Sensor and digital communication method

Abstract

The present invention relates to a sensor and a digital communication method. Provided herein is a digital communication bus suitable for automotive applications and a bus controller and sensor using the bus and its associated communication method. An exemplary sensor includes a clock signal generator, a bus interface coupled to a differential signal conductor to detect periodic synchronization pulses from a bus controller, and a controller to align a clock signal from the clock signal generator with the periodic synchronization pulses. The bus interface sends digital data to the bus controller between the periodic synchronization pulses, using the clock signal to control symbol transitions.

Description

TECHNICAL FIELD

[0001] The present disclosure relates generally to digital communication buses suitable for automotive applications, and more particularly to a clock synchronization method and sensors employing such a method. BACKGROUND

[0002] Modern automobiles are equipped with a large variety of sensors. For example, a passenger car is typically equipped with a motor position sensor to monitor engine speed, estimate fuel consumption, and provide engine diagnostics. Traditionally, such "high speed" sensors employ a resolver with an analog interface for in-phase and quadrature-phase output signals. To provide protection against electromagnetic interference and emissions, electromagnetic compatibility is maintained using relatively expensive filters, and each of the output signals is typically carried as a differential signal over a twisted pair. While a digital interface for such sensors potentially provides more robust operation at reduced implementation cost, existing digital buses suitable for automotive environments are unable to support the necessary data rates. SUMMARY

[0003] Accordingly, disclosed herein are digital communication buses suitable for automotive applications, as well as bus controllers and sensors using the buses and their associated communication methods.

[0004] According to one aspect of the present disclosure, a sensor is provided, the sensor comprising: a clock signal generator; a bus interface coupled to a differential signal conductor to detect periodic synchronization pulses from a bus controller; and a controller to align a clock signal from the clock signal generator with the periodic synchronization pulses, the bus interface to transmit digital data to the bus controller between the periodic synchronization pulses and to control symbol transitions using the clock signal.

[0005] In one embodiment, in the sensor, the controller uses a leading edge of the synchronization pulses to determine a period of the clock signal.

[0006] In one embodiment, in the sensor, the controller uses a trailing edge of the synchronization pulses to set a phase of the clock signal.

[0007] In one embodiment, in the sensor, as part of said alignment, the controller performs a coarse calibration phase before the bus interface begins transmitting digital data, and performs an adaptive tracking phase after the bus interface begins transmitting digital data, the controller adjusting a period of the clock signal to match 1 / N of a period of the synchronization pulses, N being an integer.

[0008] In one embodiment, in the sensor, the sensor further comprises transducer electronics to collect measurements independent of said clock signal, the controller using the clock signal to capture said measurements and derive digital data therefrom.

[0009] According to another aspect of the disclosure, there is provided a method of digital communication, the method comprising: generating a local clock signal; aligning the local clock signal with periodic synchronization pulses from a bus controller; and transmitting digital data to the bus controller between the periodic synchronization pulses and using the clock signal to control symbol transitions.

[0010] In one embodiment, in the method of digital communication, the aligning comprises deriving a period of the clock signal from a leading edge of the periodic synchronization pulses.

[0011] In one embodiment, in the method of digital communication, the aligning further comprises setting a phase of the clock signal based on a trailing edge of the periodic synchronization pulses.

[0012] In one embodiment, in the method of digital communication, the method further comprises: using the clock signal to capture independently acquired measurements from which the digital data is derived.

[0013] In one embodiment, in the method of digital communication, the captured measurements comprise timestamp information. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 Block diagram of an exemplary controller area network.

[0015] Figure 2 Circuit schematic of an exemplary digital communication bus.

[0016] Figure 3 Timing diagram showing various exemplary signal waveforms in the system.

[0017] Figure 4 Graph of clock synchronization phase.

[0018] Figure 5 Flowchart of an exemplary method of digital communication. DETAILED DESCRIPTION

[0019] It is to be understood that the following description and figures are provided for explanatory purposes only and are not limiting of the disclosure. In other words, they are provided to give a basis for one of ordinary skill in the art to identify and understand all modifications, equivalents, and alternatives that fall within the scope of the claims.

