2.

[0047] In step S01, the transceiver 10 is configured to have discrete signal levels, including a positive level, a negative level, or a zero level.

[0048] In step S02, the logic circuit 21 encodes battery data into structured data packet, and the transceiver 10 converts the structured data packet into successive multi-bit signals.

[0049] As shown in FIG. 6, each bit signal of the data packet has two symbol bits and one end bit, with time-equal bit periods. The two symbol bits represent logic 1 with a positive level and a negative level in sequence, and logic 0 with a negative level and a positive level in sequence, and the one end bit is a zero level.

[0050] The isolated communication device 101 will strengthen bulk current injection (BCI) immunity, because the impact of the interference signal on the transceiver 10 is reduced by the serial resistors at both sides of the isolation transformer T1. The low-pass filters 21 and 22 in the isolation circuit 20 will have a smaller time constant because a narrow frequency range of noise needed to be filtered out, or even be omitted. Thus, the differential signal will establish the desired level faster because the magnetic current across the transmission lines will increase or decrease quickly. Thus, each bit period of the bit signal will be decreased to be about 100ns. The bit cycle of the bit signal will be about 300ns for the three time periods, which is smaller than a conventional encoding method. Thus, the transmission speed may be increased because the bit cycle of the bit signal is shortened.

[0051] In accordance with the embodiments of the present disclosure, such as described above, these embodiments do not describe all the details in detail, nor do they limit the disclosure to the specific embodiments described. Obviously, a lot of modifications and changes can be made based on the above description. These embodiments are selected and specifically described in this specification in order to better explain the principles and practical applications of the present disclosure, so that those skilled in the art can make good use of the present disclosure and its modifications on the basis of the present disclosure. The present disclosure is limited only by the claims and their full scope and equivalents.

Claims

1.An isolated communication device (101; 102), comprising:a transceiver (10) that transmits and receives a differential signal through first and second transmission lines (103); and an isolation circuit (20) that is coupled between the transceiver (10) and the first and second transmission lines (103),wherein the isolation circuit (20) comprises an isolation transformer (T1) having a driver-side winding and a line-side winding, a first serial resistor (R11) that is coupled with a first end of the driver-side winding, and a second serial resistor (R12) that is coupled with a second end of the driver-side winding, the transceiver (10) transmits the differential signal through the first serial resistor (R11) and the second serial resistor (R12) to the driver-side winding of the isolation transformer (T1), and receives the differential signal, bypassing the first serial resistor (R11) and the second serial resistor (R12), from the driver-side winding of the isolation transformer (T1). 2.The isolated communication device (101; 102) according to claim 1, wherein the isolation circuit (20) comprises a third serial resistor (R13) that is coupled between a first end of the line-side winding and the first transmission line, and a fourth serial resistor (R14) that is coupled between a second end of the line-side winding and the second transmission line.3.The isolated communication device (101; 102) according to claim 2, wherein the isolation circuit (20) has an equivalent impedance which matches a line impedance of the first and second transmission lines (103).4.The isolated communication device (101; 102) according to claim 3, wherein each of the first serial resistor (R11) and the second serial resistor (R12) has a first resistance with a fixed value, and each of the third serial resistor (R13) and the fourth serial resistor (R14) has a second resistance that depends on a turns ratio N of the isolation transformer (T1). 5.The isolated communication device (101; 102) according to claim 4, wherein the first serial resistor (R11) and the second serial resistor (R12) are integrated with the transceiver (10) in one chip, and the third resistor and the fourth resistor are located outside the one chip.6.The isolated communication device (101; 102) according to claim 4, wherein each of the first serial resistor (R11) and the second serial resistor (R12) has a first equivalent resistance at the line-side winding of the isolation transformer (T1), and a sum of the first equivalent resistance and the second resistance matches 1 / 2 of the line impedance of the first and second transmission lines (103).7.The isolated communication device (101; 102) according to claim 2, wherein the transceiver (10) comprises:a transmitter (TX) which has differential outputs that are coupled with the driver-side winding of the isolation transformer (T1), through the first serial resistor (R11) and the second serial resistor (R12) ; a first receiver (RX1) which has differential inputs that are coupled with the driver-side winding of the isolation transformer (T1), bypassing the first serial resistor (R11) and the second serial resistor (R12); and a second receiver (RX2) which has differential inputs that are coupled with the driver-side winding of the isolation transformer (T1), bypassing the first serial resistor (R11) and the second serial resistor (R12), wherein the first receiver (RX1) and the second receiver (RX2) have differential inputs of opposite polarities and have outputs which are combined to be a differential signal. 8.The isolated communication device (101; 102) according to claim 2, wherein the isolation circuit further comprises:a first low-pass filter (21) that is coupled between the first serial resistor (R11) and the first end of the first winding of the isolation transformer (T1); and a second low-pass filter (22) that is coupled between the second serial resistor (R12) and the second end of the first winding of the isolation transformer (T1). 9.The isolated communication device (101; 102) according to claim 8, wherein each of the first low-pass filter (21) and the second low-pass filter (22) is an LC filter having an inductor (L1; L2) and a capacitor (C1; C2).10.The isolated communication device (101; 102) according to claim 9, wherein the inductors (L1, L2) of the first low-pass filter (21) and the second low-pass filter (22) are coupled as a transformer. 11.The isolated communication device (101; 102) according to claim 1, wherein the isolation circuit (20) allows that the turns ratio N of the isolation transformer (T1) varies from 0.8 to 1.2.12.A multi-level encoding method for an isolated communication device (101; 102) having an isolation transformer (T1) with a driver-side winding and a line-side winding, and serial resistors (R11, R12, R13, R14) that are coupled with the driver-side winding  and the line-side winding of the isolation transformer (T1), comprising:configuring a transceiver for discrete signal levels; andencoding data into successive multi-bit signals, each bit signal having at least two symbol bits and one end bit, wherein the two symbol bits represent 1 with a positive level and a negative level in sequence, and 0 with a negative level and a positive level in sequence, and the one end bit is a zero level. 13.The multi-level encoding method according to claim 12, wherein the bit signal has time-equal bit periods for the two symbol bits and the end bit.14.The multi-level encoding method according to claim 12, wherein the serial resistors (R11, R12, R13, R14) are used to increase transmission speed.

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