Vehicle communications network transceiver, bus driver therefor

A transceiver in nodes of a multiple node vehicle communications network having a communications bus prescribed for use in an automotive industrial standard data link, interconnecting the nodes, each node providing an input device for converting a chosen measurand into digital pulses appearing at varying rates in response to changes of the measurand into symmetrical, variable pulse width modulated (VPWM) trapezoidal shaped waveform signals, the waveform signals containing symbol information expressing the magnitudes of the measurand, each node containing a regulated power source connected to a vehicle battery to provide regulated logic voltages referenced with respect to a signal ground return;

• each node also containing a microcontroller (MCU) connected between the input device, power source and a symbol encoder decoder (SED), for receiving digital pulses from the input device representing magnitudes of the measurands, formatting the received digital pulses into digital messages, polling input and output ports connected to the SED, and initiating transmission over the bus via the SED, the SED being interconnected between the MCU and the transceiver for translating the digital messages from the MCU into said VPWM square-wave, line codings sent to other transceivers connected to the bus and for converting square wave digital signals received from other transceivers into digital messages used by the MCU for updating or controlling other peripherals associated with the network, said transceiver comprising:
• (a) an integrator with an input for receiving the VPWM square-wave pulses from SED having pulse widths that define symbol information with respect to time and logic levels, and producing at an output terminal trapezoid type waveform signals with pulses 180 degrees out of phase with the square wave pulses and referenced with respect to a fixed voltage level;
• (b) a waveshaper having an input for receiving the trapezoid waveform signals from the integrator and reshaping both corners at the extremities of each edge of the pulses over a chosen duration and then producing at an output terminal other trapezoid waveform signals in phase with the input waveform signals having the same pulse width as the input trapezoid signals at trip point voltages so as to retain the symbol information contained in the original square-wave signals, the reshaped trapezoid signals being referenced with respect to another fixed voltage level different from signal ground;
• (c) a voltage-to-current converter having an input for receiving the reshaped trapezoid waveform signals from the waveshaper, and providing at an output a replica of the reshaped trapezoid waveform signals used as control current source signals, said control current source signals being routed to a current sensor circuit within the voltage-to-current converter to provide pulse voltage potentials with respect to signal ground return of magnitudes proportional to the voltage across the current sensor;
• (d) a ground translation circuit including a current mirror circuit having an input connected to the current sensor circuit of the voltage-to-current converter so that the current in an input circuit corresponds with the current flowing through the current sensor of the voltage-to-current converter, the ground translation circuit having an output circuit connected to carry a reflected current of the same magnitude and direction as the current in the current mirror input circuit but the output current is referenced with respect to an independent bus ground return, the ground translation circuit also having an output reference voltage circuit used to establish a reference voltage signal referenced with respect to the independent ground return but which establishes voltage levels in response to varying current signals from the output circuit of the current mirror;
• d) a bus driver connected between the battery of the vehicle and the independent bus ground return, the bus driver comprising another current mirror circuit having an input circuit used to receive pulse signals from the reference voltage circuit of the ground translation circuit and for using the received pulse signals to program the current in an output circuit of the another current mirror, the programmed current causing a reflected current of an enhanced magnitude and of the same direction as the reference voltage and current to flow out of the output circuit of the another current mirror circuit, the bus driver having an output circuit connected between the output of the another current mirror and the bus for sourcing current onto the bus when the bus voltage levels permit transmitting and for cutting off the source current from the current mirror when the bus voltage levels inhibit transmitting;
• and
• (e) a receiver circuit interconnected between the bus and SED for receiving reshaped trapezoid waveform signals from the bus and extracting symbol information contained in the waveform signals and converting the extracted symbol information into digital pulse signals with pulse durations equivalent to the symbol information.