[0020] Figure 1An exemplary controller area network (CAN) such as can exist in an automotive environment is shown. An electronic control unit (ECU) 102 is coupled via point-to-point connections forming a star topology to various sensors 103 including a LIDAR (light detection and ranging) unit 104 and a camera 105. Other bus topologies such as tree, ring, and daisy chain can also be suitable. To provide automated driver assistance, the ECU 102 can be further connected to a set of actuators such as a turn signal actuator 106, a steering actuator 108, a brake actuator 110, and a throttle actuator 112. The ECU 102 can be further coupled to an interactive interface 114 to accept user input and provide displays of various measurements and system status. Using the interface, sensors, and actuators, the ECU 102 can provide automated parking, assist parking, lane change assist, obstacle and blind spot detection, and other desired features.

[0021] Figure 2 A schematic diagram of an exemplary data bus having a bus controller 202 (such as the ECU 102) located on a first printed circuit board 204 coupled to a sensor 206 located on a second printed circuit board 208 is shown. The first PCB 204 includes a low dropout (LDO) regulator 210 and a ground connection to supply power to the second PCB 208 via respective conductors V+, GND. A pair of differential signal conductors A, B carry downlink signals from the bus controller 202 to the sensor 206 and uplink signals from the sensor to the bus controller.

[0022] The PCB can include termination circuits 212, 214 to provide impedance matching and / or electromagnetic compatibility by attenuating higher frequencies. The termination circuits are shown here as two equal impedances Zl connected in series between conductor A and conductor B, with an optional impedance Z2 coupled between the intermediate node and ground. The impedances Zl, Z2 can be selected to provide a desired low pass cutoff frequency.

[0023] The bus controller 202 shown includes a transmitter 216 for alternately sending downlink signals TX M and a receiver 218 for receiving uplink signals RX Mtransceiver 220. A universal asynchronous receiver / transmitter (UART) module 222 makes the downlink signal to carry commands and data from a microcontroller unit (MCU) 224, and decodes the uplink signal to provide responses and measurements from the sensor 206 to the MCU 224. Optionally (e.g., for RS485 type transceivers), the UART module 222 provides a T / R signal to the transceiver 220 to switch between transmit and receive modes. CAN compliant transceivers do not require a signal to transition between transmit and receive modes. An oscillator 226 provides a clock signal to the UART module 222. The operations of the UART are performed in accordance with the clock signal, and thus the clock signal determines the timing of symbol transitions in the downlink signal.

[0024] The illustrated sensor 206 similarly includes a transceiver 230 that alternately receives a downlink signal RX S and transmits an uplink signal TX S operating optionally in response to a T / R signal from a UART module 232. A controller 234 receives downlink commands and parameters that configure the operation of the sensor, and provides measurements from a transducer circuit 235 to the UART 232 for conversion into an upload message. An oscillator 236 provides a clock signal for use by the UART 232. As described further below, the clock signal generated by the oscillator 236 can be aligned with the periodic synchronization pulses from the bus controller 202, enabling the UART 232 to generate an uplink message with symbols that are synchronized to the clock signal generated by the oscillator 226.

[0025] Figure 3 Exemplary timing relationships between the various signal waveforms that can be present on the digital communication bus are illustrated. Once the configuration of the sensor is complete, the bus controller transmits periodic synchronization pulses as illustrated in waveform TX M The illustrated pulses are three bit intervals wide, but this is not a requirement. Waveform RX S illustrates the synchronization pulses with a slight delay due to propagation time through the conductors and interface electronics.

[0026] The sensor responds with an uplink waveform TX S which is shown here as a template for three UART standard bytes, each with a single start bit before the least significant bit and a stop bit after the most significant bit. Additional stop bits can be preferred in some systems, and skipped stop bits can be preferred in other systems. Other message formats will also be suitable, e.g., a larger or smaller number of bytes, different bit ordering and / or different word lengths between start and stop bits. Waveform RX MThe delayed uplink waveform is shown to represent the propagation time from the sensor to the bus controller.

[0027] Figure 3 The last two curves show the differential voltage between the signal conductors A, B on the master side and the sensor side, respectively. (The effect of the propagation delay is exaggerated for illustrative purposes.) The sensor can use the interval between the leading edges of the sync pulses as a synchronization period measurement (PM) from which to derive the bit period (or more generally, "symbol period"), and can use the trailing edge of the sync pulse as a zero-phase alignment for the transmit symbol clock.

[0028] As Figure 4 shown, the synchronization and alignment process can be performed across multiple sync pulse periods. An initial calibration period begins upon power-up or when the sensor is reset. Upon detecting a sync pulse, the sensor begins taking period measurements between the leading edges of the pulses. In one contemplated implementation, the sensor uses a local voltage-controlled oscillator coupled to a counter or "frequency divider." The control voltage is set to a default mid-range value, and the most significant bit of the adjustment value is set. If the next sync pulse arrives before the counter expires, the control voltage is increased by the adjustment value to increase the local oscillator frequency. Conversely, if the counter expires before the next sync pulse arrives, the control voltage is decreased by the adjustment value to the offset value to decrease the local oscillator frequency. The adjustment value is then halved so that only its second most significant bit is asserted. This process is repeated until only the least significant bit of the adjustment value is asserted.

[0029] Once the minimum adjustment value is reached and applied, the sensor can transition from calibration mode to tracking mode. During tracking mode, the sensor sends measurement data in response to each sync pulse, but monitors the period between sync pulses and adds or subtracts the minimum adjustment value from the control voltage after each period measurement. In some implementations, the sensor can detect when the adjustment is alternating regularly on a symbol and can apply an error filter or can otherwise increase the number of sync pulses for each adaptation of the control voltage.

[0030] Figure 5A flowchart of an exemplary data communication method that can be implemented by a sensor device. In block 501, the sensor monitors a conductor for a pulse edge in a differential signal. In block 502, the sensor tests whether the edge is a leading edge of a synchronization pulse, and if not, determines whether the calibration phase is complete in block 504. If calibration is in progress, control returns to block 501. Otherwise, in block 506, the sensor uses the edge to initiate transmission of a data frame to the bus controller. It is desirable to acquire the measurement data being transmitted independent of the synchronization signal, and thus a particular implementation requiring increased precision can transmit a measurement timestamp with the measurement data. After the data frame is complete, control returns to block 501.

[0031] If in block 502, the sensor determines that the edge is a leading edge, then in block 508, the sensor determines whether the local oscillator frequency is too high or too low. In block 510, the sensor determines whether the calibration phase is in progress, and if so, in block 512, the oscillator frequency is adjusted using a timing error with a coarse adjustment value. As previously described, the coarse adjustment value decreases with each cycle until the calibration phase is complete.

[0032] If in block 510, it is determined that the calibration phase is complete, then in block 514, the sensor checks whether the initial tracking phase is complete. During the initial tracking phase, the sensor only performs least significant bit (LSB) adjustment of the oscillator control voltage to provide fine adjustment of the oscillator period in block 516. Once the local oscillator frequency / period converges, the sensor can use timing error measurements from multiple synchronization pulse cycles to provide adaptive optimization in block 518.

[0033] While the operations shown and described in Figure 5 are considered to occur in sequence, in practice, the method can be performed by multiple integrated circuit components operating simultaneously. This sequential discussion is not intended to be limiting.

[0034] The clock synchronization implemented between the sensor and the bus controller is expected to allow much higher data transmission rates, including rates higher than about 8 Mbps on a bus otherwise compliant with the CAN-FD automotive bus standard. The disclosed synchronization interface clock configuration enables the sensor to continuously supply measurement information to the controller using a minimal but robust signaling protocol without limiting the manner in which the sensor acquires the measurement information, as compared to other bus types such as buses in which the bus controller employs a query and response protocol to selectively retrieve data from multiple addressable sensor devices.

[0035] In general terms, various embodiments have been disclosed. An exemplary sensor includes a clock signal generator, a bus interface coupled to a differential signal conductor to detect periodic synchronization pulses from a bus controller, and a controller to align a clock signal from the clock signal generator with the periodic synchronization pulses. The bus interface sends digital data to the bus controller between the periodic synchronization pulses, using the clock signal to control symbol transitions.

[0036] An exemplary controller area network includes a bus controller coupled to a pair of differential signal conductors to transmit periodic synchronization pulses, a sensor coupled to the pair of differential signal conductors to receive the periodic synchronization pulses, the sensor having a controller to align a clock signal with the periodic synchronization pulses, and a bus interface to send digital data to the bus controller between the periodic synchronization pulses, using the clock signal to control symbol transitions.

[0037] An exemplary digital communication method includes generating a local clock signal, aligning the local clock signal with periodic synchronization pulses from a bus controller, and sending digital data to the bus controller between the periodic synchronization pulses, using the clock signal to control symbol transitions.

[0038] Each of the foregoing embodiments can be employed individually or in combination, and they can further employ one or more of the following optional features in any suitable combination. 1. As part of the alignment, the controller adjusts a period of the clock signal to match 1 / N of a period of the synchronization pulses, N being an integer. 2. The controller uses a leading edge of the synchronization pulses to determine the period of the clock signal. 3. The controller uses a trailing edge of the synchronization pulses to set a phase of the clock signal. 4. As part of the alignment, the controller performs a coarse calibration phase before the bus interface begins sending digital data. 5. As part of the alignment, the controller performs an adaptive tracking phase after the bus interface begins sending digital data. 6. The controller uses the clock signal to capture measurement results from transducer electronics that collect the measurement results independently of the clock signal and derive digital data therefrom. 7. The controller uses the clock signal to capture independently acquired measurement results from which the digital data is derived from the measurement results. 8. The captured measurement results include timestamp information.

Claims

1. A sensor, comprising: a clock signal generator; a bus interface coupled to a differential signal conductor and configured to detect periodic synchronization pulses from a bus controller, each of the periodic synchronization pulses initiating an interval for sending a data frame to the bus controller without further data transmission from the bus controller; and a controller configured to align a clock signal from the clock signal generator with the periodic synchronization pulses, the bus interface configured to send data frames to the bus controller between the periodic synchronization pulses and to use the clock signal to control symbol transitions. As part of the alignment, the controller is configured to adjust a period of the clock signal to match 1 / N of a period of the synchronization pulses, N being an integer.

2. The sensor of claim 1, wherein, The controller is configured to determine the period of the clock signal using only a leading edge of the synchronization pulses.

3. The sensor of claim 1, wherein, The controller is configured to set a phase of the clock signal using only a trailing edge of the synchronization pulses.

4. The sensor of claim 3, wherein, As part of the alignment, the controller is configured to perform a coarse calibration phase before the bus interface begins sending data frames.

5. The sensor of claim 1, wherein, As part of the alignment, the controller is configured to perform an adaptive tracking phase after the bus interface begins sending data frames.

6. The sensor of claim 5, wherein, 7. The sensor of claim 1, further comprising transducer electronics configured to collect measurement results independent of the clock signal, the controller configured to use the clock signal to capture the measurement results and derive the data frames from the measurement results.

8. A controller area network, comprising: a bus controller coupled to a pair of differential signal conductors and configured to send periodic synchronization pulses, each of the periodic synchronization pulses initiating an interval for sending a data frame to the bus controller without further data transmission from the bus controller; a sensor coupled to the pair of differential signal conductors and configured to receive the periodic synchronization pulses, the sensor comprising: a controller configured to align a clock signal with the periodic synchronization pulses, and a bus interface configured to send data frames to the bus controller between the periodic synchronization pulses and to use the clock signal to control symbol transitions. As part of the alignment, the controller is configured to adjust a period of the clock signal to match 1 / N of a period of the synchronization pulses, N being an integer.

9. The controller area network of claim 8, wherein, The controller is configured to determine the period of the clock signal using only a leading edge of the synchronization pulses.

10. The controller area network of claim 8, wherein, The controller is configured to set a phase of the clock signal using only a trailing edge of the synchronization pulses.

11. The controller area network of claim 10, wherein, As part of the alignment, the controller is configured to perform a coarse calibration phase before the bus interface begins sending data frames.

12. The controller area network of claim 8, wherein, As part of the alignment, the controller is configured to perform an adaptive tracking phase after the bus interface begins sending data frames.

13. The controller area network of claim 12, wherein, ​ 14. The controller area network of claim 8, wherein, The sensor further comprises transducer electronics configured to collect measurement results independent of the clock signal, the controller being configured to use the clock signal to capture the measurement results and derive the data frame from the measurement results.

15. A method of digital communication, wherein, The digital communication method comprises: generating a local clock signal; aligning the local clock signal with periodic synchronization pulses from a bus controller, each of the periodic synchronization pulses initiating an interval for sending a data frame to the bus controller without further data transmission from the bus controller; and sending data frames to the bus controller between the periodic synchronization pulses and using the clock signal to control symbol transitions.

16. The method of claim 15, wherein, The aligning comprises deriving a period of the clock signal from a leading edge of only the periodic synchronization pulses.

17. The method of claim 16, wherein, The aligning further comprises setting a phase of the clock signal based on a trailing edge of only the periodic synchronization pulses.

18. The method of claim 15, further comprising: using the clock signal to capture independently acquired measurement results, wherein the data frame is derived from the measurement results.

19. The method of claim 18, wherein, The captured measurement results comprise timestamp information.

20. The method of claim 15, wherein, The aligning comprises performing a coarse calibration phase before sending data frames and performing an adaptive tracking phase after the bus interface starts sending data frames.

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